From: Pavel Begunkov <asml.silence@gmail.com>
Date: Wed, 18 Dec 2019 16:53:45 +0000 (+0300)
Subject: io_uring: don't wait when under-submitting
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=7c504e65206a4379ff38fe41d21b32b6c2c3e53e;p=openwrt%2Fstaging%2Fblogic.git

io_uring: don't wait when under-submitting

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>
---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1d4e7332ccae..81e7fe6dee18 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5135,6 +5135,9 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 		submitted = io_submit_sqes(ctx, to_submit, f.file, fd,
 					   &cur_mm, false);
 		mutex_unlock(&ctx->uring_lock);
+
+		if (submitted != to_submit)
+			goto out;
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
 		unsigned nr_events = 0;
@@ -5148,6 +5151,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 		}
 	}
 
+out:
 	percpu_ref_put(&ctx->refs);
 out_fput:
 	fdput(f);