linux-kernel - [PATCH 5.6 117/254] io_uring: fix ctx refcounting in io_submit

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Date:   Thu, 16 Apr 2020 15:23:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pavel Begunkov <asml.silence@...il.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.6 117/254] io_uring: fix ctx refcounting in io_submit_sqes()

From: Pavel Begunkov <asml.silence@...il.com>

commit 48bdd849e967f1c573d2b2bc24308e24a83f39c2 upstream.

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")
Cc: stable@...r.kernel.org # v5.6
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/io_uring.c |    1 -
 1 file changed, 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1242,7 +1242,6 @@ fallback:
 	req = io_get_fallback_req(ctx);
 	if (req)
 		goto got_it;
-	percpu_ref_put(&ctx->refs);
 	return NULL;
 }