From 8f487ef2cbb2d4f6ca8c113d70da63baaf68c91a Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Thu, 8 Jul 2021 13:37:06 +0100 Subject: io_uring: mitigate unlikely iopoll lag 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 Link: https://lore.kernel.org/r/66ef932cc66a34e3771bbae04b2953a8058e9d05.1625747741.git.asml.silence@gmail.com Signed-off-by: Jens Axboe --- fs/io_uring.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 8f2a66903f5a..7167c61c6d1b 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -2356,11 +2356,15 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min) * very same mutex. */ if (list_empty(&ctx->iopoll_list)) { + u32 tail = ctx->cached_cq_tail; + mutex_unlock(&ctx->uring_lock); io_run_task_work(); 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; } ret = io_do_iopoll(ctx, &nr_events, min); -- cgit v1.2.3