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

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

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>