Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
To:     David Howells <dhowells@redhat.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
From:   Jens Axboe <axboe@kernel.dk>
Subject: [PATCH]: splice fix opipe_prep() full check
Message-ID: <cf341c51-ba8c-4f81-fe4e-6bf8190293e3@kernel.dk>
Date:   Wed, 20 May 2020 18:42:56 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The patch converting pipes to head and tail pointers mistakenly
turned the splice pipe-to-pipe opipe check into something
nonsensical. It's supposed to check if we have room in the pipe,
and return success if we do. If not, wait for room in the pipe.
Instead it's now returning success for a full pipe, and entering
the slow path for a non-full pipe.

Cc: stable@vger.kernel.org
Fixes: 8cefc107ca54 ("pipe: Use head and tail pointers for the ring, not cursor and length")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

I didn't check if the offending commit had other logical fumbles.

diff --git a/fs/splice.c b/fs/splice.c
index fd0a1e7e5959..4e53efbd621d 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1494,7 +1494,7 @@ static int opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
 	 * Check pipe occupancy without the inode lock first. This function
 	 * is speculative anyways, so missing one is ok.
 	 */
-	if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
+	if (!pipe_full(pipe->head, pipe->tail, pipe->max_usage))
 		return 0;
 
 	ret = 0;

-- 
Jens Axboe