> Date: Fri, 9 Apr 2021 07:09:06 +1000 > From: Jonathan Matthew <jonat...@d14n.org> > > On Thu, Apr 08, 2021 at 10:24:06AM +0200, Martin Pieuchot wrote: > > firefox often crash when somebody else connects to the jitsi I'm in. > > The trace looks like a stack exhaustion, see below. > > > > Does this ring a bell? > > > > #530 <signal handler called> > > #531 pthread_setschedparam (thread=0x0, policy=1, param=0x2ade5ca1df0) > > at /usr/src/lib/librthread/rthread_sched.c:56 > > #532 0x000002ae65f9f016 in > > rtc::PlatformThread::SetPriority(rtc::ThreadPriority) () from > > /usr/local/lib/firefox/libxul.so.101.0 > > #533 0x000002ae65f9ed75 in rtc::PlatformThread::Run() () > > from /usr/local/lib/firefox/libxul.so.101.0 > > #534 0x000002ae65f9ead9 in rtc::PlatformThread::StartThread(void*) () > > from /usr/local/lib/firefox/libxul.so.101.0 > > #535 0x000002ade9d4df51 in _rthread_start (v=<optimized out>) > > at /usr/src/lib/librthread/rthread.c:96 > > #536 0x000002ad9c2ec3da in __tfork_thread () > > at /usr/src/lib/libc/arch/amd64/sys/tfork_thread.S:84 > > This looks like, at least with our pthreads implementation, libwebrtc has a > race between the newly created thread and the thread creating it. > > The creating thread stores the thread handle in thread_ here: > https://github.com/mozilla/gecko-dev/blob/master/third_party/libwebrtc/webrtc/rtc_base/platform_thread.cc#L186 > > and the new thread uses it here: > https://github.com/mozilla/gecko-dev/blob/master/third_party/libwebrtc/webrtc/rtc_base/platform_thread.cc#L363 > which is called as almost the first thing the new thread does. > > Our pthread_create() only stores the pthread handle into the supplied > address after __tfork_thread() returns, by which time the new thread > could already be running.
Right. POSIX isn't very explicit about this, but it does state that the thread ID is stored upon successful completion. So I don't think portable code can rely on that until pthread_create() has returned. Using pthread_self() in the pthread_setschedparam() call will probably help. But if PlatformThread::GetThreadRef() gets called early on in the thread, there will still be a race. Setting thread_ at the start of PlatformThread::Run() would be better.
