Messages in this thread | | | Date | Mon, 10 Aug 2009 18:10:07 +0200 | From | Pavel Machek <> | Subject | Re: [BUG] race of RCU vs NOHU |
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Hi!
> > > I analysed a dump of a hanging 2.6.30 system and found what I think is > > > a bug of RCU vs NOHZ. There are a number of patches ontop of that > > > kernel but they should be independent of the bug. > > > > > > The systems has 4 cpus and uses classic RCU. cpus #0, #2 and #3 woke up > > > recently, cpu #1 has been sleeping for 5 minutes, but there is a pending > > > rcu batch. The timer wheel for cpu #1 is empty, it will continue to > > > sleep for NEXT_TIMER_MAX_DELTA ticks. > > > > Congratulations, Martin! You have exercised what to date has been a > > theoretical bug identified last year by Manfred Spraul. The fix is to > > switch from CONFIG_RCU_CLASSIC to CONFIG_RCU_TREE, which was added in > > 2.6.29. > > > > Of course, if you need to work with an old kernel version, you might > > still need a patch, perhaps for the various -stable versions. If so, > > please let me know -- otherwise, I will focus forward on CONFIG_RCU_TREE > > rather than backwards on CONFIG_RCU_CLASSIC. > > SLES11 is 2.6.27 and uses classic RCU. The not-so theoretical bug is > present there and I think it needs to be fixed :-/
Plus... if config_rcu_classic is known buggy (and you are not willing to fix it), it should be disabled (or made depend on !CONFIG_NOHZ, or maybe made depend on CONFIG_BROKEN).
Ugh. rcu_classic does not seem to have help text, and I'm running known bad code here :-(.
Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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