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 <[email protected]>
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 <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Gautham R. Shenoy <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Michael wang <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Srivatsa S. Bhat <[email protected]>
Cc: Toshi Kani <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
--
Daniel J Blueman
Principal Software Engineer, Numascale
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