linux-kernel - [PATCH] fs/pipe.c: simplify tmp

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Message-ID: <20250307221004.1115255-1-linux@rasmusvillemoes.dk>
Date: Fri,  7 Mar 2025 23:10:04 +0100
From: Rasmus Villemoes <linux@...musvillemoes.dk>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: David Howells <dhowells@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] fs/pipe.c: simplify tmp_page handling

Assigning the newly allocated page to pipe->tmp_page, only to
unconditionally clear ->tmp_page a little later, seems somewhat odd.

It made sense prior to commit a194dfe6e6f6 ("pipe: Rearrange sequence
in pipe_write() to preallocate slot"), when a user copy was done
between the allocation and the buf->page = page assignment, and a
failure there would then just leave the pipe's one-element page cache
populated. Now, the same purpose is served by the page being inserted
as a size-0 buffer, and the next write attempting to merge with that
buffer.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 fs/pipe.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 4d0799e4e719..097400cce241 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -508,13 +508,14 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 			struct page *page = pipe->tmp_page;
 			int copied;
 
-			if (!page) {
+			if (page) {
+				pipe->tmp_page = NULL;
+			} else {
 				page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);
 				if (unlikely(!page)) {
 					ret = ret ? : -ENOMEM;
 					break;
 				}
-				pipe->tmp_page = page;
 			}
 
 			/* Allocate a slot in the ring in advance and attach an
@@ -534,7 +535,6 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 				buf->flags = PIPE_BUF_FLAG_PACKET;
 			else
 				buf->flags = PIPE_BUF_FLAG_CAN_MERGE;
-			pipe->tmp_page = NULL;
 
 			copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
 			if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
-- 
2.48.1