FAILED: patch "[PATCH] mm/damon/core: initialize damos->last_applied" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-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 <[email protected]>.

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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x af5f76aeb9c9aa9c77d5e1d94e0ee4618c805239
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090805-evoke-tiring-a0dd@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From af5f76aeb9c9aa9c77d5e1d94e0ee4618c805239 Mon Sep 17 00:00:00 2001
From: SJ Park <[email protected]>
Date: Fri, 17 Jul 2026 17:14:35 -0700
Subject: [PATCH] mm/damon/core: initialize damos->last_applied

Patch series "mm/damon: fix uninitialized DAMOS field and kunit exec expectation bugs".

Fix a few Sashiko-found unurgent bugs. Patch 1 fixes use of uninitialized damos->last_applied field. Patches 2-7 fix DAMON kunit tests that do invalid memory access under test failures.

The bugs are better to be fixed and eventually merged into stable@ kernel. That said, the fixes are arguably not urgent. Patch 1 only introduces negligible DAMOS efficiency degradation in occasional cases. Kunit fixes could introduce quite bad consequences but those are test code that affect only test run setups.

This patch (of 7):

Multiple DAMON regions could exist across a folio. If they fulfill the condition to apply a DAMOS scheme, the scheme could be applied multiple times to the folio. To avoid this, each DAMOS scheme stores the folio that the scheme was applied to last time in the damos->last_applied field and skips repeatedly applying the same scheme to the same folio.

The field is being used without initialization, though. Hence, the mechanism could wrongly skip applying a scheme to a folio at the very first time of DAMOS run.

The user impact is trivial. DAMON might unexpectedly skip applying DAMOS action for one folio for the first time per scheme. In the DAMON's best-effort world, this is never a real problem. No critical consequences such as kernel panic or memory corruption happen.

It is a clear bug, though, and the fix is straightforward. Fix the issue by initializing the field in DAMOS scheme creation function, damon_new_scheme().

The issue was discovered [1] by Sashiko.

index 603b102ff80f..20d267c615fa 100644
@@ -705,6 +705,7 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
 	INIT_LIST_HEAD(&scheme->ops_filters);
 	scheme->stat = (struct damos_stat){};
 	scheme->max_nr_snapshots = 0;
+	scheme->last_applied = NULL;
 	INIT_LIST_HEAD(&scheme->list);
 
 	scheme->quota = *(damos_quota_init(quota));

Patch series "mm/damon: fix uninitialized DAMOS field and kunit exec expectation bugs".

Fix a few Sashiko-found unurgent bugs. Patch 1 fixes use of uninitialized damos->last_applied field. Patches 2-7 fix DAMON kunit tests that do invalid memory access under test failures.

The bugs are better to be fixed and eventually merged into stable@ kernel. That said, the fixes are arguably not urgent. Patch 1 only introduces negligible DAMOS efficiency degradation in occasional cases. Kunit fixes could introduce quite bad consequences but those are test code that affect only test run setups.

This patch (of 7):

Multiple DAMON regions could exist across a folio. If they fulfill the condition to apply a DAMOS scheme, the scheme could be applied multiple times to the folio. To avoid this, each DAMOS scheme stores the folio that the scheme was applied to last time in the damos->last_applied field and skips repeatedly applying the same scheme to the same folio.

The field is being used without initialization, though. Hence, the mechanism could wrongly skip applying a scheme to a folio at the very first time of DAMOS run.

The user impact is trivial. DAMON might unexpectedly skip applying DAMOS action for one folio for the first time per scheme. In the DAMON's best-effort world, this is never a real problem. No critical consequences such as kernel panic or memory corruption happen.

It is a clear bug, though, and the fix is straightforward. Fix the issue by initializing the field in DAMOS scheme creation function, damon_new_scheme().

The issue was discovered [1] by Sashiko.

---
 mm/damon/core.c | 1 +
 1 file changed, 1 insertion(+)

index 70ac1f08753d1..02aebbc5d98e3 100644
@@ -412,6 +412,7 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
 	INIT_LIST_HEAD(&scheme->filters);
 	INIT_LIST_HEAD(&scheme->ops_filters);
 	scheme->stat = (struct damos_stat){};
+	scheme->last_applied = NULL;
 	INIT_LIST_HEAD(&scheme->list);
 
 	scheme->quota = *(damos_quota_init(quota));

2.47.3