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The case of the overly anonymous anon_vma

Apr 27, 2010, 06:03 (0 Talkback[s])
(Other stories by Jonathan Corbet)

"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."

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