Messages in this thread | | | Date | Mon, 16 Nov 2020 11:27:09 +0100 | From | Oleksandr Natalenko <> | Subject | Re: WARNING at kernel/sched/core.c:2013 migration_cpu_stop+0x2e3/0x330 |
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Hi.
On 16.11.2020 11:00, Valentin Schneider wrote: > On 15/11/20 22:32, Oleksandr Natalenko wrote: >> I'm running v5.10-rc3-rt7 for some time, and I came across this splat >> in >> dmesg: >> >> ``` >> [118769.951010] ------------[ cut here ]------------ >> [118769.951013] WARNING: CPU: 19 PID: 146 at kernel/sched/core.c:2013 > > Err, I didn't pick up on this back then, but isn't that check bogus? If > the > task is enqueued elsewhere, it's valid for it not to be affined > 'here'. Also that is_migration_disabled() check within is_cpu_allowed() > makes me think this isn't the best thing to call on a remote task. > > --- > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 1218f3ce1713..47d5b677585f 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2010,7 +2010,7 @@ static int migration_cpu_stop(void *data) > * valid again. Nothing to do. > */ > if (!pending) { > - WARN_ON_ONCE(!is_cpu_allowed(p, cpu_of(rq))); > + WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), p->cpus_ptr)); > goto out; > }
Not sure whether the check is legitimate, but FWIW I've managed to put a test task [1] (it spawns a lot of threads and applies affinity) into a permanent unkillable D state here:
``` [<0>] affine_move_task+0x2d3/0x620 [<0>] __set_cpus_allowed_ptr+0x164/0x210 [<0>] sched_setaffinity+0x21a/0x300 [<0>] __x64_sys_sched_setaffinity+0x8c/0xc0 [<0>] do_syscall_64+0x33/0x40 [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9 ```
I think this corresponds to something around here:
``` $ scripts/faddr2line kernel/sched/core.o affine_move_task+0x2d3 affine_move_task+0x2d3/0x620: arch_atomic_fetch_sub at /home/pf/linux-pf-edge/src/linux-5.10/./arch/x86/include/asm/atomic.h:190 (inlined by) atomic_fetch_sub_release at /home/pf/linux-pf-edge/src/linux-5.10/./include/asm-generic/atomic-instrumented.h:221 (inlined by) __refcount_sub_and_test at /home/pf/linux-pf-edge/src/linux-5.10/./include/linux/refcount.h:272 (inlined by) __refcount_dec_and_test at /home/pf/linux-pf-edge/src/linux-5.10/./include/linux/refcount.h:315 (inlined by) refcount_dec_and_test at /home/pf/linux-pf-edge/src/linux-5.10/./include/linux/refcount.h:333 (inlined by) affine_move_task at /home/pf/linux-pf-edge/src/linux-5.10/kernel/sched/core.c:2334 ```
or:
``` 2332 wait_for_completion(&pending->done); 2333 2334 if (refcount_dec_and_test(&pending->refs)) 2335 wake_up_var(&pending->refs); ```
I'm not positive about this being directly related to the original report, but I think it is still worth mentioning.
Thanks.
[1] https://gitlab.com/post-factum/burn_scheduler
-- Oleksandr Natalenko (post-factum)
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