kernel/git/stable/linux.git/mm, branch linux-6.1.y

mm/damon/core: skip aging from repeated aggressive merging

2026-09-14T11:24:34+00:00

[ Upstream commit 0250dbe08c730d003ef9f484da56ae09a1ea0c4c ] The number of DAMON regions could temporarily exceed the user-defined maximum number of regions limit for corner cases. For example, users could lower the limit via runtime parameters update. For such a case, kdamond_merge_regions() repeats merging regions in the case doubling the merge threshold. The repeated merge operation could update the age of regions multiple times. This corrupts the monitoring results. Fix the issue by asking the merge operation to skip aging for the corner case. The user impact is degradation of the monitoring quality. The impact should be mild, since the degradation is only temporal, and it is not common to happen in realistic setups. The issue was discovered [1,2] by Sashiko. Link: https://lore.kernel.org/20260712165432.87609-1-sj@kernel.org Link: https://lore.kernel.org/20260621203548.10718-1-sj@kernel.org [1] Link: https://lore.kernel.org/20260709145425.96247-1-sj@kernel.org [2] Fixes: 310d6c15e910 ("mm/damon/core: merge regions aggressively when max_nr_regions is unmet") Signed-off-by: SJ Park Cc: # 6.10 Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin

mm/damon/tests/core-kunit: catch test failure in test_merge_regions_of()

2026-09-14T11:24:33+00:00

[ Upstream commit b640708929aa956235866bf7717d89018c661083 ] KUNIT_EXPECT_EQ() does not abort the execution of test code when the expectation is not met. But damon_test_merge_regions_of() code after its initial KUNIT_EXPECT_EQ() call assumes the expectation is met. It does a per-region test with a hard-coded number of regions that is correct only if the expectation was met. As a result, __nth_region_of() could return NULL, and the test code can dereference NULL pointers. Fix the issue by catching the expectation failure and skip the per-region tests. The user impact on realistic setups should be negligible, as it is a unit test. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260715031002.108504-3-sj@kernel.org Link: https://lore.kernel.org/20260710144937.26981-1-sj@kernel.org [1] Fixes: 17ccae8bb5c9 ("mm/damon: add kunit tests") Signed-off-by: SJ Park Cc: # 5.15.x Signed-off-by: Andrew Morton Signed-off-by: SJ Park Signed-off-by: Sasha Levin

mm/damon/sysfs-schemes: kobject_del() scheme dirs

2026-09-14T11:24:32+00:00

[ Upstream commit 05fb6ac98c49be870c5f9ccdfdf95f0107e564ae ] On CONFIG_DEBUG_KOBJECT_RELEASE enabled kernel, lack of kobject_del() could cause directories creation failures due to the name conflicts. Fix those issues for scheme directories by adding kobject_del() calls. Link: https://lore.kernel.org/20260628220121.97360-4-sj@kernel.org Fixes: 7e84b1f8212a ("mm/damon/sysfs: support DAMON-based Operation Schemes") Signed-off-by: SJ Park Cc: # 5.18.x Signed-off-by: Andrew Morton Signed-off-by: SJ Park Signed-off-by: Sasha Levin

mm/damon/vaddr-kunit: check region count in three_regions test

2026-09-14T11:24:32+00:00

[ Upstream commit 5fea07e460874c8c7cf00f728efbe22abc62c8d8 ] damon_do_test_apply_three_regions() iterates regions after damon_set_regions() call assuming the function would succeed at setting the number of regions the same to the expected one. It might have failed. In this case, __nth_region_of() in the iteration could return NULL and NULL dereference can happen in the test. The consequent user impact (NULL dereference) is quite bad. The realistic user impact would be limited, though. It would affect only test run setups. Fix it by testing if the number of regions was also changed as expected and exit early for the failure. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260718001442.87129-4-sj@kernel.org Link: https://lore.kernel.org/20260713144757.39740-1-sj@kernel.org [1] Fixes: 17ccae8bb5c9 ("mm/damon: add kunit tests") Signed-off-by: SJ Park Cc: Brendan Higgins Cc: # 5.15.x Signed-off-by: Andrew Morton Signed-off-by: SJ Park Signed-off-by: Sasha Levin

