FAILED: patch "[PATCH] mm/damon/ops-common: call folio_test_lru() after folio_get()" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] mm/damon/ops-common: call folio_test_lru() after folio_get()" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026061532-emu-stopped-b17a@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef Mon Sep 17 00:00:00 2001
From: SeongJae Park <sj@kernel.org>
Date: Mon, 25 May 2026 09:22:55 -0700
Subject: [PATCH] mm/damon/ops-common: call folio_test_lru() after folio_get()

damon_get_folio() speculatively calls folio_test_lru() before
folio_try_get().  The folio can get freed and reallocated to a tail page.
In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered.
Remove the speculative call.

Also mark folio_test_lru() check right after folio_try_get() success as no
more unlikely.

The race should be rare.  Also the problem can happen only if the kernel
has enabled CONFIG_DEBUG_VM_PGFLAGS.  No real world report of this issue
has been made so far.  This fix is based on only theoretical analysis.
That said, a bug is a bug.  A similar issue was also fixed via commit
3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a
reference in next_uptodate_folio()").  I don't expect this change will
make a meaningful impact to DAMON performance in the real world, though I
will be happy to be corrected from the real world reports.

The issue was discovered [1] by Sashiko.


Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org
Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1]
Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Fernand Sieber <sieberf@amazon.com>
Cc: Leonard Foerster <foersleo@amazon.de>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index 8c6d613425c1..c3e4c871b0bb 100644
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -32,9 +32,9 @@ struct folio *damon_get_folio(unsigned long pfn)
 		return NULL;
 
 	folio = page_folio(page);
-	if (!folio_test_lru(folio) || !folio_try_get(folio))
+	if (!folio_try_get(folio))
 		return NULL;
-	if (unlikely(page_folio(page) != folio || !folio_test_lru(folio))) {
+	if (unlikely(page_folio(page) != folio) || !folio_test_lru(folio)) {
 		folio_put(folio);
 		folio = NULL;
 	}

[PATCH 5.15.y] mm/damon/ops-common: call folio_test_lru() after folio_get()

[Sasha Levin]

From: SeongJae Park <sj@kernel.org>

[ Upstream commit d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef ]

damon_get_folio() speculatively calls folio_test_lru() before
folio_try_get().  The folio can get freed and reallocated to a tail page.
In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered.
Remove the speculative call.

Also mark folio_test_lru() check right after folio_try_get() success as no
more unlikely.

The race should be rare.  Also the problem can happen only if the kernel
has enabled CONFIG_DEBUG_VM_PGFLAGS.  No real world report of this issue
has been made so far.  This fix is based on only theoretical analysis.
That said, a bug is a bug.  A similar issue was also fixed via commit
3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a
reference in next_uptodate_folio()").  I don't expect this change will
make a meaningful impact to DAMON performance in the real world, though I
will be happy to be corrected from the real world reports.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org
Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1]
Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Fernand Sieber <sieberf@amazon.com>
Cc: Leonard Foerster <foersleo@amazon.de>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/damon/vaddr.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 6d8036671e60e5..dbb0f0fb2e598c 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -383,10 +383,10 @@ static struct page *damon_get_page(unsigned long pfn)
 {
 	struct page *page = pfn_to_online_page(pfn);
 
-	if (!page || !PageLRU(page) || !get_page_unless_zero(page))
+	if (!page || !get_page_unless_zero(page))
 		return NULL;
 
-	if (unlikely(!PageLRU(page))) {
+	if (!PageLRU(page)) {
 		put_page(page);
 		page = NULL;
 	}
-- 
2.53.0

Re: [PATCH 5.15.y] mm/damon/ops-common: call folio_test_lru() after folio_get()

[SeongJae Park]

On Mon, 15 Jun 2026 15:37:31 -0400 Sasha Levin <sashal@kernel.org> wrote:

> From: SeongJae Park <sj@kernel.org>
> 
> [ Upstream commit d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef ]
> 
> damon_get_folio() speculatively calls folio_test_lru() before
> folio_try_get().  The folio can get freed and reallocated to a tail page.
> In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered.
> Remove the speculative call.
> 
> Also mark folio_test_lru() check right after folio_try_get() success as no
> more unlikely.
> 
> The race should be rare.  Also the problem can happen only if the kernel
> has enabled CONFIG_DEBUG_VM_PGFLAGS.  No real world report of this issue
> has been made so far.  This fix is based on only theoretical analysis.
> That said, a bug is a bug.  A similar issue was also fixed via commit
> 3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a
> reference in next_uptodate_folio()").  I don't expect this change will
> make a meaningful impact to DAMON performance in the real world, though I
> will be happy to be corrected from the real world reports.
> 
> The issue was discovered [1] by Sashiko.
> 
> Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org
> Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1]
> Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces")
> Signed-off-by: SeongJae Park <sj@kernel.org>
> Cc: Fernand Sieber <sieberf@amazon.com>
> Cc: Leonard Foerster <foersleo@amazon.de>
> Cc: Shakeel Butt <shakeel.butt@linux.dev>
> Cc: <stable@vger.kernel.org> # 5.15.x
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>

Thank you for fixing the conflict, Sasha!

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

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