linux-kernel - [PATCH] io_uring: fix ctx refcounting in io_submit

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Message-Id: <8b53ce4539784423b493fdbfae9bd4c720b24d2a.1586120916.git.asml.silence@gmail.com>
Date:   Mon,  6 Apr 2020 00:08:52 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] io_uring: fix ctx refcounting in io_submit_sqes()

If io_get_req() fails, it drops a ref. Then, awhile keeping @submitted
unmodified, io_submit_sqes() breaks the loop and puts @nr - @submitted
refs. For each submitted req a ref is dropped in io_put_req() and
friends. So, for @nr taken refs there will be
(@nr - @submitted + @submitted + 1) dropped.

Remove ctx refcounting from io_get_req(), that at the same time makes
it clearer.

Fixes: 2b85edfc0c90 ("io_uring: batch getting pcpu references")
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 fs/io_uring.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 78ae8e8ed5bf..79bd22289d73 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1342,7 +1342,6 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
 	req = io_get_fallback_req(ctx);
 	if (req)
 		goto got_it;
-	percpu_ref_put(&ctx->refs);
 	return NULL;
 }

-- 
2.24.0