Fix: call_rcu: teardown default call_rcu worker on application exit

Teardown the default call_rcu worker thread if there are no queued
callbacks on process exit. This prevents leaking memory.

Here is how an application can ensure graceful teardown of this
worker thread:

- An application queuing call_rcu callbacks should invoke
  rcu_barrier() before it exits.
- When chaining call_rcu callbacks, the number of calls to
  rcu_barrier() on application exit must match at least the maximum
  number of chained callbacks.
- If an application chains callbacks endlessly, it would have to be
  modified to stop chaining callbacks when it detects an application
  exit (e.g. with a flag), and wait for quiescence with rcu_barrier()
  after setting that flag.
- The statements above apply to a library which queues call_rcu
  callbacks, only it needs to invoke rcu_barrier in its library
  destructor.

Fixes: #1317
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I40556bc872d3df58a22fb88a0dbb528ce5c9b4af

Fix: join worker thread in call_rcu_data_free

When freeing the call rcu descriptor, join its associated thread as well
to ensure complete teardown.

Fixes: #1317
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ic522e0466f56deca8bde519e082f3d7f99ec2e7f

Fix: auto-resize hash table destroy deadlock

Fix a deadlock for auto-resize hash tables when cds_lfht_destroy
is called with RCU read-side lock held.

Example stack track of a hang:

  Thread 2 (Thread 0x7f21ba876700 (LWP 26114)):
  #0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  #1  0x00007f21beba7aa0 in futex (val3=0, uaddr2=0x0, timeout=0x0, val=-1, op=0, uaddr=0x7f21bedac308 <urcu_memb_gp+8>) at ../include/urcu/futex.h:81
  #2  futex_noasync (timeout=0x0, uaddr2=0x0, val3=0, val=-1, op=0, uaddr=0x7f21bedac308 <urcu_memb_gp+8>) at ../include/urcu/futex.h:90
  #3  wait_gp () at urcu.c:265
  #4  wait_for_readers (input_readers=input_readers@entry=0x7f21ba8751b0, cur_snap_readers=cur_snap_readers@entry=0x0,
      qsreaders=qsreaders@entry=0x7f21ba8751c0) at urcu.c:357
  #5  0x00007f21beba8339 in urcu_memb_synchronize_rcu () at urcu.c:498
  #6  0x00007f21be99f93f in fini_table (last_order=<optimized out>, first_order=13, ht=0x5651cec75400) at rculfhash.c:1489
  #7  _do_cds_lfht_shrink (new_size=<optimized out>, old_size=<optimized out>, ht=0x5651cec75400) at rculfhash.c:2001
  #8  _do_cds_lfht_resize (ht=ht@entry=0x5651cec75400) at rculfhash.c:2023
  #9  0x00007f21be99fa26 in do_resize_cb (work=0x5651e20621a0) at rculfhash.c:2063
  #10 0x00007f21be99dbfd in workqueue_thread (arg=0x5651cec74a00) at workqueue.c:234
  #11 0x00007f21bd7c06db in start_thread (arg=0x7f21ba876700) at pthread_create.c:463
  #12 0x00007f21bd4e961f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

  Thread 1 (Thread 0x7f21bf285300 (LWP 26098)):
  #0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  #1  0x00007f21be99d8b7 in futex (val3=0, uaddr2=0x0, timeout=0x0, val=-1, op=0, uaddr=0x5651d8b38584) at ../include/urcu/futex.h:81
  #2  futex_async (timeout=0x0, uaddr2=0x0, val3=0, val=-1, op=0, uaddr=0x5651d8b38584) at ../include/urcu/futex.h:113
  #3  futex_wait (futex=futex@entry=0x5651d8b38584) at workqueue.c:135
  #4  0x00007f21be99e2c8 in urcu_workqueue_wait_completion (completion=completion@entry=0x5651d8b38580) at workqueue.c:423
  #5  0x00007f21be99e3f9 in urcu_workqueue_flush_queued_work (workqueue=0x5651cec74a00) at workqueue.c:452
  #6  0x00007f21be9a0c83 in cds_lfht_destroy (ht=0x5651d8b2fcf0, attr=attr@entry=0x0) at rculfhash.c:1906

This deadlock is easy to reproduce when rapidly adding a large number of
entries in the cds_lfht, removing them, and calling cds_lfht_destroy().

The deadlock will occur if the call to cds_lfht_destroy() takes place
while a resize of the hash table is ongoing.

Fix this by moving the teardown of the lfht worker thread to libcds
library destructor, so it does not have to wait on synchronize_rcu from
a resize callback from within a read-side critical section. As a
consequence, the atfork callbacks are left registered within each urcu
flavor for which a resizeable hash table is created until the end of the
executable lifetime.

The other part of the fix is to move the hash table destruction to the
worker thread for auto-resize hash tables. This prevents having to wait
for resize callbacks from RCU read-side critical section. This is
guaranteed by the fact that the worker thread serializes previously
queued resize callbacks before the destroy callback.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: If8b1c3c8063dc7b9846dc5c3fc452efd917eab4d

Fix building on MSYS2

Update cygwin libtool config in `configure.ac` to match MSYS2 build
environments as well. MSYS2 is also a Windows build environment that
produces DLLs.

Signed-off-by: Christopher Ng <facboy@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I48ca648123fd40b8003c72c0447c70a8b4bde6d6

Fix: Remove include urcu/assert.h

Bad backport.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Iee78c68ce593f09f74ef969ccaa34eb8182ed150

rculfhash: Include rculfhash-internal.h from local directory

Use double quotes rather than angle brackets to include this local
header file. This fixes build scenarios where the liburcu build is used
from cmake.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Iad6c9765ecc409c8df3a659975c97a3c068d5c0a

Fix: Always check pthread_create for failures

pthread_create may fail with EAGAIN (which is no fault of the
programmer), so don't allow the check to be compiled out.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ia2695ea6953b589ac8ab8b444fb668daee06a614

Version 0.13.2

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ibe3b1cbaa174107d0aabce1fa61a38ead354e1ed

Revert "Fix: remove type constness in URCU_FORCE_CAST's C++ version"

This reverts commit 342602dc6dc67d92a6f5ddcbe6ae407c87cb4c6b.

