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Date: Tue, 10 Nov 2009 06:15:37 +0100 From: Ingo Molnar <mingo@...e.hu> To: Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>, stable kernel team <stable@...nel.org> Cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au> Subject: Re: Kernel oops in resched_task() with 2.6.31.5 * Kenji Kaneshige <kaneshige.kenji@...fujitsu.com> wrote: > Kenji Kaneshige wrote: > >Peter Zijlstra wrote: > >>On Mon, 2009-11-09 at 21:31 +0900, Kenji Kaneshige wrote: > >>>Hi, > >>> > >>>I frequently encounter the kernel oops attached below in resched_task() > >>>with 2.6.31.5. This kernel oops happens also with 2.6.32-rc5. I don't > >>>know about other kernel. > >>> > >>>Here is my analysis: > >>> > >>>The immediate cause of this kernel oops is that NULL was passed to > >>>resched_task() from resched_cpu(). From my investigation, this was > >>>caused as follows: > >>> > >>>- trigger_load_balance() caluculated cpu number of idle load balancer > >>> using find_new_ilb(), and find_new_ilb() returned *offline* CPU > >>> number (16 in my case). Note that I didn't do any CPU hotplug > >>> operation. On my system, present, online and offline under > >>> /sys/devices/system/cpu/ are > >>> > >>> [kanesige@...alhost ~]$ cat /sys/devices/system/cpu/present > >>> 0-15 > >>> [kanesige@...alhost ~]$ cat /sys/devices/system/cpu/online > >>> 0-15 > >>> [kanesige@...alhost ~]$ cat /sys/devices/system/cpu/offline > >>> 16-255 > >>> > >>> And nr_cpu_ids is 256. > >>> > >>>- resched_cpu() calculated current task by cpu_curr() with offline CPU > >>> number. > >>> > >>>So this kernel oops seems to be caused by invalid CPU number returned > >>>from find_new_ilb(). I don't know the find_new_ilb() implementation, > >>>but I suspect the initialization of cpumasks used by find_new_ilb(). > >>>The patch attached below seems to fix the problem (With this patch, > >>>the kernel oops doesn't happen). But I don't know if this is the > >>>correct fix. > >> > >>Please send patches against -tip. > >> > >>You might find that Rusty has already fixed a similar issue there in > >>commit: 49557e620339cb134127b5bfbcfecc06b77d0232. > >> > >>Now, Rusty's patch does not clear the ilb mask, so maybe it doesn't > >>fully cover your issue, please test. > >> > > > >Thank you for quick response. > > > >I didn't notice Rusty's fix. > >I'll look at and test it tomorrow. > > > > I tested Rusty's patch and confirmed it fixes the problem. Thanks. -stable team, please cherry-pick this upstream commit for .31.x: 49557e6: sched: Fix boot crash by zalloc()ing most of the cpu masks Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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