Phase 1 of deprecating liburcu-signal

The first phase of liburcu-signal deprecation consists of implementing
it in term of liburcu-mb. In other words, liburcu-signal is identical to
liburcu-mb at the exception of the function symbols and public header
files.

This is done by:

  1) Removing the RCU_SIGNAL specific code in urcu.c

  2) Making the RCU_MB specific code also specific to RCU_SIGNAL in
  urcu.c

  3) Rewriting _urcu_signal_read_unlock_update_and_wakeup to use a
  atomic store with CMM_SEQ_CST instead of a store CMM_RELAXED with
  cmm_barrier() around it. We could keep the explicit barriers, but that
  would require to add some cmm_annotate annotations. Therefore, to be
  less intrusive in a public header file, simply use the CMM_SEQ_CST
  like for the mb flavor.

Change-Id: Ie406f7df2f47da0a9f464df94b968ad9204821f3
Signed-off-by: Olivier Dion <odion@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/README.md b/README.md
index d7966a2c54dbbad4eaf92a5e01b8d99abd7e6451..58db299018deb07f36fbdd1bad863ed35f82b3e0 100644 (file)
--- a/README.md
+++ b/README.md
@@ -220,9 +220,10 @@ results in slower reads.
   1. `#include <urcu/urcu-signal.h>`
   2. Link the application with `-lurcu-signal`
 
-Version of the library that requires a signal, typically `SIGUSR1`. Can
-be overridden with `-DSIGRCU` by modifying `Makefile.build.inc`.
-
+NOTE: The `liburcu-signal` flavor is *deprecated* and will be removed in the
+future. It is now identical to `liburcu-mb` at the exception of the symbols and
+public header files. It is therefore slower than previous versions. Users are
+encouraged to migrate to the `liburcu-memb` flavor.
 
 ### Usage of `liburcu-bp`
 

diff --git a/include/urcu/static/urcu-signal.h b/include/urcu/static/urcu-signal.h
index baee2298c9232e34b16e5ca6a0e0923fb0fd7daf..0f78ac0d1e1378d8a2898ce27ae424212747d9ce 100644 (file)
--- a/include/urcu/static/urcu-signal.h
+++ b/include/urcu/static/urcu-signal.h
@@ -95,13 +95,14 @@ static inline void _urcu_signal_read_lock(void)
  */
 static inline void _urcu_signal_read_unlock_update_and_wakeup(unsigned long tmp)
 {
+       unsigned long *ctr = &URCU_TLS(urcu_signal_reader).ctr;
+
        if (caa_likely((tmp & URCU_GP_CTR_NEST_MASK) == URCU_GP_COUNT)) {
-               cmm_barrier();
-               _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp - URCU_GP_COUNT);
-               cmm_barrier();
+               uatomic_store(ctr, tmp - URCU_GP_COUNT, CMM_SEQ_CST);
                urcu_common_wake_up_gp(&urcu_signal_gp);
-       } else
-               _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp - URCU_GP_COUNT);
+       } else {
+               uatomic_store(ctr, tmp - URCU_GP_COUNT, CMM_RELAXED);
+       }
 }
 
 /*

diff --git a/src/urcu.c b/src/urcu.c
index 76c8720c288b5d5ce52eacdd58714126513645c4..984e929f78c54d9908660fb87adf62b4017a446e 100644 (file)
--- a/src/urcu.c
+++ b/src/urcu.c
@@ -86,20 +86,12 @@ int urcu_memb_has_sys_membarrier = 0;
 void __attribute__((constructor)) rcu_init(void);
 #endif
 
-#ifdef RCU_MB
+#if defined(RCU_MB) || defined(RCU_SIGNAL)
 void rcu_init(void)
 {
 }
 #endif
 
-#ifdef RCU_SIGNAL
-static int init_done;
-
-void __attribute__((constructor)) rcu_init(void);
-
-static DEFINE_URCU_TLS(int, rcu_signal_was_blocked);
-#endif
-
 void __attribute__((destructor)) rcu_exit(void);
 static void urcu_call_rcu_exit(void);
 
@@ -179,62 +171,13 @@ static void smp_mb_master(void)
 }
 #endif
 
-#ifdef RCU_MB
+#if defined(RCU_MB) || defined(RCU_SIGNAL)
 static void smp_mb_master(void)
 {
        cmm_smp_mb();
 }
 #endif
 
