The attached logfile shows a thread/data race (mozilla-central revision beddd6d4bcdf) detected by TSan (ThreadSanitizer). Typically, races reported by TSan are not false positives, but it is possible that the race is benign. Even in this case though, we should try to come up with a fix unless this would cause inacceptable performance issues. Also note that seemingly benign races can possibly be harmful (also depending on the compiler and the architecture) [1]. If the bug cannot be fixed, then this bug should be used to either make a compile-time annotation for blacklisting or add an entry to the runtime blacklist. [1] http://software.intel.com/en-us/blogs/2013/01/06/benign-data-races-what-could-possibly-go-wrong

This looks like the race is coming from glib, but I cannot tell if we're using it somehow wrong (e.g. calling the some glib methods fro multiple threads in an unsafe way).

Is there any way to get better stack straces? The log file may be skipping frames where functions are inlined. Debug info contains the necessary info to unwind inlined frames, and addr2line can interpret this, but even the return addresses don't look right. #1 g_rec_mutex_impl_new /build/buildd/glib2.0-2.32.1/./glib/gthread-posix.c:272 (libglib-2.0.so.0+0x000000083151) #2 XREMain::XRE_main(int, char**, nsXREAppData const*) /srv/repos/browser/mozilla-central/toolkit/xre/nsAppRunner.cpp:4029 (libxul.so+0x00000085c33a) #3 slab_allocator_alloc_chunk /build/buildd/glib2.0-2.32.1/./glib/gslice.c:1300 (libglib-2.0.so.0+0x00000001a0c9) #4 XREMain::XRE_main(int, char**, nsXREAppData const*) /srv/repos/browser/mozilla-central/toolkit/xre/nsAppRunner.cpp:4029 (libxul.so+0x00000085c33a) #1 g_system_thread_new /build/buildd/glib2.0-2.32.1/./glib/gthread-posix.c:1116 (libglib-2.0.so.0+0x000000083a7e) #2 XREMain::XRE_main(int, char**, nsXREAppData const*) /srv/repos/browser/mozilla-central/toolkit/xre/nsAppRunner.cpp:4029 (libxul.so+0x00000085c33a) I can't imagine how these three different functions would all return to the same instruction pointer position.