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io_uring: add need_resched() check in inner poll loop 

The outer poll loop checks for whether we need to reschedule, and
returns to userspace if we do. However, it's possible to get stuck
in the inner loop as well, if the CPU we are running on needs to
reschedule to finish the IO work.

Add the need_resched() check in the inner loop as well. This fixes
a potential hang if the kernel is configured with
CONFIG_PREEMPT_VOLUNTARY=y.

Reported-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Tested-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2019-08-21 22:19:11 -06:00
parent 7035eef449
commit 08f5439f1d
1 changed files with 7 additions and 1 deletions
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8
fs/io_uring.c
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@ -778,7 +778,7 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
static int io_iopoll_getevents(struct io_ring_ctx *ctx, unsigned int *nr_events,
long min)
{
while (!list_empty(&ctx->poll_list)) {
while (!list_empty(&ctx->poll_list) && !need_resched()) {
int ret;
ret = io_do_iopoll(ctx, nr_events, min);
@ -805,6 +805,12 @@ static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
unsigned int nr_events = 0;
io_iopoll_getevents(ctx, &nr_events, 1);
/*
* Ensure we allow local-to-the-cpu processing to take place,
* in this case we need to ensure that we reap all events.
*/
cond_resched();
}
mutex_unlock(&ctx->uring_lock);
}