fs/pipe: Use pipe_buf() helper to retrieve pipe buffer

Use pipe_buf() helper to retrieve the pipe buffer throughout the file
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/20250307052919.34542-4-kprateek.nayak@amd.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: kudureranganath

fs/pipe.c

@@ -274,7 +274,6 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
 		/* Read ->head with a barrier vs post_one_notification() */
 		unsigned int head = smp_load_acquire(&pipe->head);
 		unsigned int tail = pipe->tail;
-		unsigned int mask = pipe->ring_size - 1;
 
 #ifdef CONFIG_WATCH_QUEUE
 		if (pipe->note_loss) {
@@ -301,7 +300,7 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
 #endif
 
 		if (!pipe_empty(head, tail)) {
-			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+			struct pipe_buffer *buf = pipe_buf(pipe, tail);
 			size_t chars = buf->len;
 			size_t written;
 			int error;
@@ -471,8 +470,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 	was_empty = pipe_empty(head, pipe->tail);
 	chars = total_len & (PAGE_SIZE-1);
 	if (chars && !was_empty) {
-		unsigned int mask = pipe->ring_size - 1;
-		struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
+		struct pipe_buffer *buf = pipe_buf(pipe, head - 1);
 		int offset = buf->offset + buf->len;
 
 		if ((buf->flags & PIPE_BUF_FLAG_CAN_MERGE) &&
@@ -503,7 +501,6 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 
 		head = pipe->head;
 		if (!pipe_full(head, pipe->tail, pipe->max_usage)) {
-			unsigned int mask = pipe->ring_size - 1;
 			struct pipe_buffer *buf;
 			struct page *page = pipe->tmp_page;
 			int copied;
@@ -525,7 +522,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 			pipe->head = head + 1;
 
 			/* Insert it into the buffer array */
-			buf = &pipe->bufs[head & mask];
+			buf = pipe_buf(pipe, head);
 			buf->page = page;
 			buf->ops = &anon_pipe_buf_ops;
 			buf->offset = 0;