This fixes couple of races which lead to infinite wait of park completion with the following backtraces:
[20801.303319] Call Trace: [20801.303321] ? __schedule+0x284/0x650 [20801.303323] schedule+0x33/0xc0 [20801.303324] schedule_timeout+0x1bc/0x210 [20801.303326] ? schedule+0x3d/0xc0 [20801.303327] ? schedule_timeout+0x1bc/0x210 [20801.303329] ? preempt_count_add+0x79/0xb0 [20801.303330] wait_for_completion+0xa5/0x120 [20801.303331] ? wake_up_q+0x70/0x70 [20801.303333] kthread_park+0x48/0x80 [20801.303335] io_finish_async+0x2c/0x70 [20801.303336] io_ring_ctx_wait_and_kill+0x95/0x180 [20801.303338] io_uring_release+0x1c/0x20 [20801.303339] __fput+0xad/0x210 [20801.303341] task_work_run+0x8f/0xb0 [20801.303342] exit_to_usermode_loop+0xa0/0xb0 [20801.303343] do_syscall_64+0xe0/0x100 [20801.303349] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [20801.303380] Call Trace: [20801.303383] ? __schedule+0x284/0x650 [20801.303384] schedule+0x33/0xc0 [20801.303386] io_sq_thread+0x38a/0x410 [20801.303388] ? __switch_to_asm+0x40/0x70 [20801.303390] ? wait_woken+0x80/0x80 [20801.303392] ? _raw_spin_lock_irqsave+0x17/0x40 [20801.303394] ? io_submit_sqes+0x120/0x120 [20801.303395] kthread+0x112/0x130 [20801.303396] ? kthread_create_on_node+0x60/0x60 [20801.303398] ret_from_fork+0x35/0x40 o kthread_park() waits for park completion, so io_sq_thread() loop should check kthread_should_park() along with khread_should_stop(), otherwise if kthread_park() is called before prepare_to_wait() the following schedule() never returns. o if the flag ctx->sqo_stop is observed by the io_sq_thread() loop it is quite possible, that kthread_should_park() check and the following kthread_parkme() is never called, because kthread_park() has not been yet called, but few moments later is is called and waits there for park completion, which never happens, because kthread has already exited. It seems that parking here is not needed at all (thread is parked and then stopped and never unparked), so here in this patch I simply rely on kthread_should_stop() check and then exit the thread. Signed-off-by: Roman Penyaev <[email protected]> Cc: Jens Axboe <[email protected]> Cc: [email protected] --- fs/io_uring.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 452e35357865..449c652bb334 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -231,7 +231,6 @@ struct io_ring_ctx { struct task_struct *sqo_thread; /* if using sq thread polling */ struct mm_struct *sqo_mm; wait_queue_head_t sqo_wait; - unsigned sqo_stop; struct { /* CQ ring */ @@ -2028,7 +2027,7 @@ static int io_sq_thread(void *data) set_fs(USER_DS); timeout = inflight = 0; - while (!kthread_should_stop() && !ctx->sqo_stop) { + while (!kthread_should_stop()) { bool all_fixed, mm_fault = false; int i; @@ -2140,9 +2139,6 @@ static int io_sq_thread(void *data) mmput(cur_mm); } - if (kthread_should_park()) - kthread_parkme(); - return 0; } @@ -2273,9 +2269,6 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx) static void io_sq_thread_stop(struct io_ring_ctx *ctx) { if (ctx->sqo_thread) { - ctx->sqo_stop = 1; - mb(); - kthread_park(ctx->sqo_thread); kthread_stop(ctx->sqo_thread); ctx->sqo_thread = NULL; } -- 2.21.0
