This is a note to let you know that I've just added the patch titled
mm/rmap: fix misplaced parenthesis of a likely()
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-rmap-fix-misplaced-parenthesis-of-a-likely.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f67f8d4a8c1e1ebc85a6cbdb9a7266f14863461c Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
Date: Fri, 1 Dec 2023 14:59:36 -0500
Subject: mm/rmap: fix misplaced parenthesis of a likely()
From: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
commit f67f8d4a8c1e1ebc85a6cbdb9a7266f14863461c upstream.
Running my yearly branch profiler to see where likely/unlikely annotation
may be added or removed, I discovered this:
correct incorrect % Function File Line
------- --------- - -------- ---- ----
0 457918 100 page_try_dup_anon_rmap rmap.h 264
[..]
458021 0 0 page_try_dup_anon_rmap rmap.h 265
I thought it was interesting that line 264 of rmap.h had a 100% incorrect
annotation, but the line directly below it was 100% correct. Looking at the
code:
if (likely(!is_device_private_page(page) &&
unlikely(page_needs_cow_for_dma(vma, page))))
It didn't make sense. The "likely()" was around the entire if statement
(not just the "!is_device_private_page(page)"), which also included the
"unlikely()" portion of that if condition.
If the unlikely portion is unlikely to be true, that would make the entire
if condition unlikely to be true, so it made no sense at all to say the
entire if condition is true.
What is more likely to be likely is just the first part of the if statement
before the && operation. It's likely to be a misplaced parenthesis. And
after making the if condition broken into a likely() && unlikely(), both
now appear to be correct!
Link: https://lkml.kernel.org/r/20231201145936.5ddfdb50@xxxxxxxxxxxxxxxxxx
Fixes:fb3d824d1a46c ("mm/rmap: split page_dup_rmap() into page_dup_file_rmap() and page_try_dup_anon_rmap()")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/rmap.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -250,8 +250,8 @@ static inline int page_try_dup_anon_rmap
* guarantee the pinned page won't be randomly replaced in the
* future on write faults.
*/
- if (likely(!is_device_private_page(page) &&
- unlikely(page_needs_cow_for_dma(vma, page))))
+ if (likely(!is_device_private_page(page)) &&
+ unlikely(page_needs_cow_for_dma(vma, page)))
return -EBUSY;
ClearPageAnonExclusive(page);
Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are
queue-6.1/mm-rmap-fix-misplaced-parenthesis-of-a-likely.patch
