On 5/25/20 1:21 PM, Peter Zijlstra wrote: > On Mon, May 25, 2020 at 08:10:27AM -0600, Jens Axboe wrote: >> I think the odd part here is that task_tick_numa() checks for a >> valid mm, and queues work if the task has it. But for the sqpoll >> kthread, the mm can come and go. By the time the task work is run, >> the mm is gone and we oops on current->mm == NULL. >> >> I think the below should fix it: >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 538ba5d94e99..24a8557f001f 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -2908,7 +2908,8 @@ static void task_tick_numa(struct rq *rq, struct >> task_struct *curr) >> /* >> * We don't care about NUMA placement if we don't have memory. >> */ >> - if (!curr->mm || (curr->flags & PF_EXITING) || work->next != work) >> + if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) || >> + work->next != work) >> return; > > Ah, I think that's one more instance of '!p->mm' != is_kthread(). A > while ago someone went and cleaned a bunch of them up. Clearly this one > was missed. > > I'm thinking just: > > if ((curr->flags & (PF_EXITING | PF_KTHREAD)) || work->next != work) > > should be enough.
Yeah it should, no point in checking both ->mm == NULL and PF_KTHREAD. -- Jens Axboe
