[RFC PATCH 0/9] mm/damon/sysfs: kobject_del() directories that users can create/remove

[RFC PATCH 0/9] mm/damon/sysfs: kobject_del() directories that users can create/remove

[SeongJae Park]

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.
    [...]

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.

Patches Sequence
================

There are eleven kobject_del() lacking nr_* files that are introduced by
nine different commits.  Fix each of the commits in the introduced
order.

SeongJae Park (9):
  mm/damon/sysfs: kobject_del() target, context and kdamond dirs
  mm/damon/sysfs: kobject_del() region dirs
  mm/damon/sysfs-schemes: kobject_del() scheme dirs
  mm/damon/sysfs-schemes: kobject_del() scheme region dirs
  mm/damon/sysfs-schemes: kobject_del() scheme filter dirs
  mm/damon/sysfs-schemes: kobject_del() scheme quota goal dirs
  mm/damon/sysfs-schemes: kobject_del() scheme action destination dirs
  mm/damon/sysfs: kobject_del() probe filter dirs
  mm/damon/sysfs: kobject_del() probe dirs

 mm/damon/sysfs-schemes.c | 14 +++++++++++---
 mm/damon/sysfs.c         | 12 ++++++++++--
 2 files changed, 21 insertions(+), 5 deletions(-)


base-commit: 7e1f9f51ca3090f7268c1ae8cc5b0552e9df3a87
-- 
2.47.3

[RFC PATCH 1/9] mm/damon/sysfs: kobject_del() target, context and kdamond dirs

[SeongJae Park]

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 target, context and kdamond directories by adding
kobject_del() calls.

Fixes: c951cd3b8901 ("mm/damon: implement a minimal stub for sysfs-based DAMON interface")
Cc: <stable@vger.kernel.org> # 5.18.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 2e95e3bac774d..d93f7919c3ca1 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -333,6 +333,7 @@ static void damon_sysfs_targets_rm_dirs(struct damon_sysfs_targets *targets)
 
 	for (i = 0; i < targets->nr; i++) {
 		damon_sysfs_target_rm_dirs(targets_arr[i]);
+		kobject_del(&targets_arr[i]->kobj);
 		kobject_put(&targets_arr[i]->kobj);
 	}
 	targets->nr = 0;
@@ -1642,6 +1643,7 @@ static void damon_sysfs_contexts_rm_dirs(struct damon_sysfs_contexts *contexts)
 
 	for (i = 0; i < contexts->nr; i++) {
 		damon_sysfs_context_rm_dirs(contexts_arr[i]);
+		kobject_del(&contexts_arr[i]->kobj);
 		kobject_put(&contexts_arr[i]->kobj);
 	}
 	contexts->nr = 0;
@@ -2501,6 +2503,7 @@ static void damon_sysfs_kdamonds_rm_dirs(struct damon_sysfs_kdamonds *kdamonds)
 
 	for (i = 0; i < kdamonds->nr; i++) {
 		damon_sysfs_kdamond_rm_dirs(kdamonds_arr[i]);
+		kobject_del(&kdamonds_arr[i]->kobj);
 		kobject_put(&kdamonds_arr[i]->kobj);
 	}
 	kdamonds->nr = 0;
-- 
2.47.3

[RFC PATCH 2/9] mm/damon/sysfs: kobject_del() region dirs

[SeongJae Park]

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 region directories by adding kobject_del() calls.

Fixes: 2031b14ea757 ("mm/damon/sysfs: support the physical address space monitoring")
Cc: <stable@vger.kernel.org> # 5.18.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index d93f7919c3ca1..f72e1e37df9d8 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -107,8 +107,10 @@ static void damon_sysfs_regions_rm_dirs(struct damon_sysfs_regions *regions)
 	struct damon_sysfs_region **regions_arr = regions->regions_arr;
 	int i;
 
-	for (i = 0; i < regions->nr; i++)
+	for (i = 0; i < regions->nr; i++) {
+		kobject_del(&regions_arr[i]->kobj);
 		kobject_put(&regions_arr[i]->kobj);
+	}
 	regions->nr = 0;
 	kfree(regions_arr);
 	regions->regions_arr = NULL;
-- 
2.47.3

[RFC PATCH 3/9] mm/damon/sysfs-schemes: kobject_del() scheme dirs

[SeongJae Park]

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.

Fixes: 7e84b1f8212a ("mm/damon/sysfs: support DAMON-based Operation Schemes")
Cc: <stable@vger.kernel.org> # 5.18.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 329cfd0bbe9f3..37cf6edb54f17 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2686,6 +2686,7 @@ void damon_sysfs_schemes_rm_dirs(struct damon_sysfs_schemes *schemes)
 
 	for (i = 0; i < schemes->nr; i++) {
 		damon_sysfs_scheme_rm_dirs(schemes_arr[i]);
+		kobject_del(&schemes_arr[i]->kobj);
 		kobject_put(&schemes_arr[i]->kobj);
 	}
 	schemes->nr = 0;
-- 
2.47.3

[RFC PATCH 4/9] mm/damon/sysfs-schemes: kobject_del() scheme region dirs

[SeongJae Park]

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 region directories by adding kobject_del()
calls.

This issue was discovered [1] by Sashiko, though its analysis was
partially incorrect.

