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(%d %s) flags=%lx\n", p->pid, p->comm, p->flags); > > log from dual socket AMD Milanx 7573X server: > > [74615.841401] # entries-in-buffer/entries-written: 1/1 #P:128 > [74615.841401] # > [74615.841401] # _-----=> irqs-off/BH-disabled > [74615.841401] # / _----=> need-resched > [74615.841401] # | / _---=> hardirq/softirq > [74615.841401] # || / _--=> preempt-depth > [74615.841401] # ||| / _-=> migrate-disable > [74615.841401] # |||| / delay > [74615.841401] # TASK-PID CPU# ||||| TIMESTAMP FUNCTION > [74615.841401] # | | | ||||| | | > [74615.841401] migration/6-54 [006] d..5. 58590.368364: > __migrate_swap_task: !! (2939199 stress-ng-sem) flags=40004c > > debug code caught a task with p->mm == NULL during __migrate_swap_task(). > > Trace shows: > * It was a stress-ng-sem process (PID 2939199), > * That process was in the process of exiting (PF_EXITING | PF_EXITPIDONE), Thanks Jirka. So this race condition is related to task exit. > * And was a workqueue worker (PF_WQ_WORKER), > * It explains why p->mm had already been freed > > I'm curious as to why the command is stress-ng-sem, and the flag > indicates it is a workqueue worker. The flag 0x40004c is PF_EXITING PF_POSTCOREDUMP PF_FORKNOEXEC PF_RANDOMIZE according to latest https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/sched.h?h=v6.16-rc4 thanks, Chenyu> > More jobs are still running. I will keep an eye on them and report the > other cases as they finish. > > Jirka > > On Tue, Jul 1, 2025 at 5:10 PM Jirka Hladky wrote: >> >> Hi Chenyu and Libo, >> >> I agree, let's wait for the results. Hopefully, we can fix the root >> cause based on the debug messages. >> >> There was a problem with the infrastructure over the weekend, so I had >> to restart the jobs yesterday. I should have results tomorrow. >> >> Stay tuned. >> Jirka >> >> >> On Tue, Jul 1, 2025 at 4:59 PM Chen, Yu C wrote: >>> >>> Hi Libo, >>> >>> On 7/1/2025 3:32 PM, Libo Chen wrote: >>>> Hi Chenyu, >>>> >>>> On 6/27/25 00:33, Chen, Yu C wrote: >>>>> On 6/27/2025 3:16 PM, Chen, Yu C wrote: >>>>>> Hi Jirka, >>>>>> >>>>>> On 6/27/2025 5:46 AM, Jirka Hladky wrote: >>>>>>> Hi Chen and all, >>>>>>> >>>>>>> we have now verified that the following commit causes a kernel panic >>>>>>> discussed in this thread: >>>>>>> >>>>>>> ad6b26b6a0a79 sched/numa: add statistics of numa balance task >>>>>>> >>>>>>> Reverting this commit fixes the issue. >>>>>>> >>>>>>> I'm happy to help debug this further or test a proposed fix. >>>>>>> >>>>>> >>>>>> Thanks very much for your report, it seems that there is a >>>>>> race condition that when the swap task candidate was chosen, >>>>>> but its mm_struct get released due to task exit, then later >>>>>> when doing the task swaping, the p->mm is NULL which caused >>>>>> the problem: >>>>>> >>>>>> CPU0 CPU1 >>>>>> : >>>>>> ... >>>>>> task_numa_migrate >>>>>> task_numa_find_cpu >>>>>> task_numa_compare >>>>>> # a normal task p is chosen >>>>>> env->best_task = p >>>>>> >>>>>> # p exit: >>>>>> exit_signals(p); >>>>>> p->flags |= PF_EXITING >>>>>> exit_mm >>>>>> p->mm = NULL; >>>>>> >>>>>> migrate_swap_stop >>>>>> __migrate_swap_task((arg->src_task, arg->dst_cpu) >>>>>> count_memcg_event_mm(p->mm, NUMA_TASK_SWAP)# p->mm is NULL >>>>>> >>>>>> Could you please help check if the following debug patch works, >>>>> >>>>> Attached the patch: >>>>> >>>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >>>>> index 8988d38d46a3..82fc966b390c 100644 >>>>> --- a/kernel/sched/core.c >>>>> +++ b/kernel/sched/core.c >>>>> @@ -3364,7 +3364,12 @@ static void __migrate_swap_task(struct task_struct *p, int cpu) >>>>> { >>>>> __schedstat_inc(p->stats.numa_task_swapped); >>>>> count_vm_numa_event(NUMA_TASK_SWAP); >>>>> - count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); >>>>> + if (unlikely(!p->mm)) { >>>> >>>> I am starting to wonder if we should keep this check and add a big fat warning >>>> like "there is a bug here, please report it!" rather than brick the kernel. >>>> A kernel panic, for sure, helps catch bugs like this more than a line of dmesg, >>>> so it's a tradeoff I guess. What do you think? >>>> >>> >>> I agree with you that adding something like WARN_ON_ONCE() >>> could help, and it seems that the kernel panic is not expected >>> in this scenario because this feature is a statistic calculation >>> rather than the critical logic. Maybe waiting for Jirka's feedback >>> to decide the next step. >>> >>> thanks, >>> Chenyu >>> >>> >>> >>>> >>>> Thanks, >>>> Libo >>>> >>>>> + trace_printk("!! (%d %s) flags=%lx\n", p->pid, p->comm, >>>>> + p->flags); >>>>> + } else { >>>>> + count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); >>>>> + } >>>>> >>>>> if (task_on_rq_queued(p)) { >>>>> struct rq *src_rq, *dst_rq; >>>> >>> >> >> >> -- >> -Jirka > > >