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From: Jens Axboe <[email protected]>
To: Pavel Begunkov <[email protected]>,
	[email protected], [email protected]
Subject: Re: [PATCH 1/1] io_uring: don't wait when under-submitting
Date: Fri, 13 Dec 2019 11:22:46 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <5caa38be87f069eb4cc921d58ee1a98ff5d53978.1576223348.git.asml.silence@gmail.com>

On 12/13/19 12:51 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.

Why not just cap the wait_nr? If someone does to_submit = 8, wait_nr = 8,
and we only submit 4, just wait for 4? Ala:

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 81219a631a6d..4a76ccbb7856 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5272,6 +5272,10 @@ 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 <= 0)
+			goto done;
+		if (submitted != to_submit && min_complete > submitted)
+			min_complete = submitted;
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
 		unsigned nr_events = 0;
@@ -5284,7 +5288,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 			ret = io_cqring_wait(ctx, min_complete, sig, sigsz);
 		}
 	}
-
+done:
 	percpu_ref_put(&ctx->refs);
 out_fput:
 	fdput(f);

-- 
Jens Axboe


  reply	other threads:[~2019-12-13 20:40 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-13  7:51 [PATCH 1/1] io_uring: don't wait when under-submitting Pavel Begunkov
2019-12-13 18:22 ` Jens Axboe [this message]
2019-12-13 18:32   ` Jens Axboe
2019-12-13 21:32     ` Pavel Begunkov
2019-12-13 21:48       ` Jens Axboe
2019-12-14 14:31 ` [PATCH v2] " Pavel Begunkov
2019-12-14 14:39   ` Jens Axboe
2019-12-14 14:44     ` Pavel Begunkov
2019-12-14 14:53   ` [PATCH v3] " Pavel Begunkov
2019-12-14 18:43     ` Jens Axboe
2019-12-15  5:42       ` Jens Axboe
2019-12-15 15:48         ` Pavel Begunkov
2019-12-15 21:33           ` Jens Axboe
2019-12-16 16:31             ` [PATCH v4] " Pavel Begunkov
2019-12-16 16:47             ` [PATCH v3] " Pavel Begunkov
2019-12-16 16:51               ` Jens Axboe

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