[1] https://lore.kernel.org/20260517205828.6204-1-sj@kernel.org

Fixes: 9277d0367ba1 ("mm/damon/sysfs-schemes: implement scheme region directory")
Cc: <stable@vger.kernel.org> # 6.2.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 37cf6edb54f17..bf08e6e1f1635 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -334,6 +334,7 @@ static void damon_sysfs_scheme_regions_rm_dirs(
 	list_for_each_entry_safe(r, next, &regions->regions_list, list) {
 		damos_sysfs_region_rm_dirs(r);
 		list_del(&r->list);
+		kobject_del(&r->kobj);
 		kobject_put(&r->kobj);
 		regions->nr_regions--;
 	}
-- 
2.47.3

[RFC PATCH 5/9] mm/damon/sysfs-schemes: kobject_del() scheme filter dirs

[SeongJae Park]

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 filter directories by adding kobject_del()
calls.

Fixes: 472e2b70eda6 ("mm/damon/sysfs-schemes: connect filter directory and filters directory")
Cc: <stable@vger.kernel.org> # 6.3.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index bf08e6e1f1635..300930c2c5b3f 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -914,8 +914,10 @@ static void damon_sysfs_scheme_filters_rm_dirs(
 	struct damon_sysfs_scheme_filter **filters_arr = filters->filters_arr;
 	int i;
 
-	for (i = 0; i < filters->nr; i++)
+	for (i = 0; i < filters->nr; i++) {
+		kobject_del(&filters_arr[i]->kobj);
 		kobject_put(&filters_arr[i]->kobj);
+	}
 	filters->nr = 0;
 	kfree(filters_arr);
 	filters->filters_arr = NULL;
-- 
2.47.3

[RFC PATCH 6/9] mm/damon/sysfs-schemes: kobject_del() scheme quota goal dirs

[SeongJae Park]

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 quota goal directories by adding kobject_del()
calls.

Fixes: 7f262da0a30d ("mm/damon/sysfs-schemes: implement files for scheme quota goals setup")
Cc: <stable@vger.kernel.org> # 6.8.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 300930c2c5b3f..737638be84f15 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1465,8 +1465,10 @@ static void damos_sysfs_quota_goals_rm_dirs(
 	struct damos_sysfs_quota_goal **goals_arr = goals->goals_arr;
 	int i;
 
-	for (i = 0; i < goals->nr; i++)
+	for (i = 0; i < goals->nr; i++) {
+		kobject_del(&goals_arr[i]->kobj);
 		kobject_put(&goals_arr[i]->kobj);
+	}
 	goals->nr = 0;
 	kfree(goals_arr);
 	goals->goals_arr = NULL;
-- 
2.47.3

[RFC PATCH 7/9] mm/damon/sysfs-schemes: kobject_del() scheme action destination dirs

[SeongJae Park]

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 action destination directories by adding
kobject_del() calls.

Fixes: 2cd0bf85a203 ("mm/damon/sysfs-schemes: implement DAMOS action destinations directory")
Cc: <stable@vger.kernel.org> # 6.17.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 737638be84f15..108f6de32f8c1 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2148,8 +2148,10 @@ static void damos_sysfs_dests_rm_dirs(
 	struct damos_sysfs_dest **dests_arr = dests->dests_arr;
 	int i;
 
-	for (i = 0; i < dests->nr; i++)
+	for (i = 0; i < dests->nr; i++) {
+		kobject_del(&dests_arr[i]->kobj);
 		kobject_put(&dests_arr[i]->kobj);
+	}
 	dests->nr = 0;
 	kfree(dests_arr);
 	dests->dests_arr = NULL;
-- 
2.47.3

[RFC PATCH 8/9] mm/damon/sysfs: kobject_del() probe filter dirs

[SeongJae Park]

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 data attribute probe filter directories by adding
kobject_del() calls.

Fixes: 82e66aef7714 ("mm/damon/sysfs: implement filter dir")
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index f72e1e37df9d8..04725ff3d9f3c 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -960,8 +960,10 @@ static void damon_sysfs_filters_rm_dirs(struct damon_sysfs_filters *filters)
 	struct damon_sysfs_filter **filters_arr = filters->filters_arr;
 	int i;
 
-	for (i = 0; i < filters->nr; i++)
+	for (i = 0; i < filters->nr; i++) {
+		kobject_del(&filters_arr[i]->kobj);
 		kobject_put(&filters_arr[i]->kobj);
+	}
 	filters->nr = 0;
 	kfree(filters_arr);
 	filters->filters_arr = NULL;
-- 
2.47.3

[RFC PATCH 9/9] mm/damon/sysfs: kobject_del() probe dirs

[SeongJae Park]

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 data attribute probe directories by adding
kobject_del() calls.

Fixes: bf3ea3d30880 ("mm/damon/sysfs: implement probe dir")
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 04725ff3d9f3c..04ca0a34e1206 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1139,6 +1139,7 @@ static void damon_sysfs_probes_rm_dirs(
 
 	for (i = 0; i < probes->nr; i++) {
 		damon_sysfs_probe_rm_dirs(probes_arr[i]);
+		kobject_del(&probes_arr[i]->kobj);
 		kobject_put(&probes_arr[i]->kobj);
 	}
 	probes->nr = 0;
-- 
2.47.3