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io_uring: don't wait when under-submitting

PATCH In review Pavel Begunkov 2 participants 2 messages Dec 18, 2019 1 message not in the archive

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A message that is not in the archive (sent off-list or not yet received): [email protected]

Pavel Begunkov

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#1 lore raw

PATCH v5 1/1 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 <[email protected]>

---

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

 fs/io_uring.c | 4 ++++
 1 file changed, 4 insertions(+)
fs/io_uring.c +4 -0
index fd85f9d3a8e1..eca025f38614 100644
@@ -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);
Signature · 1 line
2.24.0
maintainer
#2 lore raw
Quoted 6 lines · 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

This looks great, thanks, applied.

Signature · 1 line
Jens Axboe