[PATCH 6.12.y 1/2] kernel/watch_queue: Use pipe_buf() to retrieve the pipe buffer

[Sasha Levin <sashal@kernel.org>]

From: K Prateek Nayak <kprateek.nayak@amd.com>

[ Upstream commit 547476063e123e73fc3aea8432104ab092ffea84 ]

Use pipe_buf() helper to retrieve the pipe buffer in
post_one_notification() replacing the open-coded the logic.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20250307052919.34542-3-kprateek.nayak@amd.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Stable-dep-of: 5e531d62f1f8 ("watch_queue: Fix note pool publication race in watch_queue_set_size()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/watch_queue.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index 6d1936fb8ff02..5da67a1047d00 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -101,12 +101,11 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	struct pipe_inode_info *pipe = wqueue->pipe;
 	struct pipe_buffer *buf;
 	struct page *page;
-	unsigned int head, tail, mask, note, offset, len;
+	unsigned int head, tail, note, offset, len;
 	bool done = false;
 
 	spin_lock_irq(&pipe->rd_wait.lock);
 
-	mask = pipe->ring_size - 1;
 	head = pipe->head;
 	tail = pipe->tail;
 	if (pipe_full(head, tail, pipe->ring_size))
@@ -124,7 +123,7 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	memcpy(p + offset, n, len);
 	kunmap_atomic(p);
 
-	buf = &pipe->bufs[head & mask];
+	buf = pipe_buf(pipe, head);
 	buf->page = page;
 	buf->private = (unsigned long)wqueue;
 	buf->ops = &watch_queue_pipe_buf_ops;
@@ -147,7 +146,7 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	return done;
 
 lost:
-	buf = &pipe->bufs[(head - 1) & mask];
+	buf = pipe_buf(pipe, head - 1);
 	buf->flags |= PIPE_BUF_FLAG_LOSS;
 	goto out;
 }
-- 
2.53.0