Messages in this thread | | | Date | Sat, 13 Sep 2014 17:03:14 +0800 | From | Daniel J Blueman <> | Subject | Re: [3.14] core onlining/hotplug regression |
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On 07/25/2014 05:05 PM, Thomas Gleixner wrote: > On Fri, 25 Jul 2014, Daniel J Blueman wrote: >> On a larger x86 system with 1728 cores, 3.15(.6) asserts on >> smpboot_thread_fn's td->cpu != smp_processor_id() consistently after ~1500 >> cores are online. >> >> Reverting the only directly related changes I could find [1,2] doesn't help. >> Debugging indicates there is a race where the created thread is quickly >> migrated to core 0 when this occurs, since smp_processor_id returns 0 in these >> cases. Thomas introduced a thread parked state to fix related issues a year >> back. Linux 3.14(.13) boots just nice. > > Weird. Commits [1,2] are definitely not the culprits. > >> Full boot output is at: >> https://resources.numascale.com/linux-315-thread-mig.txt > > Not really helpful, as we don't see what causes it. We just see the > wreckage. > >> Any theories so far? I'll start bisecting when I have full access to the >> system again in a week and I'll do some more debugging with intermittent >> access before then. > > One thing you could try is enabling tracing. > > "ftrace=function ftrace_dump_on_oops" > > It'll take a looooong time to spill out the traces, but that should > give us the root cause precisely.
It turns out that bisecting led to Lai's patch "Fix hotplug vs. set_cpus_allowed_ptr()" [1]. Reverting it prevents the smpboot.c BUG_ON(td->cpu != smp_processor_id()) in smpboot_thread_fn from tripping.
-- [1]
commit 6acbfb96976fc3350e30d964acb1dbbdf876d55e Author: Lai Jiangshan <laijs@cn.fujitsu.com> Date: Fri May 16 11:50:42 2014 +0800
sched: Fix hotplug vs. set_cpus_allowed_ptr()
Lai found that:
WARNING: CPU: 1 PID: 13 at arch/x86/kernel/smp.c:124 native_smp_send_reschedule+0x2d/0x4b() ... migration_cpu_stop+0x1d/0x22
was caused by set_cpus_allowed_ptr() assuming that cpu_active_mask is always a sub-set of cpu_online_mask.
This isn't true since 5fbd036b552f ("sched: Cleanup cpu_active madness").
So set active and online at the same time to avoid this particular problem.
Fixes: 5fbd036b552f ("sched: Cleanup cpu_active madness") Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michael wang <wangyun@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Cc: Toshi Kani <toshi.kani@hp.com> Link: http://lkml.kernel.org/r/53758B12.8060609@cn.fujitsu.com Signed-off-by: Ingo Molnar <mingo@kernel.org> -- Daniel J Blueman Principal Software Engineer, Numascale
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