This adds a dependency on c++11, which is not present in the stable-0.13
branch README.md file.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I8c586b03cb94fdb4f28ca7de254b1be4e2c48acd

Fix: futex.h: include headers outside extern C

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ia8aac42e74d1d401cd893a30afb9cbde29a993d5

Fix: add missing unused attribute to _rcu_dereference

Reproduced with gcc-8, gcc-10, gcc-11 in O2:

14:39:19 In file included from ../../include/urcu/pointer.h:39,
14:39:19                  from ../../include/urcu-pointer.h:1,
14:39:19                  from ../../include/urcu/rcuhlist.h:30,
14:39:19                  from ../../include/urcu/cds.h:28,
14:39:19                  from test_build.c:30:
14:39:19 test_build.c: In function ‘test_build_rcu_dereference’:
14:39:19 ../../include/urcu/static/pointer.h:102:55: warning: variable ‘_________p0’ set but not used [-Wunused-but-set-variable]
14:39:19   102 |                                         __typeof__(p) _________p0 = { 0 };              \
14:39:19       |                                                       ^~~~~~~~~~~
14:39:19 ../../include/urcu/pointer.h:47:33: note: in expansion of macro ‘_rcu_dereference’
14:39:19    47 | #define rcu_dereference         _rcu_dereference
14:39:19       |                                 ^~~~~~~~~~~~~~~~
14:39:19 test_build.c:133:9: note: in expansion of macro ‘rcu_dereference’
14:39:19   133 |         rcu_dereference(opaque_const);
14:39:19       |         ^~~~~~~~~~~~~~~
14:39:19 mv -f .deps/test_urcu_multiflavor_single_unit_dynlink_cxx-test_urcu_multiflavor_single_unit_cxx.Tpo .deps/test_urcu_multiflavor_single_unit_dynlink_cxx-test_urcu_multiflavor_single_unit_cxx.Po
14:39:19 ../../include/urcu/static/pointer.h:102:55: warning: variable ‘_________p0’ set but not used [-Wunused-but-set-variable]
14:39:19   102 |                                         __typeof__(p) _________p0 = { 0 };              \
14:39:19       |                                                       ^~~~~~~~~~~
14:39:19 ../../include/urcu/pointer.h:47:33: note: in expansion of macro ‘_rcu_dereference’
14:39:19    47 | #define rcu_dereference         _rcu_dereference
14:39:19       |                                 ^~~~~~~~~~~~~~~~
14:39:19 test_build.c:135:9: note: in expansion of macro ‘rcu_dereference’
14:39:19   135 |         rcu_dereference(clear_const);
14:39:19       |         ^~~~~~~~~~~~~~~

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: If3a78c2ec1c3ae0cab1ea5f9d40ede4e30f9bc81

Fix: change method used by _rcu_dereference to strip type constness

Commit 1e41ec3b07e4 ("Make temporary variable in _rcu_dereference
non-const") used the trick to add 0 to the pointer passed as a parameter
to the macro to get rid of its constness, should it be const (with the
end goal of avoiding compiler warnings).  This is problematic (as shown
in [1]) if it is a pointer to an opaque type though, as the compiler
cannot perform pointer arithmetic on such a pointer (even though it
wouldn't really need to here, as we add 0).

Change it to use another trick to strip away the constness, that
shouldn't hit this problem.  It was found in the same stackoverflow post
as the original trick [2].  It consists of using a statement expression
like so:

    __typeof__(({ const int foo; foo; }))

The statement expression yields a value of type `int`.  Statement
expressions are extensions to the C language, but we already use them
here.

[1] https://lists.lttng.org/pipermail/lttng-dev/2022-August/030247.html
[2] https://stackoverflow.com/a/54016713

Change-Id: Ic73590ef4beaa1832161aa05a6df37e467f85116
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Fix: remove type constness in URCU_FORCE_CAST's C++ version

The test added by the following patch wouldn't compile, when built
without _LGPL_SOURCE:

      CXX      test_build_dynlink_cxx-test_build_cxx.o
    In file included from ../../include/urcu/arch.h:25,
                     from /home/simark/src/urcu/tests/unit/test_build.c:28,
                     from /home/simark/src/urcu/tests/unit/test_build_cxx.cpp:3:
    /home/simark/src/urcu/tests/unit/test_build.c: In function ‘void test_build_rcu_dereference()’:
    /home/simark/src/urcu/include/urcu/compiler.h:85:42: error: type qualifiers ignored on cast result type [-Werror=ignored-qualifiers]
       85 | #define URCU_FORCE_CAST(type, arg)      (reinterpret_cast<type>(arg))
          |                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~
    /home/simark/src/urcu/include/urcu/pointer.h:71:49: note: in expansion of macro ‘URCU_FORCE_CAST’
       71 |                 __typeof__(p) _________p1 =     URCU_FORCE_CAST(__typeof__(p), \
          |                                                 ^~~~~~~~~~~~~~~
    /home/simark/src/urcu/tests/unit/test_build.c:133:9: note: in expansion of macro ‘rcu_dereference’
      133 |         rcu_dereference(opaque_const);
          |         ^~~~~~~~~~~~~~~

The compiler complains that we do a cast to a const type, equivalent to:

  reinterpret_cast<const int>(arg)

... and that the const is meaningless in this context.

Use std::remove_cv to strip away any const or volatile qualifiers from
the type (using a volatile type would result in the same warning).

Change-Id: I94e79fcccfc2108021752f65977e1548084c646a
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Move extern "C" down in include/urcu/urcu-bp.h

A following patch adds a <type_traits> include in
urcu/compiler.h.  However, compiler.h gets included by urcu/pointer.h,
which gets included by urcu/urcu-bp.h inside an extern "C" scope.
Including the C++ header file <type_traits> inside an extern "C" scope
doesn't work:

    In file included from /home/simark/src/urcu/include/urcu/compiler.h:25,
                     from /home/simark/src/urcu/include/urcu/pointer.h:29,
                     from /home/simark/src/urcu/include/urcu/urcu-bp.h:58,
                     from /home/simark/src/urcu/include/urcu-bp.h:2,
                     from /home/simark/src/urcu/tests/unit/test_urcu_multiflavor-bp.c:28,
                     from /home/simark/src/urcu/tests/unit/test_urcu_multiflavor-bp_cxx.cpp:3:
    /usr/include/c++/12.1.1/type_traits:44:3: error: template with C linkage
       44 |   template<typename _Tp>
          |   ^~~~~~~~
    /home/simark/src/urcu/include/urcu/urcu-bp.h:41:1: note: ‘extern "C"’ linkage started here
       41 | extern "C" {
          | ^~~~~~~~~~

Move the extern "C" in urcu-bp.h down, so that the includes are not
inside it.  Each header file is responsible to use extern "C" where
relevant, and we should avoid including files inside such a scope.

