Messages in this thread | | | Date | Thu, 18 Oct 2012 14:50:54 -0600 | Subject | Re: [tip:sched/core] sched: Fix race in task_group() | From | cwillu <> |
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On Thu, Oct 18, 2012 at 7:33 AM, Luis Henriques <luis.henriques@canonical.com> wrote: > On Thu, Oct 18, 2012 at 12:23:38PM +0200, Stefan Bader wrote: >> On 18.10.2012 10:27, cwillu wrote: >> > On Tue, Jul 24, 2012 at 8:21 AM, tip-bot for Peter Zijlstra >> > <peterz@infradead.org> wrote: >> >> Commit-ID: 8323f26ce3425460769605a6aece7a174edaa7d1 >> >> Gitweb: http://git.kernel.org/tip/8323f26ce3425460769605a6aece7a174edaa7d1 >> >> Author: Peter Zijlstra <peterz@infradead.org> >> >> AuthorDate: Fri, 22 Jun 2012 13:36:05 +0200 >> >> Committer: Ingo Molnar <mingo@kernel.org> >> >> CommitDate: Tue, 24 Jul 2012 13:58:20 +0200 >> >> >> >> sched: Fix race in task_group() >> >> >> >> Stefan reported a crash on a kernel before a3e5d1091c1 ("sched: >> >> Don't call task_group() too many times in set_task_rq()"), he >> >> found the reason to be that the multiple task_group() >> >> invocations in set_task_rq() returned different values. >> >> >> >> Looking at all that I found a lack of serialization and plain >> >> wrong comments. >> >> >> >> The below tries to fix it using an extra pointer which is >> >> updated under the appropriate scheduler locks. Its not pretty, >> >> but I can't really see another way given how all the cgroup >> >> stuff works. >> >> >> >> Reported-and-tested-by: Stefan Bader <stefan.bader@canonical.com> >> >> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> >> >> Link: http://lkml.kernel.org/r/1340364965.18025.71.camel@twins >> >> Signed-off-by: Ingo Molnar <mingo@kernel.org> >> > >> > I just finished bisecting a crash on boot to this commit; booting with >> > "noautogroup" brings it back. >> > >> > 3.5.4 is the latest -stable that still boots, and none of the 3.6 rc's >> > boot at all. >> > >> > Photo of the bug (3.6.0next is 3.6 + btrfs's for-linus): >> > https://lh5.googleusercontent.com/-0DY-YYhgvzs/UHdB-BQdzMI/AAAAAAAAAEg/QhY9rgxnv98/s811/2012-10-11 >> > >> >> On a very quick glance I wonder whether there might be a case where sched_fork >> goes into set_task_cpu with a different cpu than the current but has not yet >> task_group.sched_task_group set to something valid... >> >> > > I was looking at another bug report [1] which may be related with this > issue. Basically, it looks like there is a race window where > resetting sched_autogroup_enabled will cause a crash on > shutdown/reboot. In the bug report, the user has added: > > echo 0 > /proc/sys/kernel/sched_autogroup_enabled > > to /etc/rc.local. This will cause a NULL pointer dereference during > shutdown (and it is reproducible with mainline kernel 3.7.0-rc1). > > By using the kernel parameter noautogroup I *wasn't* able to reproduce > this issue.
Ah, yes, that makes sense. I just checked, and the machine has "kernel.sched_autogroup_enabled = 0" in /etc/sysctl.conf, which would have the same effect.
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