[PATCH v5] io_uring: don't wait when under-submitting

[PATCH v5] io_uring: don't wait when under-submitting

[Pavel Begunkov]

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>
---

v5: as the v1, but doesn't return -EAGAIN

 fs/io_uring.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index fd85f9d3a8e1..eca025f38614 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5133,6 +5133,9 @@ 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;
@@ -5146,6 +5149,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 		}
 	}
 
+out:
 	percpu_ref_put(&ctx->refs);
 out_fput:
 	fdput(f);
-- 
2.24.0

Re: [PATCH v5] io_uring: don't wait when under-submitting

[Jens Axboe]

On 12/18/19 9:53 AM, Pavel Begunkov wrote:
> 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

This looks great, thanks, applied.

-- 
Jens Axboe