mm/damon/paddr: drop last same folio access check reuse optimization

2026-09-14T11:24:32+00:00

[ Upstream commit f23f0aa62b2f32c2b12f95959fc4603ef81678b2 ] It can race when multiple kdamonds are being used. The problem from the race is doubtful, but the gain from the optimization is also doubtful. Simply drop the optimization in favor of code simplicity. The user impact is doubtfully trivial. After all, this kind of interference can happen only by intentional user setup. Even if it happens, it will be rare, and the consequence is degradation of the best-effort monitoring results. No critical consequences like kernel panic or memory corruption happen. The race was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260715031002.108504-5-sj@kernel.org Link: https://lore.kernel.org/20260621204050.10993-1-sj@kernel.org [1] Fixes: a28397beb55b ("mm/damon: implement primitives for physical address space monitoring") Signed-off-by: SJ Park Cc: # 5.16.x Signed-off-by: Andrew Morton Signed-off-by: SJ Park Signed-off-by: Sasha Levin

mm/damon/vaddr: drop last same folio access check optimization

2026-09-14T11:24:32+00:00

[ Upstream commit 831846078caa14b7d00b2ccca8b8fe522afe3204 ] The optimization can race when multiple kdamonds are running. Meanwhile, the impact of the optimization is quite doubtful. Just remove it. The user impact of the issue should be quite trivial. After all, the race can happen only when the user intentionally setup DAMON in the way. Even if it happens, it would be rare and only degrade the best-effort monitoring results. No critical consequences like kernel panic or memory corruption happen. The race possibility was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260715031002.108504-4-sj@kernel.org Link: https://lore.kernel.org/20260621204050.10993-1-sj@kernel.org [1] Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") Signed-off-by: SJ Park Cc: # 5.15.x Signed-off-by: Andrew Morton Signed-off-by: SJ Park Signed-off-by: Sasha Levin

mm/damon/core-kunit: check region count before testing in split_at()

2026-09-14T11:24:32+00:00

[ Upstream commit 9b18ef3c3aa1ce24176e340061caf15fa2742564 ] damon_test_split_at() test next region that is assumed to be created by damon_split_region_at() invocation. But the split might fail. In this case, the succeeding test may dereference invalid pointers returned by damon_next_region(). The invalid pointer may not cause a really bad user impact, because of the implementation detail. It would only read wrong contents in the belonging damon_target struct. Depending on the future change of the offset from the link header to the accessing field, this could also be really dangerous, though. Still, the realistic user impact would be limited. It would affect only test run setups. Fix it by testing if the number of regions was also changed as expected and exit early for the failure. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260718001442.87129-3-sj@kernel.org Link: https://lore.kernel.org/20260714142352.100478-1-sj@kernel.org [1] Fixes: 17ccae8bb5c9 ("mm/damon: add kunit tests") Signed-off-by: SJ Park Cc: Brendan Higgins Cc: # 5.15.x Signed-off-by: Andrew Morton Signed-off-by: SJ Park Signed-off-by: Sasha Levin

mm/hugetlb: fix missing migratable flag on same-node hugetlb migration

2026-09-14T11:24:24+00:00

commit 8ee1ef0f2f8ce29338f4ab00a3d344c010208058 upstream. Commit ba23f58de896 ("mm/migrate: don't call folio_putback_active_hugetlb() on dst hugetlb folio") moved setting of the migratable flag and active-list placement from folio_putback_active_hugetlb(dst) into move_hugetlb_state(), so that the freshly allocated destination folio is handled where allocation is known to have succeeded. Unfortunately, the new code was appended after the existing temporary-folio block in move_hugetlb_state(), which contains an early return added earlier by commit 5af1ab1d24e08 ("mm/hugetlb: optimize the surplus state transfer code in move_hugetlb_state()"): if (folio_test_hugetlb_temporary(new_folio)) { ... if (new_nid == old_nid) return; <-- skips the new code ... } /* added by ba23f58 */ folio_set_hugetlb_migratable(new_folio); list_move_tail(&new_folio->lru, ...&h->hugepage_activelist); When the destination folio is temporary (i.e. the hugetlb pool was exhausted and the migration callback fell back to alloc_migrate_hugetlb_folio()) and the migration does not cross a node -- the common case, and always true on a single-NUMA system -- move_hugetlb_state() returns before setting the migratable flag or adding the new folio to the active list. The destination folio is then installed in the page table but cannot be isolated afterwards, since folio_isolate_hugetlb() rejects folios without the migratable flag; a subsequent soft-offline, hard-offline or memory-hotplug offline of that folio fails with -EBUSY. This was reproduced on a single-NUMA arm64 VM: a second MADV_SOFT_OFFLINE on an already-migrated hugetlb page returned EBUSY and logged "hugepage isolation failed". Keep the surplus adjustment, which is the only part that depends on the node crossing, guarded by `if (new_nid != old_nid)', while making the migratable flag and active-list placement unconditional. This preserves the cleanup intent of ba23f58 and closes the early-return hole. Link: https://lore.kernel.org/20260707110254.3147686-1-mawupeng1@huawei.com Fixes: ba23f58de896 ("mm/migrate: don't call folio_putback_active_hugetlb() on dst hugetlb folio") Signed-off-by: Wupeng Ma Acked-by: David Hildenbrand (Arm) Cc: Baolin Wang Cc: Muchun Song Cc: Oscar Salvador Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