-#ifdef RCU_SIGNAL
-static void force_mb_all_readers(void)
-{
-       struct urcu_reader *index;
-
-       /*
-        * Ask for each threads to execute a cmm_smp_mb() so we can consider the
-        * compiler barriers around rcu read lock as real memory barriers.
-        */
-       if (cds_list_empty(&registry))
-               return;
-       /*
-        * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
-        * a cache flush on architectures with non-coherent cache. Let's play
-        * safe and don't assume anything : we use cmm_smp_mc() to make sure the
-        * cache flush is enforced.
-        */
-       cds_list_for_each_entry(index, &registry, node) {
-               CMM_STORE_SHARED(index->need_mb, 1);
-               pthread_kill(index->tid, SIGRCU);
-       }
-       /*
-        * Wait for sighandler (and thus mb()) to execute on every thread.
-        *
-        * Note that the pthread_kill() will never be executed on systems
-        * that correctly deliver signals in a timely manner.  However, it
-        * is not uncommon for kernels to have bugs that can result in
-        * lost or unduly delayed signals.
-        *
-        * If you are seeing the below pthread_kill() executing much at
-        * all, we suggest testing the underlying kernel and filing the
-        * relevant bug report.  For Linux kernels, we recommend getting
-        * the Linux Test Project (LTP).
-        */
-       cds_list_for_each_entry(index, &registry, node) {
-               while (CMM_LOAD_SHARED(index->need_mb)) {
-                       pthread_kill(index->tid, SIGRCU);
-                       (void) poll(NULL, 0, 1);
-               }
-       }
-       cmm_smp_mb();   /* read ->need_mb before ending the barrier */
-}
-
-static void smp_mb_master(void)
-{
-       force_mb_all_readers();
-}
-#endif /* #ifdef RCU_SIGNAL */
-
 /*
  * synchronize_rcu() waiting. Single thread.
  * Always called with rcu_registry lock held. Releases this lock and
@@ -243,9 +186,7 @@ static void smp_mb_master(void)
 static void wait_gp(void)
 {
        /*
-        * Read reader_gp before read futex. smp_mb_master() needs to
-        * be called with the rcu registry lock held in RCU_SIGNAL
-        * flavor.
+        * Read reader_gp before read futex.
         */
        smp_mb_master();
        /* Temporarily unlock the registry lock. */
@@ -535,52 +476,8 @@ int rcu_read_ongoing(void)
        return _rcu_read_ongoing();
 }
 
-#ifdef RCU_SIGNAL
-/*
- * Make sure the signal used by the urcu-signal flavor is unblocked
- * while the thread is registered.
- */
-static
-void urcu_signal_unblock(void)
-{
-       sigset_t mask, oldmask;
-       int ret;
-
-       ret = sigemptyset(&mask);
-       urcu_posix_assert(!ret);
-       ret = sigaddset(&mask, SIGRCU);
-       urcu_posix_assert(!ret);
-       ret = pthread_sigmask(SIG_UNBLOCK, &mask, &oldmask);
-       urcu_posix_assert(!ret);
-       URCU_TLS(rcu_signal_was_blocked) = sigismember(&oldmask, SIGRCU);
-}
-
-static
-void urcu_signal_restore(void)
-{
-       sigset_t mask;
-       int ret;
-
-       if (!URCU_TLS(rcu_signal_was_blocked))
-               return;
-       ret = sigemptyset(&mask);
-       urcu_posix_assert(!ret);
-       ret = sigaddset(&mask, SIGRCU);
-       urcu_posix_assert(!ret);
-       ret = pthread_sigmask(SIG_BLOCK, &mask, NULL);
-       urcu_posix_assert(!ret);
-}
-#else
-static
-void urcu_signal_unblock(void) { }
-static
-void urcu_signal_restore(void) { }
-#endif
-
 void rcu_register_thread(void)
 {
-       urcu_signal_unblock();
-
        URCU_TLS(rcu_reader).tid = pthread_self();
        urcu_posix_assert(URCU_TLS(rcu_reader).need_mb == 0);
        urcu_posix_assert(!(URCU_TLS(rcu_reader).ctr & URCU_GP_CTR_NEST_MASK));
@@ -600,8 +497,6 @@ void rcu_unregister_thread(void)
        URCU_TLS(rcu_reader).registered = 0;
        cds_list_del(&URCU_TLS(rcu_reader).node);
        mutex_unlock(&rcu_registry_lock);
-
-       urcu_signal_restore();
 }
 
 #ifdef RCU_MEMBARRIER
@@ -652,57 +547,6 @@ void rcu_init(void)
 }
 #endif
 
-#ifdef RCU_SIGNAL
-static void sigrcu_handler(int signo __attribute__((unused)),
-               siginfo_t *siginfo __attribute__((unused)),
-               void *context __attribute__((unused)))
-{
-       /*
-        * Executing this cmm_smp_mb() is the only purpose of this signal handler.
-        * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
-        * executed on.
-        */
-       cmm_smp_mb();
-       _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
-       cmm_smp_mb();
-}
-
-/*
- * rcu_init constructor. Called when the library is linked, but also when
- * reader threads are calling rcu_register_thread().
- * Should only be called by a single thread at a given time. This is ensured by
- * holing the rcu_registry_lock from rcu_register_thread() or by running
- * at library load time, which should not be executed by multiple
- * threads nor concurrently with rcu_register_thread() anyway.
- */
-void rcu_init(void)
-{
-       struct sigaction act;
-       int ret;
-
-       if (init_done)
-               return;
-       init_done = 1;
-
-       act.sa_sigaction = sigrcu_handler;
-       act.sa_flags = SA_SIGINFO | SA_RESTART;
-       sigemptyset(&act.sa_mask);
-       ret = sigaction(SIGRCU, &act, NULL);
-       if (ret)
-               urcu_die(errno);
-}
-
-/*
- * Don't unregister the SIGRCU signal handler anymore, because
- * call_rcu threads could still be using it shortly before the
- * application exits.
- * Assertion disabled because call_rcu threads are now rcu
- * readers, and left running at exit.
- * urcu_posix_assert(cds_list_empty(&registry));
- */
-
-#endif /* #ifdef RCU_SIGNAL */
-
 void rcu_exit(void)
 {
        urcu_call_rcu_exit();