mm-damon-core-filter-out-damos-address-filter-split-failed-region.patch removed from -mm tree

merged mm-stable Andrew Morton 1 participant 1 message Oct 24 Stable branch

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2026-10-24 09:02 UTC #0 lore raw

The quilt patch titled
Subject: mm/damon/core: filter out damos address filter-split failed region
has been removed from the -mm tree. Its filename was
mm-damon-core-filter-out-damos-address-filter-split-failed-region.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: SJ Park <[email protected]>
Subject: mm/damon/core: filter out damos address filter-split failed region
Date: Mon, 19 Oct 2026 17:41:18 -0700

When an address type DAMOS filter is configured, DAMOS tries to split the region for the filter range, and apply DAMOS action to the filter-in region. The split operation (damon_split_region_at()) could fail from allocation failure under extreme memory pressure. In the case, DAMOS action could be applied more or less than expected, ignoring the address filter.

The issue only rarely happens under extreme memory pressure. No crash or leak happens. Occasionally not applying the action to a few regions shouldn't be a real problem. But applying the action to a region that the user has excluded via address filter could be a surprise depending on the use case. It is only theoretical. No such real case is found yet.

Filter out the entire region if the split is failed. Update damos_filter_match() signature to receive the error from split. Also update kunit tests for the updated signature.

The issue was discovered [1] by sashiko.

Link https://lore.kernel.org/[email protected] open here

Link https://lore.kernel.org/[email protected] [1] open here

Fixes ab9bda001b68 ("mm/damon/core: introduce address range type damos filter")

Signed-off-by SJ Park <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

Cc <[email protected]> # 6.6.x

---

 mm/damon/core.c             |   16 ++++++++++++----
 mm/damon/tests/core-kunit.h |   11 ++++++-----
 2 files changed, 18 insertions(+), 9 deletions(-)

mm/damon/core.c renamed from mm/damon/core.c~mm-damon-core-filter-out-damos-address-filter-split-failed-region +12 -4

@@ -2551,13 +2551,14 @@ static void damos_update_stat(struct dam
 
 static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t,
 		struct damon_region *r, struct damos_filter *filter,
-		unsigned long min_region_sz)
+		unsigned long min_region_sz, int *err)
 {
 	bool matched = false;
 	struct damon_target *ti;
 	int target_idx = 0;
 	unsigned long start, end, wsum;
 
+	*err = 0;
 	switch (filter->type) {
 	case DAMOS_FILTER_TYPE_TARGET:
 		damon_for_each_target(ti, ctx) {

@@ -2583,12 +2584,13 @@ static bool damos_filter_match(struct da
 		}
 		/* start before the range and overlap */
 		if (r->ar.start < start) {
-			damon_split_region_at(t, r, start - r->ar.start);
+			*err = damon_split_region_at(t, r,
+					start - r->ar.start);
 			matched = false;
 			break;
 		}
 		/* start inside the range */
-		damon_split_region_at(t, r, end - r->ar.start);
+		*err = damon_split_region_at(t, r, end - r->ar.start);
 		matched = true;
 		break;
 	case DAMOS_FILTER_TYPE_PROBE_HITS_WSUM:

@@ -2607,10 +2609,16 @@ static bool damos_core_filter_out(struct
 		struct damon_region *r, struct damos *s)
 {
 	struct damos_filter *filter;
+	bool matching;
+	int err;
 
 	s->core_filters_allowed = false;
 	damos_for_each_core_filter(filter, s) {
-		if (damos_filter_match(ctx, t, r, filter, ctx->min_region_sz)) {
+		matching = damos_filter_match(ctx, t, r, filter,
+				ctx->min_region_sz, &err);
+		if (err)
+			return true;
+		if (matching) {
 			if (filter->allow)
 				s->core_filters_allowed = true;
 			return !filter->allow;

mm/damon/tests/core-kunit.h renamed from mm/damon/tests/core-kunit.h~mm-damon-core-filter-out-damos-address-filter-split-failed-region +6 -5

@@ -1783,6 +1783,7 @@ static void damos_test_filter_out(struct
 	struct damon_target *t;
 	struct damon_region *r, *r2;
 	struct damos_filter *f;
+	int err;
 
 	f = damos_new_filter(DAMOS_FILTER_TYPE_ADDR, true, false);
 	if (!f)

@@ -1803,27 +1804,27 @@ static void damos_test_filter_out(struct
 	damon_add_region(r, t);
 
 	/* region in the range */
-	KUNIT_EXPECT_TRUE(test, damos_filter_match(NULL, t, r, f, 1));
+	KUNIT_EXPECT_TRUE(test, damos_filter_match(NULL, t, r, f, 1, &err));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region before the range */
 	r->ar.start = 1;
 	r->ar.end = 2;
 	KUNIT_EXPECT_FALSE(test,
-			damos_filter_match(NULL, t, r, f, 1));
+			damos_filter_match(NULL, t, r, f, 1, &err));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region after the range */
 	r->ar.start = 6;
 	r->ar.end = 8;
 	KUNIT_EXPECT_FALSE(test,
-			damos_filter_match(NULL, t, r, f, 1));
+			damos_filter_match(NULL, t, r, f, 1, &err));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region started before the range */
 	r->ar.start = 1;
 	r->ar.end = 4;
-	KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f, 1));
+	KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f, 1, &err));
 	/* filter should have split the region */
 	KUNIT_EXPECT_EQ(test, r->ar.start, 1);
 	KUNIT_EXPECT_EQ(test, r->ar.end, 2);

@@ -1839,7 +1840,7 @@ static void damos_test_filter_out(struct
 	r->ar.start = 2;
 	r->ar.end = 8;
 	KUNIT_EXPECT_TRUE(test,
-			damos_filter_match(NULL, t, r, f, 1));
+			damos_filter_match(NULL, t, r, f, 1, &err));
 	/* filter should have split the region */
 	KUNIT_EXPECT_EQ(test, r->ar.start, 2);
 	KUNIT_EXPECT_EQ(test, r->ar.end, 6);

Patches currently in -mm which might be from [email protected] are