mm/damon/sysfs: cleanup intervals subdirs on attrs dir setup failure

commit a24ca8ebb0cd5ea07a1462b77be0f0823c40f319 upstream.

Patch series "mm/damon/sysfs: free setup failures generated zombie sub-sub
dirs".

Some DAMON sysfs directory setup functions generates its sub and sub-sub
directories.  For example, 'monitoring_attrs/' directory setup creates
'intervals/' and 'intervals/intervals_goal/' directories under
'monitoring_attrs/' directory.  When such sub-sub directories are
successfully made but followup setup is failed, the setup function should
recursively clean up the subdirectories.

However, such setup functions are only dereferencing sub directory
reference counters.  As a result, under certain setup failures, the
sub-sub directories keep having non-zero reference counters.  It means the
directories cannot be removed like zombies, and the memory for the
directories cannot be freed.

The user impact of this issue is limited due to the following reasons.

When the issue happens, the zombie directories are still taking the path.
Hence attempts to generate the directories again will fail, without
additional memory leak.  This means the upper bound memory leak is
limited.  Nonetheless this also implies controlling DAMON with a feature
that requires the setup-failed sysfs files will be impossible until the
system reboots.

Also, the setup operations are quite simple.  The certain failures would
hence only rarely happen, and are difficult to artificially trigger.

This patch (of 4):

When attrs/ DAMON sysfs directory setup is failed after setup of
intervals/ directory, intervals/intervals_goal/ directory is not cleaned
up.  As a result, DAMON sysfs interface is nearly broken until the system
reboots, and the memory for the unremoved directory is leaked.

Cleanup the directory under such failures.

Link: https://lkml.kernel.org/r/20251225023043.18579-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20251225023043.18579-2-sj@kernel.org
Fixes: 8fbbcbeaafeb ("mm/damon/sysfs: implement intervals tuning goal directory")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: chongjiapeng <jiapeng.chong@linux.alibaba.com>
Cc: <stable@vger.kernel.org> # 6.15.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 3c0d727788c87569b1ba55599c7bd093ecad28c3..2b4920a722e495c9e3f2ace8eaeae2aac9deb664 100644 (file)
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -764,7 +764,7 @@ static int damon_sysfs_attrs_add_dirs(struct damon_sysfs_attrs *attrs)
        nr_regions_range = damon_sysfs_ul_range_alloc(10, 1000);
        if (!nr_regions_range) {
                err = -ENOMEM;
-               goto put_intervals_out;
+               goto rmdir_put_intervals_out;
        }
 
        err = kobject_init_and_add(&nr_regions_range->kobj,
@@ -778,6 +778,8 @@ static int damon_sysfs_attrs_add_dirs(struct damon_sysfs_attrs *attrs)
 put_nr_regions_intervals_out:
        kobject_put(&nr_regions_range->kobj);
        attrs->nr_regions_range = NULL;
+rmdir_put_intervals_out:
+       damon_sysfs_intervals_rm_dirs(intervals);
 put_intervals_out:
        kobject_put(&intervals->kobj);
        attrs->intervals = NULL;