linux-kernel - [PATCH v2] io_uring: fix refcounting with OOM

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Message-Id: <17022002efedf99758627055901c94d9fa344ec9.1579980745.git.asml.silence@gmail.com>
Date:   Sat, 25 Jan 2020 22:34:01 +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 v2] io_uring: fix refcounting with OOM

In case of out of memory the second argument of percpu_ref_put_many() in
io_submit_sqes() may evaluate into "nr - (-EAGAIN)", that is clearly
wrong.

Fixes: 2b85edfc0c90 ("io_uring: batch getting pcpu references")
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---

v2: rebase

 fs/io_uring.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 25f29ef81698..e79d6e47dc7b 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4896,8 +4896,11 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
 			break;
 	}
 
-	if (submitted != nr)
-		percpu_ref_put_many(&ctx->refs, nr - submitted);
+	if (unlikely(submitted != nr)) {
+		int ref_used = (submitted == -EAGAIN) ? 0 : submitted;
+
+		percpu_ref_put_many(&ctx->refs, nr - ref_used);
+	}
 	if (link)
 		io_queue_link_head(link);
 	if (statep)
-- 
2.24.0