On Thu, Sep 04, 2014 at 10:39:31AM +0200, Daniel Vetter wrote: > On Thu, Sep 04, 2014 at 10:34:13AM +0200, Daniel Vetter wrote: > > On Wed, Sep 03, 2014 at 02:47:21PM -0300, Paulo Zanoni wrote: > > > From: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx> > > > > > > If we don't reset exit_handler_count before forking, we may have a > > > case where the forked process is killed before it even does > > > "exit_handler_count = 0": in that case, it is still finishing forking. > > > When that happens, we may end up calling our exit handlers. On the > > > specific bug I'm investigating, we call igt_reset_connnectors(), which > > > ends up in a deadlock inside malloc_atfork. If we attach gdb to the > > > forked process and get a backtrace, we have: > > > > > > (gdb) bt > > > 0 __lll_lock_wait_private () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95 > > > 1 0x00007f15634d36bf in _L_lock_10524 () from /lib/x86_64-linux-gnu/libc.so.6 > > > 2 0x00007f15634d12ef in malloc_atfork (sz=139729840351352, caller=<optimized out>) at arena.c:181 > > > 3 0x00007f15640466a1 in drmMalloc () from /usr/lib/x86_64-linux-gnu/libdrm.so.2 > > > 4 0x00007f1564049ad7 in drmModeGetResources () from /usr/lib/x86_64-linux-gnu/libdrm.so.2 > > > 5 0x0000000000408f84 in igt_reset_connectors () at igt_kms.c:1656 > > > 6 0x00000000004092dc in call_exit_handlers (sig=15) at igt_core.c:1130 > > > 7 fatal_sig_handler (sig=15) at igt_core.c:1154 > > > 8 <signal handler called> > > > 9 0x00007f15634cce60 in ptmalloc_unlock_all2 () at arena.c:298 > > > 10 0x00007f156350ca3f in __libc_fork () at ../nptl/sysdeps/unix/sysv/linux/x86_64/../fork.c:188 > > > 11 0x000000000040a029 in __igt_fork_helper (proc=proc@entry=0x610fc4 <signal_helper>) at igt_core.c:910 > > > 12 0x000000000040459d in igt_fork_signal_helper () at igt_aux.c:110 > > > 13 0x0000000000402ab7 in __real_main63 () at bug.c:76 > > > 14 0x000000000040296e in main (argc=<optimized out>, argv=<optimized out>) at bug.c:63 But note that this means that igt_reset_connectors is *not* signal safe and needs to be rewritten in order for it to work as an exit handler. Otherwise this bug will just keep on reoccurring. -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
