linux-kernel - [PATCH v2] watch_queue: Use local kmap in post_one

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Message-Id: <20251118210706.1816303-1-dave@stgolabs.net>
Date: Tue, 18 Nov 2025 13:07:06 -0800
From: Davidlohr Bueso <dave@...olabs.net>
To: dhowells@...hat.com,
	brauner@...nel.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	dave@...olabs.net
Subject: [PATCH v2] watch_queue: Use local kmap in post_one_notification()

Replace the now deprecated kmap_atomic() with kmap_local_page().

Optimize for the non-highmem cases and avoid disabling preemption and
pagefaults, the caller's context is atomic anyway, but that is irrelevant
to kmap. The memcpy itself does not require any such semantics and the
mapping would hold valid across context switches anyway. Further, highmem
is planned to to be removed[1].

[1] https://lore.kernel.org/all/4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com/
Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
---
 kernel/watch_queue.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index 7e45559521af..52f89f1137da 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -119,9 +119,9 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE;
 	get_page(page);
 	len = n->info & WATCH_INFO_LENGTH;
-	p = kmap_atomic(page);
+	p = kmap_local_page(page);
 	memcpy(p + offset, n, len);
-	kunmap_atomic(p);
+	kunmap_local(p);
 
 	buf = pipe_buf(pipe, head);
 	buf->page = page;
-- 
2.39.5