Change-Id: I42bdfa6ab445e8c40f5bcac1c1ae0786d443626c
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: ifdef linux specific cpu count compat

Expand the '#ifdef __linux__' block in src/compat-cpu.h to all static
inline functions related to sysfs since they are only useful on Linux
and fail to build on some non-Linux platforms. This issue was reported
on QNX.

Thanks to Elad Lahav <e2lahav@gmail.com> for reporting this issue.

Change-Id: I17c88a9a2fb5b9be6cf5325234a18ff40788cd09
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Set git-review branch to stable-0.13

Change-Id: Id2a103eb9ff3ea0e81d88dad42d2eac9d365156c
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: sysconf(_SC_NPROCESSORS_CONF) can be less than max cpu id

We rely on sysconf(_SC_NPROCESSORS_CONF) to get the maximum possible
number of CPUs that can be attached to the system for the lifetime of an
application.

As such we expect that the highest possible CPU id would be one less
than the number returned by sysconf(_SC_NPROCESSORS_CONF) which is
unfortunatly not always the case and can vary across libc
implementations and versions.

Glibc up to 2.35 will count the number of "cpuX" directories in
"/sys/devices/system/cpu" which doesn't include CPUS that were
hot-unplugged.

This information is however provided by the Linux kernel in
"/sys/devices/system/cpu/possible" in the form of a mask listing all the
CPUs that could possibly be hot-plugged in the system.

This patch replaces sysconf(_SC_NPROCESSORS_CONF) with an internal
function that first tries parsing the possible CPU mask to extract the
highest possible value and if this fails fallback to the previous
behavior.

Change-Id: I68dfed42ebbab02728a02eeefd4a395a22bb1bea
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Fix: revise obsolete command in README.md

The obsolete command `make bench` was replaced by `make short_bench` and
`make long_bench` in 2015.  However, this command wasn't revised in
README, so I follow the previous commit and rewrite it.

Signed-off-by: Shao-Tse Hung <ccs100203@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I92fa6cc3937b0a65b0a005ce6bb1fe3d2b3250ab

Fix: workqueue: remove unused variable "ret"

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I57eddb10fd90b680ee71966e6eb6a327d8c51063

Fix: urcu-qsbr: futex wait: handle spurious futex wakeups

Observed issue
==============

The urcu-qsbr wait_gp() implements a futex wait/wakeup scheme identical to
the workqueue code, which has an issue with spurious wakeups.

A spurious wakeup on wait_gp can cause wait_gp to return with a
urcu_qsbr_gp.futex state of -1, which is unexpected. It would cause the
following loops in wait_for_readers() to decrement the
urcu_qsbr_gp.futex to values below -1, thus actively using CPU as values
will be decremented to very low negative values until it reaches 0
through underflow, or until the input_readers list is found to be empty.
The state is restored to 0 when the input_readers list is found to be
empty, which restores the futex state to a correct state for the
following calls to wait_for_readers().

This issue will cause spurious unexpected high CPU use, but will not
lead to data corruption.

Cause
=====

From futex(5):

       FUTEX_WAIT
              Returns 0 if the caller was woken up.  Note that a  wake-up  can
              also  be caused by common futex usage patterns in unrelated code
              that happened to have previously used the  futex  word's  memory
              location  (e.g., typical futex-based implementations of Pthreads
              mutexes can cause this under some conditions).  Therefore, call‐
              ers should always conservatively assume that a return value of 0
              can mean a spurious wake-up, and  use  the  futex  word's  value
              (i.e.,  the user-space synchronization scheme) to decide whether
              to continue to block or not.

Solution
========

We therefore need to validate whether the value differs from -1 in
user-space after the call to FUTEX_WAIT returns 0.

Known drawbacks
===============

None.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I87f7cd3b02820cefe850c3bdb8da27fb2f9be9b2

Fix: urcu: futex wait: handle spurious futex wakeups

Observed issue
==============

The urcu wait_gp() implements a futex wait/wakeup scheme identical to
the workqueue code, which has an issue with spurious wakeups.

A spurious wakeup on wait_gp can cause wait_gp to return with a
rcu_gp.futex state of -1, which is unexpected. It would cause the
following loops in wait_for_readers() to decrement the
rcu_gp.futex to values below -1, thus actively using CPU as values
will be decremented to very low negative values until it reaches 0
through underflow, or until the input_readers list is found to be empty.
The state is restored to 0 when the input_readers list is found to be
empty, which restores the futex state to a correct state for the
following calls to wait_for_readers().

This issue will cause spurious unexpected high CPU use, but will not
lead to data corruption.

Cause
=====

From futex(5):

       FUTEX_WAIT
              Returns 0 if the caller was woken up.  Note that a  wake-up  can
              also  be caused by common futex usage patterns in unrelated code
              that happened to have previously used the  futex  word's  memory
              location  (e.g., typical futex-based implementations of Pthreads
              mutexes can cause this under some conditions).  Therefore, call‐
              ers should always conservatively assume that a return value of 0
              can mean a spurious wake-up, and  use  the  futex  word's  value
              (i.e.,  the user-space synchronization scheme) to decide whether
              to continue to block or not.

Solution
========

We therefore need to validate whether the value differs from -1 in
user-space after the call to FUTEX_WAIT returns 0.

Known drawbacks
===============

None.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I83942e24c32e77395ff25b466f1b1640422b9eb5

Fix: urcu-wait: futex wait: handle spurious futex wakeups

Observed issue
==============

The urcu-wait urcu_adaptative_busy_wait() implements a futex wait/wakeup
scheme similar to the workqueue code, which has an issue with spurious
wakeups.

A spurious wakeup on urcu_adaptative_busy_wait can cause
urcu_adaptative_busy_wait to reach label skip_futex_wait with a
wait->state state of URCU_WAIT_WAITING, which is unexpected. It would
cause busy-waiting on URCU_WAIT_TEARDOWN state to start early. The
wait-teardown stage is done with URCU_WAIT_ATTEMPTS active attempts,
following by attempts spaced by 10ms sleeps. I do not expect that these
spurious wakeups will cause user-observable effects other than being
slightly less efficient that it should be.

urcu-wait is used by all urcu flavor's synchronize_rcu() to implement
the grace period batching scheme.

This issue will cause spurious unexpected high CPU use, but will not
lead to data corruption.