mm/damon/sysfs: kobject_del() target (normal), context and kdamond dirs

2026-09-14T11:24:23+00:00

commit 263af33a72d1995ae6cdc22b08d527e2bda17259 upstream. Patch series "mm/damon/sysfs: kobject_del() directories that users can create/remove". DAMON sysfs interface allows users to create and remove arbitrary number of directories on sysfs, using a few files having 'nr_' prefix. For example, 'nr_kdamonds'. When the user writes a number 'N' to the files, directories having name starting from '0' to 'N - 1' are created in the same directory. The pre-existing number-named directories are removed before creating the new directories. For the removal of the existing directories, DAMON sysfs interface use only kobject_put(). Because DAMON sysfs interface is the only kernel component that manages the directories, there is no problem in normal situations. However, if CONFIG_DEBUG_KOBJECT_RELEASE is enabled, the removal of dirs are delayed. Let's suppose a user writes a non-zero number to the 'nr_*' files while there are pre-existing number-named directories, on the config enabled kernel. DAMON sysfs interface decreases the reference counts of the existing directories and immediately creates new directories. Because the removal of the sysfs directories is delayed, it shows some pre-existing directories of the same names when it tries to create the new directories, and fails. For example, the issue can be triggered like below: # grep DEBUG_KOBJECT_RELEASE /boot/config-$(uname -r) CONFIG_DEBUG_KOBJECT_RELEASE=y # ls nr_kdamonds # echo 1 > nr_kdamonds # echo 1 > nr_kdamonds bash: echo: write error: File exists # dmesg [...] [ 300.880458] kobject: kobject_add_internal failed for 0 with -EEXIST, don't try to register things with the same name in the same directory. [...] Some of the error handling paths of the directories also lack the kobject_del() call. If the user uses nr_* file right after the errors, similar issues can happen. This doesn't cause catastrophic issues like kernel panics or memory corruptions. Users can work around by removing all directories first (write 0 to the nr_* files) and then create new directories after confirming the old directories are gone. But, this is definitely a bug that causes a bad user experience. Fix the issues by calling kobject_del() before creating new directories. This patch (of 11) On CONFIG_DEBUG_KOBJECT_RELEASE enabled kernel, lack of kobject_del() could cause directories creation failures due to the name conflicts. Fix those issues for normal creation paths of target, context and kdamond directories, and error paths of context and kdamond directories by adding kobject_del() calls. Note that this fix for target directories is not complete since it has a similar issue in the damon_sysfs_targets_add_dirs() error path. Because the normal path issue and the error path issue are introduced by different commits, this commit is fixing only the normal path issue. A commit for the error path will be added next. Link: https://lore.kernel.org/20260628220121.97360-1-sj@kernel.org Link: https://lore.kernel.org/20260628220121.97360-2-sj@kernel.org Fixes: c951cd3b8901 ("mm/damon: implement a minimal stub for sysfs-based DAMON interface") Signed-off-by: SJ Park Cc: # 5.18.x Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

mm/damon/sysfs: kobject_del() region and target (error) dirs

2026-09-14T11:24:23+00:00

commit 2603ef6f6ec3d3f7de2d6a07e7c9a683cebac419 upstream. On CONFIG_DEBUG_KOBJECT_RELEASE enabled kernel, lack of kobject_del() could cause directories creation failures due to the name conflicts. Fix those issues for the normal creation path of region directories and the error path of target directories, by adding kobject_del() calls. Link: https://lore.kernel.org/20260628220121.97360-3-sj@kernel.org Fixes: 2031b14ea757 ("mm/damon/sysfs: support the physical address space monitoring") Signed-off-by: SJ Park Cc: # 5.18.x Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman