From: hewenliang Date: Tue, 17 Sep 2019 14:59:18 +0000 (-0400) Subject: Fix: rculfhash worker needs to unblock to SIGRCU X-Git-Tag: v0.10.3~5 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=22e3a77f65d53b84dbe653fa6cb83181cafe2482;p=userspace-rcu.git Fix: rculfhash worker needs to unblock to SIGRCU In urcu-signal flavor, call_rcu_thread calls synchronize_rcu which will send SIGRCU signal to all registed threads, and then loops to wait need_mb to be cleared. However, the registed workqueue_thread does not process the SIGRCU signal, and never clear the need_mb. Based on above, call_rcu_thread and workqueue_thread will wait forever for completion of the grace period: call_rcu_thread which holds the rcu_registry_lock, waits for workqueue_thread to do cmm_smp_mb. While workqueue thread never does cmm_smp_mb because of signal blocking, and it will eventually wait to get rcu_registry_lock in do_resize_cb. The phenomenon is as follows, which is easy to be triggered: (gdb) t 2 [Switching to thread 2 (Thread 0xffff83c3b080 (LWP 27116))] 0 0x0000ffff845296c4 in poll () from /lib64/libc.so.6 (gdb) bt 0 0x0000ffff845296c4 in poll () from /lib64/libc.so.6 1 0x0000ffff8461b93c in force_mb_all_readers () at urcu.c:241 2 0x0000ffff8461c748 in smp_mb_master () at urcu.c:249 3 urcu_signal_synchronize_rcu () at urcu.c:445 4 0x0000ffff8461d004 in call_rcu_thread at urcu-call-rcu-impl.h:364 5 0x0000ffff845eb8bc in start_thread () from /lib64/libpthread.so.0 6 0x0000ffff845335cc in thread_start () from /lib64/libc.so.6 (gdb) t 3 [Switching to thread 3 (Thread 0xffff8443c080 (LWP 27191))] 0 0x0000ffff845f51c4 in __lll_lock_wait () from /lib64/libpthread.so.0 (gdb) bt 0 0x0000ffff845f51c4 in __lll_lock_wait () from /lib64/libpthread.so.0 1 0x0000ffff845ee048 in pthread_mutex_lock () from /lib64/libpthread.so.0 2 0x0000ffff8461b814 in mutex_lock ( ) at urcu.c:157 3 0x0000ffff8461b9e4 in urcu_signal_unregister_thread () at urcu.c:564 4 0x0000ffff8463e62c in do_resize_cb (work=0x11e2e790) at rculfhash.c:2042 5 0x0000ffff8463c940 in workqueue_thread (arg=0x11e1d260) at workqueue.c:228 6 0x0000ffff845eb8bc in start_thread () from /lib64/libpthread.so.0 7 0x0000ffff845335cc in thread_start () from /lib64/libc.so.6 So we should not block SIGRCU in workqueue thread to avoid blocking forever in the grace period awaiting on the worker thread when using urcu-signal flavor. Signed-off-by: hewenliang Co-developed-by: Mathieu Desnoyers Signed-off-by: Mathieu Desnoyers Cc: Paul E. McKenney --- diff --git a/include/Makefile.am b/include/Makefile.am index dcdf304..9e93430 100644 --- a/include/Makefile.am +++ b/include/Makefile.am @@ -11,6 +11,7 @@ nobase_dist_include_HEADERS = urcu/compiler.h urcu/hlist.h urcu/list.h \ urcu/static/urcu.h urcu/static/urcu-pointer.h \ urcu/static/urcu-qsbr.h urcu/static/wfcqueue.h \ urcu/static/wfqueue.h urcu/static/wfstack.h \ + urcu/static/urcu-signal-nr.h \ urcu/tls-compat.h urcu/debug.h # Don't distribute generated headers diff --git a/include/urcu/static/urcu-signal-nr.h b/include/urcu/static/urcu-signal-nr.h new file mode 100644 index 0000000..a488f3a --- /dev/null +++ b/include/urcu/static/urcu-signal-nr.h @@ -0,0 +1,42 @@ +#ifndef _STATIC_URCU_SIGNAL_NR_H +#define _STATIC_URCU_SIGNAL_NR_H + +/* + * static/urcu-signal-nr.h + * + * Userspace RCU header. + * + * Copyright (c) 2009 Mathieu Desnoyers + * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + * + * IBM's contributions to this file may be relicensed under LGPLv2 or later. + */ + +/* + * The signal number used by the RCU library can be overridden with + * -DSIGRCU= when compiling the library. + * Provide backward compatibility for liburcu 0.3.x SIGURCU. + */ +#ifdef SIGURCU +#define SIGRCU SIGURCU +#endif + +#ifndef SIGRCU +#define SIGRCU SIGUSR1 +#endif + +#endif /* _STATIC_URCU_SIGNAL_NR_H */ diff --git a/include/urcu/static/urcu.h b/include/urcu/static/urcu.h index 20fc864..0b5ce92 100644 --- a/include/urcu/static/urcu.h +++ b/include/urcu/static/urcu.h @@ -43,6 +43,7 @@ #include #include #include +#include #ifdef __cplusplus extern "C" { @@ -61,19 +62,6 @@ extern "C" { * This is required to permit relinking with newer versions of the library. */ -/* - * The signal number used by the RCU library can be overridden with - * -DSIGRCU= when compiling the library. - * Provide backward compatibility for liburcu 0.3.x SIGURCU. - */ -#ifdef SIGURCU -#define SIGRCU SIGURCU -#endif - -#ifndef SIGRCU -#define SIGRCU SIGUSR1 -#endif - enum rcu_state { RCU_READER_ACTIVE_CURRENT, RCU_READER_ACTIVE_OLD, diff --git a/src/rculfhash.c b/src/rculfhash.c index fed33e4..17d3143 100644 --- a/src/rculfhash.c +++ b/src/rculfhash.c @@ -273,6 +273,7 @@ #include #include #include +#include #include #include #include @@ -2106,18 +2107,24 @@ static struct urcu_atfork cds_lfht_atfork = { .after_fork_child = cds_lfht_after_fork_child, }; -/* Block all signals to ensure we don't disturb the application. */ +/* + * Block all signals for the workqueue worker thread to ensure we don't + * disturb the application. The SIGRCU signal needs to be unblocked for + * the urcu-signal flavor. + */ static void cds_lfht_worker_init(struct urcu_workqueue *workqueue, void *priv) { int ret; sigset_t mask; - /* Block signal for entire process, so only our thread processes it. */ ret = sigfillset(&mask); if (ret) urcu_die(errno); - ret = pthread_sigmask(SIG_BLOCK, &mask, NULL); + ret = sigdelset(&mask, SIGRCU); + if (ret) + urcu_die(ret); + ret = pthread_sigmask(SIG_SETMASK, &mask, NULL); if (ret) urcu_die(ret); }