Cause
=====

From futex(5):

       FUTEX_WAIT
              Returns 0 if the caller was woken up.  Note that a  wake-up  can
              also  be caused by common futex usage patterns in unrelated code
              that happened to have previously used the  futex  word's  memory
              location  (e.g., typical futex-based implementations of Pthreads
              mutexes can cause this under some conditions).  Therefore, call‐
              ers should always conservatively assume that a return value of 0
              can mean a spurious wake-up, and  use  the  futex  word's  value
              (i.e.,  the user-space synchronization scheme) to decide whether
              to continue to block or not.

Solution
========

We therefore need to validate whether the value differs from
URCU_WAIT_WAITING in user-space after the call to FUTEX_WAIT returns 0.

Known drawbacks
===============

None.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I8e9586597f091efc633f3310a68d18b0bd8de1e0

Fix: defer_rcu: futex wait: handle spurious futex wakeups

Observed issue
==============

The urcu-defer wait_defer() implements a futex wait/wakeup scheme identical to
the workqueue code, which has an issue with spurious wakeups.

A spurious wakeup on wait_defer can cause wait_defer to return with a
defer_thread_futex state of -1, which is unexpected. It would cause the
following loops in thr_defer() to decrement the defer_thread_futex to
values below -1, thus actively using CPU as values will be decremented
to very low negative values until it reaches 0 through underflow, or
until callbacks are eventually queued. The state is restored to 0 when
callbacks are found, which restores the futex state to a correct state
for the following calls to wait_defer().

This issue will cause spurious unexpected high CPU use, but will not
lead to data corruption.

Cause
=====

From futex(5):

       FUTEX_WAIT
              Returns 0 if the caller was woken up.  Note that a  wake-up  can
              also  be caused by common futex usage patterns in unrelated code
              that happened to have previously used the  futex  word's  memory
              location  (e.g., typical futex-based implementations of Pthreads
              mutexes can cause this under some conditions).  Therefore, call‐
              ers should always conservatively assume that a return value of 0
              can mean a spurious wake-up, and  use  the  futex  word's  value
              (i.e.,  the user-space synchronization scheme) to decide whether
              to continue to block or not.

Solution
========

We therefore need to validate whether the value differs from -1 in
user-space after the call to FUTEX_WAIT returns 0.

Known drawbacks
===============

None.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Id9c104c0bb77cc306f0b8fbf0b924bdda2aaaf4c

Fix: call_rcu: futex wait: handle spurious futex wakeups

Observed issue
==============

The urcu call_rcu() and rcu_barrier() each implement a futex wait/wakeup
scheme identical to the workqueue code, which has an issue with spurious
wakeups.

* call_rcu

A spurious wakeup on call_rcu_wait can cause call_rcu_wait to return
with a crdp->futex state of -1, which is unexpected. It would cause the
following loops in call_rcu_thread() to decrement the crdp->futex to
values below -1, thus actively using CPU time as values will be
decremented to very low negative values until the futex value underflows
back to 0. The state is *not* restored to 0 when the callback list is
found to be non-empty, so this unexpected state will persist until the
crdp->futex state underflows back to 0, or until the call_rcu_thread is
stopped. What prevents this from having too much user-observable effects
is that the call rcu thread has a 10ms sleep between loops, to favor
batching of callbacks. Therefore, rather than being a purely 100% active
busy-wait, this scenario leads to a busy-wait which is paced by 10ms
sleeps.

Therefore the observed issue will be that the call_rcu_thread will
unexpectedly wake up the CPU each 10ms after this spurious wakeup
happens.

* rcu_barrier

A spurious wakeup on call_rcu_completion_wait can cause
call_rcu_completion_wait to return with a completion->futex state of -1,
which is unexpected. It would cause the following loops in rcu_barrier()
to decrement the completion->futex to values below -1, thus actively
using CPU time as values will be decremented to very low negative values
until either the barrier count reaches 0 or until the futex value
underflows to 0.

Therefore the observed issue will be that rcu_barrier() will
unexpectedly use a lot of CPU time when this spurious wakeup happens.

These issues will cause spurious unexpected high CPU use, but will not
lead to data corruption.

Cause
=====

From futex(5):

       FUTEX_WAIT
              Returns 0 if the caller was woken up.  Note that a  wake-up  can
              also  be caused by common futex usage patterns in unrelated code
              that happened to have previously used the  futex  word's  memory
              location  (e.g., typical futex-based implementations of Pthreads
              mutexes can cause this under some conditions).  Therefore, call‐
              ers should always conservatively assume that a return value of 0
              can mean a spurious wake-up, and  use  the  futex  word's  value
              (i.e.,  the user-space synchronization scheme) to decide whether
              to continue to block or not.

Solution
========

We therefore need to validate whether the value differs from -1 in
user-space after the call to FUTEX_WAIT returns 0.

Known drawbacks
===============

None.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I3e625f1689462f8eb9f1223b5b24b1a754bad324

Fix: workqueue: futex wait: handle spurious futex wakeups

Observed issue
==============

The workqueue thread futex_wait() returns with a workqueue->futex state
of -1, which is unexpected. In this situation, the workqueue thread is
observed to use 99% of CPU as workqueue->futex values are decremented to
very low negative values while the workqueue is empty.

This issue will cause spurious unexpected high CPU use, but will not
lead to data corruption.

Cause
=====

From futex(5):

       FUTEX_WAIT
              Returns 0 if the caller was woken up.  Note that a  wake-up  can
              also  be caused by common futex usage patterns in unrelated code
              that happened to have previously used the  futex  word's  memory
              location  (e.g., typical futex-based implementations of Pthreads
              mutexes can cause this under some conditions).  Therefore, call‐
              ers should always conservatively assume that a return value of 0
              can mean a spurious wake-up, and  use  the  futex  word's  value
              (i.e.,  the user-space synchronization scheme) to decide whether
              to continue to block or not.

Solution
========

We therefore need to validate whether the value differs from -1 in
user-space after the call to FUTEX_WAIT returns 0.

Known drawbacks
===============

None.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Id024e7d3b2dab75d30fc01280fd27e5f2d8af0d1

Fix: Use %lu rather than %ld to print count

In ht_count_del function, the type of count variable is defined as unsigned long,
so use %lu rather than %ld to print it.

Signed-off-by: yaowenbin1 <yaowenbin1@huawei.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ie2701fa0a8170b05532429b34e0f798e6f27139b

Version 0.13.1

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ie5594529fa0fb46526f81f7bf1aa8825397acd69

Fix: changelog: v0.13.0 was released in 2021

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Iab4b54ac1749a40b9a49bede551afdf24d6d3b47

fix: properly detect 'cmpxchg' on x86-32

We wrongly assumed that on x86-32 when '__i386__' is defined but none of
'__i486__', '__i586__' or '__i686__' that the target arch is a literal
i386 cpu without the cmpxchg instructions. However, when building with
'-march=core2' we get '__i386__' but none of the others even if the arch
is newer than an i686.

