mm/damon/core: filter out damos address filter-split failed region
Subsystems (3)
SJ Park
maintainerRFC PATCH v2 1/1 mm/damon/core: filter out damos address filter-split failed region
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.
[1] https://lore.kernel.org/[email protected]
---
Changes from RFC
- RFC: https://lore.kernel.org/[email protected]
- Handle failure in another split operation in damos_filter_match().
mm/damon/core.c | 16 ++++++++++++---- mm/damon/tests/core-kunit.h | 11 ++++++----- 2 files changed, 18 insertions(+), 9 deletions(-)
mm/damon/core.c +12 -4
@@ -2551,13 +2551,14 @@ static void damos_update_stat(struct damos *s,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 damon_ctx *ctx, struct damon_target *t, }/* 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 damon_ctx *ctx, struct damon_target *t, 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 +6 -5
@@ -1783,6 +1783,7 @@ static void damos_test_filter_out(struct kunit *test)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 kunit *test)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 kunit *test) 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 );
base-commit: 7e7e74286672b8e164e60aec0e94f05f62eb357e
Signature · 1 line
2.47.3
[email protected]
AI reviewSashiko has reviewed this patch and found no issues.
Quoted 18 lines
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.
Quoted 7 lines
The issue was discovered [1] by sashiko.
[1] https://lore.kernel.org/[email protected]
Fixes ab9bda001b68 ("mm/damon/core: introduce address range type damos filter")Cc <[email protected]> # 6.6.xSigned-off-by SJ Park <[email protected]>
Sashiko has reviewed this patch and found no issues.
Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1