linux-kernel - [PATCH 1/2] pipe: remove pipe_full check with wrong head in pipe

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Date:   Sun,  8 Oct 2023 17:48:00 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     viro@...iv.linux.org.uk, brauner@...nel.org, dhowells@...hat.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] pipe: remove pipe_full check with wrong head in pipe_write

In pipe_write we have:
	head = pipe->head;
	if (!pipe_full(head, pipe->tail, pipe->max_usage))
		pipe->head = head + 1;
		/* write data to buffer at head */

	/* supposed to check if pipe is full after write */
	if (!pipe_full(head, pipe->tail, pipe->max_usage))
		continue

The second pipe_full expects head after write but head before write is
used. Luckily, we will call pipe_full with correct reloaded pipe->head
in new loop cycle and stop writing correctly. Remove wrong pipe_full
check and simply continue to first pipe_full check after write done to
avoid unnecessary check.

Fixes: a194dfe6e6f6 ("pipe: Rearrange sequence in pipe_write() to preallocate slot")
Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
---
 fs/pipe.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 2d88f73f585a..b19875720ff1 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -542,10 +542,9 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 
 			if (!iov_iter_count(from))
 				break;
-		}
 
-		if (!pipe_full(head, pipe->tail, pipe->max_usage))
 			continue;
+		}
 
 		/* Wait for buffer space to become available. */
 		if ((filp->f_flags & O_NONBLOCK) ||
-- 
2.30.0