Change the compat code to use the '__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4'
builtin define to detect an x86-32 system without the cmpxchg
instructions.

Since this builtin define was introduced in GCC 4.3 and Clang 3.3,
building with older compilers on any x86-32 system will enable the
compat layer regardless of the availability of the instructions.

Change-Id: I8329431e55d778405b2ca7007d90c2c6e5cdd426
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: use urcu-tls compat with c++ compiler

  * Initialize all fields of 'struct urcu_tls' to avoid :

    sorry, unimplemented: non-trivial designated initializers not supported

  * Cast void* to proper type pointers to avoid :

    error: invalid conversion from ‘void*’ to ...

Change-Id: I654f924324cda2eaea723f4a0759d706b2a2bf40
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: remove autoconf features default value in help message

The default values of yes|no can be confusing combined with the
--enable / --disable switches of autoconf, remove them from the help
message.

Change-Id: Id9c4036b2fa50e1144a43f68f71a24f0c11434eb
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: add missing pkgconfig file for memb flavour lib

We ship a pkg-config file for each urcu flavour library except the
latest introduced 'memb'.

Change-Id: If222949941d968f63b07616776440931657aa6db
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Make temporary variable in _rcu_dereference non-const

When building the lttng-tools project with Ubuntu's gcc 11, I get the
following error:

      CC       agent.lo
    In file included from /tmp/lttng/include/urcu/arch.h:25,
                     from /tmp/lttng/include/urcu/uatomic.h:23,
                     from /home/simark/src/lttng-tools/src/bin/lttng-sessiond/agent.c:11:
    /home/simark/src/lttng-tools/src/bin/lttng-sessiond/agent.c: In function ‘agent_update’:
    /tmp/lttng/include/urcu/static/pointer.h:96:33: error: argument 2 of ‘__atomic_load’ discards ‘const’ qualifier [-Werror=incompatible-pointer-types]
       96 |                                 __atomic_load(&(p), &_________p1, __ATOMIC_CONSUME);    \
          |                                 ^~~~~~~~~~~~~
    /tmp/lttng/include/urcu/compiler.h:69:70: note: in definition of macro ‘caa_container_of’
       69 |                 const __typeof__(((type *) NULL)->member) * __ptr = (ptr); \
          |                                                                      ^~~
    /tmp/lttng/include/urcu/rculist.h:87:20: note: in expansion of macro ‘cds_list_entry’
       87 |         for (pos = cds_list_entry(rcu_dereference((head)->next), __typeof__(*(pos)), member); \
          |                    ^~~~~~~~~~~~~~
    /tmp/lttng/include/urcu/pointer.h:47:33: note: in expansion of macro ‘_rcu_dereference’
       47 | #define rcu_dereference         _rcu_dereference
          |                                 ^~~~~~~~~~~~~~~~
    /tmp/lttng/include/urcu/rculist.h:87:35: note: in expansion of macro ‘rcu_dereference’
       87 |         for (pos = cds_list_entry(rcu_dereference((head)->next), __typeof__(*(pos)), member); \
          |                                   ^~~~~~~~~~~~~~~
    /home/simark/src/lttng-tools/src/bin/lttng-sessiond/agent.c:1551:9: note: in expansion of macro ‘cds_list_for_each_entry_rcu’
     1551 |         cds_list_for_each_entry_rcu(ctx, &agt->app_ctx_list, list_node) {
          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~

This is because the pointer passed to _rcu_dereference is const (the
pointer itself is const, IIUC, not necessarily the data it points to),
so the temporary _________p1 is also declared as const.  We therefore
can't pass a non-const pointer to it to a function that modifies it.

I applied the trick found here [1] with success to get rid of the
constness of the variable.  With this change, lttng-tools compiles
successfully with gcc 11.

There may be other spots in the headers where this would be needed, but
it is hard to spot them.  I think we would need to write some test file
that pass const pointers to all macros of the API and see if they
compile.

[1] https://stackoverflow.com/a/18067745

Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ib43efa7674ecea99cec1c3fffae86829b44a97e5

Fix: x86 and s390: uatomic __hp() macro C++ support

C++ does not allow defining types in cast. Therefore, define the types
with typedef and use them in the __hp() macro.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I92af62924f78dc6c5f7420a6376731212fbc5a20

Fix: x86 and s390: uatomic __hp() macro clang support

The __hp macro should receive contant size arguments to support clang,
which does not implement VLA support.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ifa3d5b5b7921f54849e0f331bef8f07c059b998f

Fix: x86 and s390 uatomic: __hp() macro warning with gcc 11

The __hp() macro used in the x86 and s390 uatomic code generates the
following warning with gcc-11:

In file included from ../include/urcu/uatomic.h:27,
                 from ../include/urcu/static/wfcqueue.h:35,
                 from ../include/urcu/wfcqueue.h:133,
                 from workqueue.c:39:
workqueue.c: In function ‘workqueue_thread’:
../include/urcu/uatomic/x86.h:155:17: warning: array subscript ‘struct __uatomic_dummy[0]’ is partly outside array bounds of ‘struct cds_wfcq_tail[1]’ [-Warray-bounds]
  155 |                 __asm__ __volatile__(
      |                 ^~~~~~~
workqueue.c:184:38: note: while referencing ‘cbs_tmp_tail’
  184 |                 struct cds_wfcq_tail cbs_tmp_tail;
      |                                      ^~~~~~~~~~~~

The (previously undocumented) reason for this macro is to allow passing the
"void *" parameter as "m" or "+m" operand to the inline assembly. That
motivation was explained in commit 53b8ed6836363 ("s390 uatomic arch fix").

The out of bound access is detected by gcc because struct
__uatomic_dummy's length is quite large: an array of 10 unsigned long,
which is larger than the size pointed to by the void pointer.

So rather than using a fixed-size type, cast to a structure containing
an array of characters of a size matching the @addr input argument.

While we are at it and digging out git archeology, properly document the
__hp() macro for posterity.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I785e30661efe48be1806664a1a14fd3c9fdb0a32

Version 0.13.0

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: If88881cebb1d64b2669da0edc59e483dedc9d6b7

Document known ABI issue in README.md

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ic4bc9273eb63e051eb1da122bee4f99a8eefafd3

Add serialized ABI definition files

This commit contains the serialized ABI definitions for a typical build
of the liburcu librairies. This information is extracted using
libabigail (https://sourceware.org/libabigail/).

