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sched/fair: Don't NUMA balance for kthreads

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Stefano reported a crash with using SQPOLL with io_uring:

  BUG: kernel NULL pointer dereference, address: 00000000000003b0
  CPU: 2 PID: 1307 Comm: io_uring-sq Not tainted 5.7.0-rc7 #11
  RIP: 0010:task_numa_work+0x4f/0x2c0
  Call Trace:
   task_work_run+0x68/0xa0
   io_sq_thread+0x252/0x3d0
   kthread+0xf9/0x130
   ret_from_fork+0x35/0x40

which is task_numa_work() oopsing on current->mm being NULL.

The task work is queued by task_tick_numa(), which checks if current->mm is
NULL at the time of the call. But this state isn't necessarily persistent,
if the kthread is using use_mm() to temporarily adopt the mm of a task.

Change the task_tick_numa() check to exclude kernel threads in general,
as it doesn't make sense to attempt ot balance for kthreads anyway.

Reported-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/865de121-8190-5d30-ece5-3b097dc74431@kernel.dk
This commit is contained in:
Jens Axboe 2020-05-26 09:38:31 -06:00 committed by Ingo Molnar
parent 39f23ce07b
commit 18f855e574
1 changed files with 1 additions and 1 deletions
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kernel/sched/fair.c
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@ -2908,7 +2908,7 @@ 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->flags & (PF_EXITING | PF_KTHREAD)) || work->next != work)
return;
/*