linux-kernel - [PATCH 3/4] fs/pipe: remove unnecessary spinlock from pipe

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Date:   Thu, 21 Sep 2023 09:57:54 +0200
From:   Max Kellermann <max.kellermann@...os.com>
To:     viro@...iv.linux.org.uk, brauner@...nel.org, howells@...hat.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Max Kellermann <max.kellermann@...os.com>
Subject: [PATCH 3/4] fs/pipe: remove unnecessary spinlock from pipe_write()

This reverts commit 8df441294dd3 ("pipe: Check for ring full inside of
the spinlock in pipe_write()") which was obsoleted by commit
c73be61cede ("pipe: Add general notification queue support") because
now pipe_write() fails early with -EXDEV if there is a watch_queue.

Without a watch_queue, no notifications can be posted to the pipe and
mutex protection is enough, as can be seen in splice_pipe_to_pipe()
which does not use the spinlock either.

Signed-off-by: Max Kellermann <max.kellermann@...os.com>
---
 fs/pipe.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 6ecaccb48738..939def02c18c 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -505,16 +505,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 			 * it, either the reader will consume it or it'll still
 			 * be there for the next write.
 			 */
-			spin_lock_irq(&pipe->rd_wait.lock);
-
-			head = pipe->head;
-			if (pipe_full(head, pipe->tail, pipe->max_usage)) {
-				spin_unlock_irq(&pipe->rd_wait.lock);
-				continue;
-			}
-
 			pipe->head = head + 1;
-			spin_unlock_irq(&pipe->rd_wait.lock);
 
 			/* Insert it into the buffer array */
 			buf = &pipe->bufs[head & mask];
-- 
2.39.2