[PATCH v2] watch_queue: Use local kmap in post_one_notification()

[PATCH v2] watch_queue: Use local kmap in post_one_notification()

[Davidlohr Bueso]

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@stgolabs.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

Re: [PATCH v2] watch_queue: Use local kmap in post_one_notification()

[Christian Brauner]

On Tue, 18 Nov 2025 13:07:06 -0800, Davidlohr Bueso wrote:
> 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].
> 
> [...]

Applied to the vfs-6.19.misc branch of the vfs/vfs.git tree.
Patches in the vfs-6.19.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.19.misc

[1/1] watch_queue: Use local kmap in post_one_notification()
      https://git.kernel.org/vfs/vfs/c/79cba9d67db3