From 68a9398261ca38979bbc2b7c89ed5bb044ccc9e6 Mon Sep 17 00:00:00 2001 From: linzhecheng Date: Tue, 28 Nov 2017 12:46:56 +0800 Subject: [PATCH] qemu-thread: fix races on threads that exit very quickly If we create a thread with QEMU_THREAD_DETACHED mode, QEMU may get a segfault with low probability. The backtrace is: #0 0x00007f46c60291d7 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56 #1 0x00007f46c602a8c8 in __GI_abort () at abort.c:90 #2 0x00000000008543c9 in PAT_abort () #3 0x000000000085140d in patchIllInsHandler () #4 #5 pthread_detach (th=139933037614848) at pthread_detach.c:50 #6 0x0000000000829759 in qemu_thread_create (thread=thread@entry=0x7ffdaa8205e0, name=name@entry=0x94d94a "io-task-worker", start_routine=start_routine@entry=0x7eb9a0 , arg=arg@entry=0x3f5cf70, mode=mode@entry=1) at util/qemu_thread_posix.c:512 #7 0x00000000007ebc96 in qio_task_run_in_thread (task=0x31db2c0, worker=worker@entry=0x7e7e40 , opaque=0xcd23380, destroy=0x7f1180 ) at io/task.c:141 #8 0x00000000007e7f33 in qio_channel_socket_connect_async (ioc=ioc@entry=0x626c0b0, addr=, callback=callback@entry=0x55e080 , opaque=opaque@entry=0x42862c0, destroy=destroy@entry=0x0) at io/channel_socket.c:194 #9 0x000000000055bdd1 in socket_reconnect_timeout (opaque=0x42862c0) at qemu_char.c:4744 #10 0x00007f46c72483b3 in g_timeout_dispatch () from /usr/lib64/libglib-2.0.so.0 #11 0x00007f46c724799a in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0 #12 0x000000000076c646 in glib_pollfds_poll () at main_loop.c:228 #13 0x000000000076c6eb in os_host_main_loop_wait (timeout=348000000) at main_loop.c:273 #14 0x000000000076c815 in main_loop_wait (nonblocking=nonblocking@entry=0) at main_loop.c:521 #15 0x000000000056a511 in main_loop () at vl.c:2076 #16 0x0000000000420705 in main (argc=, argv=, envp=) at vl.c:4940 The cause of this problem is a glibc bug; for more information, see https://sourceware.org/bugzilla/show_bug.cgi?id=19951. The solution for this bug is to use pthread_attr_setdetachstate. There is a similar issue with pthread_setname_np, which is moved from creating thread to created thread. Signed-off-by: linzhecheng Message-Id: <20171128044656.10592-1-linzhecheng@huawei.com> Reviewed-by: Fam Zheng [Simplify the code by removing qemu_thread_set_name, and free the arguments before invoking the start routine. - Paolo] Signed-off-by: Paolo Bonzini --- util/qemu-thread-posix.c | 61 ++++++++++++++++++++++++++++------------ 1 file changed, 43 insertions(+), 18 deletions(-) diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c index 7306475899..959a57079f 100644 --- a/util/qemu-thread-posix.c +++ b/util/qemu-thread-posix.c @@ -479,15 +479,29 @@ static void __attribute__((constructor)) qemu_thread_atexit_init(void) } -/* Attempt to set the threads name; note that this is for debug, so - * we're not going to fail if we can't set it. - */ -static void qemu_thread_set_name(QemuThread *thread, const char *name) -{ #ifdef CONFIG_PTHREAD_SETNAME_NP - pthread_setname_np(thread->thread, name); -#endif +typedef struct { + void *(*start_routine)(void *); + void *arg; + char *name; +} QemuThreadArgs; + +static void *qemu_thread_start(void *args) +{ + QemuThreadArgs *qemu_thread_args = args; + void *(*start_routine)(void *) = qemu_thread_args->start_routine; + void *arg = qemu_thread_args->arg; + + /* Attempt to set the threads name; note that this is for debug, so + * we're not going to fail if we can't set it. + */ + pthread_setname_np(pthread_self(), qemu_thread_args->name); + g_free(qemu_thread_args->name); + g_free(qemu_thread_args); + return start_routine(arg); } +#endif + void qemu_thread_create(QemuThread *thread, const char *name, void *(*start_routine)(void*), @@ -502,23 +516,34 @@ void qemu_thread_create(QemuThread *thread, const char *name, error_exit(err, __func__); } + if (mode == QEMU_THREAD_DETACHED) { + pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED); + } + /* Leave signal handling to the iothread. */ sigfillset(&set); pthread_sigmask(SIG_SETMASK, &set, &oldset); - err = pthread_create(&thread->thread, &attr, start_routine, arg); + +#ifdef CONFIG_PTHREAD_SETNAME_NP + if (name_threads) { + QemuThreadArgs *qemu_thread_args; + qemu_thread_args = g_new0(QemuThreadArgs, 1); + qemu_thread_args->name = g_strdup(name); + qemu_thread_args->start_routine = start_routine; + qemu_thread_args->arg = arg; + + err = pthread_create(&thread->thread, &attr, + qemu_thread_start, qemu_thread_args); + } else +#endif + { + err = pthread_create(&thread->thread, &attr, + start_routine, arg); + } + if (err) error_exit(err, __func__); - if (name_threads) { - qemu_thread_set_name(thread, name); - } - - if (mode == QEMU_THREAD_DETACHED) { - err = pthread_detach(thread->thread); - if (err) { - error_exit(err, __func__); - } - } pthread_sigmask(SIG_SETMASK, &oldset, NULL); pthread_attr_destroy(&attr);