The artefacts used to generate these were built with CFLAGS="-O0 -ggdb".

You can compare the serialized ABI with a shared object to check for
breaking changes. For example, here we compare an in-tree built version
of liburcu-memb.so with the serialized ABI of stable-0.13 :

  abidiff \
    extras/abi/0.13/x86_64-pc-linux-gnu/liburcu-memb.so.7.xml \
    src/.libs/liburcu-memb.so

Change-Id: Icb3145cdf9f69490981ce201ec437cc83298f0a7
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

bump SONAME major to 8

In URCU 0.11, we introduced new symbols to clean up the library symbol
namespacing, using the "alias" attribute to keep emitting the old
symbols, expecting to preserve ABI backward compatibility.
Unfortunately, it turns out that even though it works well for function
symbols, it is broken for public global variables due to the way ELF
copy relocation works.

When building a non-PIC executable that uses an extern variable, a .bss
symbol is emitted in the executable. This will take precedence over the
symbol implemented within the library in the Global Symbol Table.
Unfortunately, the alias within the library will not be aware that the
actual GST symbol differs from its alias within the library, and the
addresses for the symbol and its alias will differ at runtime.

Considering that this compatibility issue affects official library
releases, there is little we can do beyond documenting this issue, and
bumping the Userspace RCU major soname for the next (0.13) release.

Change-Id: I0ca8407dcffd871f025814923c6e329ec260133a
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Remove all SONAME(6) ABI aliases

Those aliases become unneeded with the upcoming soname bump.

Change-Id: Id6c368526d9cb04fc92c12b3f4632b4a9443f41d
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

.gitignore: list ignored Makefiles

We carry some Makefiles in the examples, remove the catchall Makefile
from gitignore and replace it by the list of automake generated
Makefiles.

Change-Id: I06bc46d9035cade7ebecf1a51c3d1983c2734097
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

tests: Add a simple compile test for caa_get_cycles

Change-Id: Id2dbaf5f250a5e6e135700dabed5832e75ca7ce9
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: clock_gettime on macOs

Newer version of macOs have an implementation of clock_gettime() that
requires additionnal setup, move the platform specific code first so it
is always used.

Change-Id: I12fcdeff6c0ae59bc1a13f4e2cd7f4ebcedfc253
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Fix: rculist header: use parenthesis around macro parameters

The coding style followed across liburcu is to use parenthesis around
macro parameters when it would otherwise lead to unexpected results due
to priority of operators. Fix rculist.h to follow this coding style.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Idcc85eef31bb8c11766e834554bfab8b6ed35864

Fix: rcuhlist header: use parenthesis around macro parameters

The coding style followed across liburcu is to use parenthesis around
macro parameters when it would otherwise lead to unexpected results due
to priority of operators. Fix rcuhlist.h to follow this coding style.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I2f7988e96ce495d68960c5f1036aa6953d3ff53b

Fix: hlist header: use parenthesis around macro parameters

The coding style followed across liburcu is to use parenthesis around
macro parameters when it would otherwise lead to unexpected results due
to priority of operators. Fix hlist.h to follow this coding style.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I28425b620b7937f6b3a57d48d70ce097d0093e23

Fix: list.h: use parenthesis around macro parameters, caa_container_of()

The coding style followed across liburcu is to use parenthesis around
macro parameters when it would otherwise lead to unexpected results due
to priority of operators. Fix list.h to follow this coding style.

Use caa_container_of() for cds_list_entry rather than open-code the
pointer arithmetic.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I17052dc0418ad205cf262a6e5b91e591c37462cb

Fix: hlist iteration relies on undefined behavior

Comparing an offset from an object with NULL is undefined behavior
and the compiler may assume that this is never true.

This is indeed what is observed with gcc-10 miscompiling
cds_hlist_for_each_entry_rcu_2().

Fix this by introducing cds_hlist_entry_safe() rather than open-coding
the NULL check comparisons, and move cds_hlist_for_each_entry_2()
and cds_hlist_for_each_entry_safe_2() to this scheme as well.

Fixes: #1308
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ief3531cf04e54b6dae05eb28a6822adfa141fdeb

Fix: use __atomic_load() rather than atomic load explicit

Use __atomic_load (gcc extension) rather than atomic load explict
(C11/C++11) for rcu_dereference because it does not require the input
type to be _Atomic. This fixes a regression with clang introduced by
commit 380f4b19052 ("Fix: use atomic load memory_order_consume for
rcu_dereference on C11/C++11").

Note that the cmm_smp_read_barrier_depends is removed when using
__ATOMIC_CONSUME because their memory ordering effect is redundant.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Icd5f6040e0bd2167844a8d856ae5475ceef17123

Fix: use atomic load memory_order_consume for rcu_dereference on C11/C++11

Using volatile accesses for rcu_dereference may cause compiler LTO to
generate incorrectly ordered code starting from C11/C++11.

Link: https://lists.lttng.org/pipermail/lttng-dev/2021-April/029937.html
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: we used weak symbols not weak aliases

Remove the configure test for weak aliases since we don't use them and
they are not supported on macOs.

Change-Id: If245dfe02c9ec990e16e1a90983ba9d8f1eb9f4b
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: include 'sys/endian.h' on FreeBSD

We need to include 'sys/endian.h' on FreeBSD to use BYTE_ORDER.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I9f6e9d522e3857304fb9556098a775d1f0d35ef9

fix: warnings on non-Linux platforms

Add the relevent attributes in non-Linux wrapper code.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I0c50dc57f71804aa544350178793bdf280a667df

fix: HAVE_SCHED_SETAFFINITY is not defined

Use '#ifdef' instead of '#if' to test if HAVE_SCHED_SETAFFINITY is
defined. Both work but using '#if' on an undefined macro will generate a
warning with '-Wundef'.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ieb46ddab9ba033a5c552dbe78ac398cea0a641e8

configure: enable extended compiler warnings

Import the compiler warning flag detection system from Babeltrace and
enable extended compiler warnings.

Change-Id: Ia3ef4d37640fb3384dc76778ed88d0519f9b7e25
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

cleanup: explicitly mark unused parameters (-Wunused-parameter)

Add the 'unused' attribute to function parameters that are unused to
allow turning on -Wunused-parameter and distinguish unused parameters
that are actual errors.

Change-Id: Ie585e37f9d38718543a31aee2e7ab3428cdfd0a5
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: shadowed local variable (-Wshadow)

Rename local variables that are shadowed by global variables.

