The case of the overly anonymous anon_vma
Apr 27, 2010, 06:03 (0 Talkback[s])
(Other stories by Jonathan Corbet)
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"During the stabilization phase of the kernel development cycle,
the -rc releases typically happen about once every week. 2.6.34-rc4
is a clear exception to that rule, coming nearly two weeks after
the preceding -rc3 release. The holdup in this case was a nasty
regression which occupied a number of kernel developers nearly full
time for days. The hunt for this bug is a classic story of what can
happen when the code gets too complex.
"Sending email to linux-kernel can be an intimidating prospect
for a number of reasons, one of which being that one never knows
when a massive thread - involving hundreds of messages copied back
to the original sender - might result. Borislav Petkov's 2.6.34-rc3
bug report was one such posting. In this case, though, the ensuing
thread was in no way inflammatory; it represents, instead, some of
the most intensive head-scratching which has been seen on the list
for a while.
"The bug, as reported by Borislav, was a null pointer
dereference which would happen reasonably reliably after
hibernating (and restarting) the system. It was quickly recognized
as being the same as another bug report filed the same day by
Steinar H. Gunderson, though this one did not involve hibernation.
The common thread was null pointer dereferences provoked by memory
pressure. The offending patch was identified by Linus almost
immediately; it's worth taking a look at what that patch did."