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io_uring: mitigate unlikely iopoll lag

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We have requests like IORING_OP_FILES_UPDATE that don't go through
->iopoll_list but get completed in place under ->uring_lock, and so
after dropping the lock io_iopoll_check() should expect that some CQEs
might have get completed in a meanwhile.

Currently such events won't be accounted in @nr_events, and the loop
will continue to poll even if there is enough of CQEs. It shouldn't be a
problem as it's not likely to happen and so, but not nice either. Just
return earlier in this case, it should be enough.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/66ef932cc66a34e3771bbae04b2953a8058e9d05.1625747741.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-07-08 13:37:06 +01:00 committed by Jens Axboe
parent c32aace0cf
commit 8f487ef2cb
1 changed files with 5 additions and 1 deletions
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6
fs/io_uring.c
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@ -2356,11 +2356,15 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
* very same mutex. * very same mutex.
*/ */
if (list_empty(&ctx->iopoll_list)) { if (list_empty(&ctx->iopoll_list)) {
u32 tail = ctx->cached_cq_tail;
mutex_unlock(&ctx->uring_lock); mutex_unlock(&ctx->uring_lock);
io_run_task_work(); io_run_task_work();
mutex_lock(&ctx->uring_lock); mutex_lock(&ctx->uring_lock);
if (list_empty(&ctx->iopoll_list)) /* some requests don't go through iopoll_list */
if (tail != ctx->cached_cq_tail ||
list_empty(&ctx->iopoll_list))
break; break;
} }
ret = io_do_iopoll(ctx, &nr_events, min); ret = io_do_iopoll(ctx, &nr_events, min);