[PATCH 4.4 008/101] sched/fair: Dont NUMA balance for kthreads

Greg Kroah-Hartman
2020-06-19T16:54:35Z

From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit 18f855e574d9799a0e7489f8ae6fd8447d0dd74a ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/sched/fair.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0daf4a40a985..971e31e47bfd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2325,7 +2325,7 @@ 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;

/*
--
2.25.1