Change-Id: Ic60e880cb6e98d6111e6b747d9668731a156e4fa
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

cleanup: all functions have declarations (-Wmissing-prototypes)

Make sure that all non-static functions have a declaration.

Change-Id: Ie1596ad4ba876183862e51508c8bd7fc0451fc5e
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Import libtap from babeltrace

Import the fixes to our local copy of libtap from the babeltrace
repository. This will allow enabling stricter compiler warnings down the
line.

Change-Id: I557ad39345dfaf6a08219109a5790d1bf12abb78
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

cleanup: add 'noreturn' attribute to '_uatomic_link_error'

Tell the compiler that this function never returns, may help with
optimizations.

Change-Id: I07e4bdc5c83436e497db02394eccfbf44063f090
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: add missing 'S' to AC_CHECK_PROGS

AC_CHECK_PROG has a different behavior to AC_CHECK_PROGS and won't set
the proper variable without further arguments.

Change-Id: Ia20c16772a42bc21d7d518095a13f4ad574cb65d
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

README.md: Document supported Glibc version

Change-Id: I3be87d2db6be1f2a35bb2df7208b8a2d197b3d49
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

README: cleanup stale MacOS information

Change-Id: Ife4a3b79e26731242ee89e1d25638d3907e20434
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Bump version to 0.13.0-pre

Change-Id: Ic09dcbd766b3b915615b1bb10812e8fd86c4cf0b
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

configure: standardise include path

Use the same include setup as our other projects, set the default
includes globally in configure.ac in AM_CPPFLAGS.

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: Ia40344e22920bafca9ed34ea2867acf38a1807e3
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Remove glibc < 2.4 compat code for sched_setaffinity

Remove the rather large configure compat code for the version of
sched_setaffinity as present in glibc < 2.4.

Glibc 2.4 was released in 2006, we can safely assume nobody is still
building new systems based on an even older version.

Keep the normal sched_setaffinity detection and wrappers.

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: I62b1488849f88f56424f4d4ce570519d37c746c5
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

configure: regroup automake conditionals

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: I5be5e254670e2ca6c26564ab391ea1dbfea105cd
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Introduce AE_FEATURE to manage configure features

The new AE_FEATURE set of macros are wrappers over autoconf's
AC_ARG_ENABLE. The main objective is to make the m4sh code more readable
to the less seasoned autotools enthusiast among us and reduce the
duplication of code with its associated bugs.

The AE prefix was chosen to mean "Autotools EfficiOS" and is part of an
effort to standardize our custom macros across all our autotools based
projects.

Change-Id: Ief565473b38150fe2104492c6339bac73efba895
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

configure: regroup library checks

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: Iea3c5f5348426b7cbefabb60a7c9b33e179e6650
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

configure: regroup and expand C header and program checks

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: I74b5664782fa67df8a2350d90d6f03a16f930fef
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

configure: regroup and expand C compiler checks

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: I7d6f93c738334c6c0d9851924296a537cb076360
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

configure: host specific config

Align host specific configuration style with our other autotools
projects.

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: I413b4425f9027dfcce74b40292e13df604b602a3
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

tests: Move tap-driver.sh out of the autotools aux directory

We have made local modifications to this script, move it to the test
suite directory so it doesn't get overwritten by an updated version from
autotools.

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: I4bc0bdbff05d03d8e4c0f9dcda51cf6a6cf7fec4
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

configure: Set autotools baseline

Set autotools baseline to Autoconf >= 2.69 and Automake >= 1.12 and
enable error reporting.

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: I1f3487d7e610b3f6f9d710ef2d1d4b7a39d7dabb
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

configure: centralize version information

Centralise version information at the beginning of configure.ac to
improve readability.

This is part of an effort to standardise our autotools setup across
project to simplify maintenance.

Change-Id: I394c706f71885dbc6ad22f6d315d48702825fd81
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: exclude clang from GCC version blacklists

URCU_GCC_VERSION is used to blacklist specific GCC versions with known
bugs, clang also defines these macros to an equivalent GCC version it
claims to support, so exclude it.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Idf0980fddca6533313a3367601ddda8d8e13bfdf

aarch64: blacklist gcc prior to 5.1

Linux aarch64 requires GCC 5.1 or better because prior versions perform
unsafe access to deallocated stack.

Some Linux distributions may have backported the fix, but it was never
released into earlier upstream gcc versions.

Link: https://lwn.net/Articles/842122/
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Fix: configure: support Autoconf 2.70

The newly-released autoconf 2.70 introduces a number of breaking
changes [1] and is being rolled-out by some distros.

Amongst those changes, the AC_PROG_CC_STDC macro is marked as obsolete
and was merged into AC_PROG_CC, which we already use. On 2.70, this
results in a warning which we handle as an error.

A version check is added to invoke the AC_PROG_CC_STDC macro only when
running a pre-2.70 version of autoconf, fixing the issue.

Also, the AX_PTHREAD macro makes use of the $as_echo built-in shell
variable which no longer exists in 2.70. A patch was submitted to the
GNU Autoconf archive in March, but there have been no signs of life
given since then [2].

As such, our local copy is updated to the latest version and the patch
(which looks fairly straight-forward / safe) is applied. This should
minimize changes once we go back to an "official" version of the macro.

[1] https://lwn.net/Articles/839395/
[2] https://savannah.gnu.org/patch/?9906

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Id57ad87e63c2d398e3d8b81129f9b867b878e01f

Don't force a target and optimization level on ARMv7

We shouldn't force a specific target cpu for the compiler on ARMv7 but
let the system or the user choose it. If some of our code depends on a
specific target CPU features, it should be compile tested.

Also remove the default optimisation level of O1, it's potentially a
workaround to an early armv7 compiler performance problem and anyway
most builds will have an optimisation level flag set in the CFLAGS which
will override this one.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I1d1bb5cc0fa0be8f8b1d6a9ad7bf063809be1aef

Use DMB only on ARMv7

Remove the configure time CONFIG_RCU_ARM_HAVE_DMB option and replace it
by compile time detection based on the ARM ISA version. This makes sure
we unconditionnaly use the DMB instruction only on ARMv7 where it's part
of the baseline ISA.

This will change the behavior on ARMv6 platform that possibly have this
instruction but it was probably already broken since we use the 'ISH'
option which doesn't seem to be valid on this ISA.

This will also allow sharing headers in a multi-arch environment and
reduce the build system complexity.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I8e56ada55148d8e0f198c3d2e741ea414de5fef2

Blacklist GCC 4.4.0, 4.4.1 and 4.4.2 on ARM

GCC added __sync_synchronize() in 4.4.0 but it was broken on ARM until
4.4.3, see the GCC bug report for more details :

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42263

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I629e3c8b4baaccb34b2311e220f30d0ad8b69a19

Cleanup: Move ARM specific code to urcu/arch/arm.h

Change-Id: I3e17308c5ae985789a2ac8361e9c9e958ff7d656
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: bump tests thread limit to 4096

Machines with more than 128 CPUs are becomming more common. A
future-proof fix here would be to dynamically allocate the array, but in
the meantime bump the limit to 4096 to fix the problem on a 160 CPUs
ppc64el system where this was reported.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ib3cb5d8cb4515e6f626be33c2685fa38cb081782

fix: reorder x86 arch detection

Reorder the detection code from most specific to most generic as defines
for i386 can be present even when building for i686.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I81531b05318a0eaa9984075311828d87be7d46fc

fix: typo in futex syscall define check

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I59a654e381f3ad236a6d25c67316d04c84ddcded

Compile time futex syscall detection

The futex syscall availability is detected at configure time using a
simple compile test. Replace this with compile time detection using the
same test. This would allow sharing headers in a multi-arch environment
and reduce the build system complexity.

Change-Id: Ief709429e8908d0fd2d268d42f4a89d9fc14b91b
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Static arch and uatomic headers

Replace the somewhat hackish symlinking of architecture specific headers
at configure time with compile time detection using compiler defines.
This would allow sharing headers in a multi-arch environment and reduce
the build system complexity.

Change-Id: I4900a18dab70bb0e51d1a8500581a445acd44cdf
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Add git-review config

Add .gitreview for contributors wishing to use gerrit for patch
reviews.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Change-Id: I7868b3fc3162246298f24bd90ac1a3bcf6083eb6
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

cleanup: Improve wording of CONFIG_RCU_DEBUG description

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: explicitly include urcu/config.h in files using CONFIG_RCU_ defines

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Fix typo in README.md

Signed-off-by: Shuo Wang <wangshuo47@huawei.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

fix: add -lurcu-common to pkg-config libs for each flavor

The urcu-common library contains common code like the write-free queue
and compat code, each urcu flavor library is dynamicly linked with it.

Most but not all toolchains will automatically link an executable with a
transitive depency of an explicitly linked library if said binary uses a
symbol from the transitive dependency.

Since this behavior is not present in all toolchains, add
'-lurcu-common' to the 'Libs' field of each flavors pkg-config file so
that executables using symbols from urcu-common can be reliably linked
using pkg-config.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

call_rcu: Fix race between rcu_barrier() and call_rcu_data_free()

The current code can lose RCU callbacks at shutdown time, which can
result in hangs.  This lossage can happen as follows:

o       A thread invokes call_rcu_data_free(), which executes up through
        the wake_call_rcu_thread().  At this point, the call_rcu_data
        structure has been drained of callbacks, but is still on the
        call_rcu_data_list.  Note that this thread does not hold the
        call_rcu_mutex.

o       Another thread invokes rcu_barrier(), which traverses the
        call_rcu_data_list under the protection of call_rcu_mutex,
        a list which still includes the above newly drained structure.
        This thread therefore adds a callback to the newly drained
        call_rcu_data structure.  It then releases call_rcu_mutex and
        enters a mystifying loop that does futex stuff.

o       The first thread finishes executing call_rcu_data_free(),
        which acquires call_rcu_mutex just long enough to remove the
        newly drained call_rcu_data structure from call_rcu_data_list.
        Which causes one of the rcu_barrier() invocation's callbacks to
        be leaked.

o       The second thread's rcu_barrier() invocation never returns
        resulting in a hang.

This commit therefore changes call_rcu_data_free() to acquire
call_rcu_mutex before checking the call_rcu_data structure for callbacks.
In the case where there are no callbacks, call_rcu_mutex is held across
both the check and the removal from call_rcu_data_list, thus preventing
rcu_barrier() from adding a callback in the meantime.  In the case where
there are callbacks, call_rcu_mutex must be momentarily dropped across
the call to get_default_call_rcu_data(), which can itself acquire
call_rcu_mutex.  This momentary drop is not a problem because any
callbacks that rcu_barrier() might queue during that period of time will
be moved to the default call_rcu_data structure, and the lock will be
held across the full time including moving those callbacks and removing
the call_rcu_data structure that was passed into call_rcu_data_free()
from call_rcu_data_list.

With this fix, a several-hundred-CPU test successfully completes more
than 5,000 executions.  Without this fix, it fails within a few tens
of executions.  Although the failures happen more quickly on larger
systems, in theory this could happen on a single-CPU system, courtesy
of preemption.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: <lttng-dev@lists.lttng.org>
Cc: <linux-kernel@vger.kernel.org>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Cleanup: tls-compat.h: add parentheses around expression (coding style)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Fix: tls-compat.h exposes compiler-dependent public configuration

Exposing the storage class chosen by ax_tls.m4 in a public header is
a bad idea, because if a recent gcc is used when configuring
liburcu, thus detecting C11, it will choose _Thread_local. Then, if an
external project uses urcu/tls-compat.h with an older gcc (e.g. 4.8),
it will fail to build, because that storage class is unknown, and
__thread should be used instead.

Therefore, use a preprocessor conditional on __cplusplus to detect C++11
(and use thread_local). Else, the STDC version is used to select
_Thread_local. Else check if _MSC_VER is defined to select
__declspec(thread), or else rely on __thread as fallback.

Remove ax_tls.m4 because it is now unused.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Fix: tap array subscript has type char warning

On architectures where "char" is signed, it should be cast to unsigned
char before being passed as parameter to isdigit or isspace. Based on
their man page:

       These  functions  check  whether  c,  which  must  have the value of an
       unsigned char or EOF, falls into a certain character class according to
       the  specified  locale.

Passing a signed char as parameter is invalid if the values fall into
the negative range of the signed char.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Version 0.12.0

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

tls-compat.h: introduce DEFINE_URCU_TLS_INIT

DEFINE_URCU_TLS() cannot be used in this way for !CONFIG_RCU_TLS:

  DEFINE_URCU_TLS(ino_t, cached_net_ns) = NS_INO_UNINITIALIZED;

Introduce a new DEFINE_URCU_TLS_INIT which allows expressing a nonzero
intial value:

  DEFINE_URCU_TLS_INIT(ino_t, cached_net_ns, NS_INO_UNINITIALIZED);

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Use _umtx_op for futex on FreeBSD

Tested with "make check", "make regtest" and a knotd slave.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>