[PATCH 5.4 108/165] io_uring: dont wait when under-submitting

Greg Kroah-Hartman
2020-01-11T10:30:20Z

From: Pavel Begunkov <asml.silence@gmail.com>

[ Upstream commit 7c504e65206a4379ff38fe41d21b32b6c2c3e53e ]

There is no reliable way to submit and wait in a single syscall, as
io_submit_sqes() may under-consume sqes (in case of an early error).
Then it will wait for not-yet-submitted requests, deadlocking the user
in most cases.

Don't wait/poll if can't submit all sqes

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/io_uring.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a60c6315a348..709671faaed6 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3721,6 +3721,9 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
mutex_lock(&ctx->uring_lock);
submitted = io_ring_submit(ctx, to_submit);
mutex_unlock(&ctx->uring_lock);
+
+ if (submitted != to_submit)
+ goto out;
}
if (flags & IORING_ENTER_GETEVENTS) {
unsigned nr_events = 0;
@@ -3734,6 +3737,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
}
}

+out:
percpu_ref_put(&ctx->refs);
out_fput:
fdput(f);
--
2.20.1