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Date: Mon, 09 Nov 2009 21:53:25 +0900 From: Kenji Kaneshige <kaneshige.kenji@...fujitsu.com> To: Peter Zijlstra <peterz@...radead.org> CC: mingo@...e.hu, linux-kernel@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au> Subject: Re: Kernel oops in resched_task() with 2.6.31.5 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. Thanks, Kenji Kaneshige -- 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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