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io_uring: fix __io_iopoll_check deadlock in io_sq_thread 

Since commit a3a0e43fd7 ("io_uring: don't enter poll loop if we have
CQEs pending"), if we already events pending, we won't enter poll loop.
In case SETUP_IOPOLL and SETUP_SQPOLL are both enabled, if app has
been terminated and don't reap pending events which are already in cq
ring, and there are some reqs in poll_list, io_sq_thread will enter
__io_iopoll_check(), and find pending events, then return, this loop
will never have a chance to exit.

I have seen this issue in fio stress tests, to fix this issue, let
io_sq_thread call io_iopoll_getevents() with argument 'min' being zero,
and remove __io_iopoll_check().

Fixes: a3a0e43fd7 ("io_uring: don't enter poll loop if we have CQEs pending")
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Xiaoguang Wang 2020-02-22 14:46:05 +08:00 committed by Jens Axboe
parent 7143b5ac57
commit c7849be9cc
1 changed files with 9 additions and 18 deletions
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27
fs/io_uring.c
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@ -1672,11 +1672,17 @@ static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
mutex_unlock(&ctx->uring_lock);
}
static int __io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
long min)
static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
long min)
{
int iters = 0, ret = 0;
/*
* We disallow the app entering submit/complete with polling, but we
* still need to lock the ring to prevent racing with polled issue
* that got punted to a workqueue.
*/
mutex_lock(&ctx->uring_lock);
do {
int tmin = 0;
@ -1712,21 +1718,6 @@ static int __io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
ret = 0;
} while (min && !*nr_events && !need_resched());
return ret;
}
static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
long min)
{
int ret;
/*
* We disallow the app entering submit/complete with polling, but we
* still need to lock the ring to prevent racing with polled issue
* that got punted to a workqueue.
*/
mutex_lock(&ctx->uring_lock);
ret = __io_iopoll_check(ctx, nr_events, min);
mutex_unlock(&ctx->uring_lock);
return ret;
}
@ -5118,7 +5109,7 @@ static int io_sq_thread(void *data)
*/
mutex_lock(&ctx->uring_lock);
if (!list_empty(&ctx->poll_list))
__io_iopoll_check(ctx, &nr_events, 0);
io_iopoll_getevents(ctx, &nr_events, 0);
else
inflight = 0;
mutex_unlock(&ctx->uring_lock);