[Natty/SRU][PATCH] ipc/sem.c: fix race with concurrent semtimedop() timeouts and IPC_RMID

[Herton R. Krzesinski]

SRU justification
=================

Impact
------
Kernel crash, due to race explained in upstream bug report:
https://bugzilla.kernel.org/show_bug.cgi?id=27142
In practice likely to happen on a highly loaded webserver

Fix
---
Upstream commit d694ad62bf539dbb20a0899ac2a954555f9e4a83

Testcase
--------
https://bugzilla.kernel.org/attachment.cgi?id=66162
I'll attach to this bug as well.
- Build with gcc -o timedrm timedrm.cpp -lpthread
- Run with "test 250", sometimes you have to run more than one time to get the
oops, but it's very easy to get the crash.

Note: only needed for natty. The problem affects 2.6.35 and later, but
we already got fixes for Maverick/Oneiric through stable, Precise has
the fix in also.

-- 
[]'s
Herton