linux-kernel - [PATCH 1/1] io_uring: fix refcounting with OOM

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Message-Id: <fa69cae513308ef3f681e13888a4f551c67ef3a2.1579942715.git.asml.silence@gmail.com>
Date:   Sat, 25 Jan 2020 11:59:30 +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 1/1] 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>
---
 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 a4b496815783..744e8a90b543 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4912,8 +4912,11 @@ 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);
+	}
 
 	io_submit_end(ctx);
 	if (nr > IO_PLUG_THRESHOLD)
-- 
2.24.0