[Bug 90492] Xorg unresponsive under heavy system-load

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90492

--- Comment #1 from Chris Wilson <chris at chris-wilson.co.uk> ---
You ran out of memory (including swap). The kernel cannot execute the GPU
commands due to memory exhaustion and that eventually lands in an untrapped
SIGBUS. The segfault is a bug elsewhere in the xserver. It is unresponsive due
to the amount of swap thrashing...

For example, the first Xorg.0.log, the crash is due to not being able to page
in a library from disk. The second didn't have enough memory even to do symbol
lookups in the backtrace. The third is a segfault during client shutdown, but
it is not clear where. The last one is the only one that looks like the ddx
should have prevented but didn't (the ddx is aware that accessing a mmap() may
cause a SIGBUS due to oom and tries to trap them) -- however, symbol lookup
failed. So for what it is worth, I added a few missing traps around pixman_fill
based on the Xorg.0.log you reported on irc:

commit 335ac8742e9eadcdf8f087b24f84c7df0fda31c0
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Sun May 17 08:53:45 2015 +0100

    sna: Wrap CPU access for composite operations with sigtrap

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