commit ebb3f994dd92f8fb4d70c7541091216c1e10cb71 upstream.

DAMON debugfs interface increases the reference counts of 'struct pid's for targets from the 'target_ids' file write callback ('dbgfs_target_ids_write()'), but decreases the counts only in DAMON monitoring termination callback ('dbgfs_before_terminate()').

Therefore, when 'target_ids' file is repeatedly written without DAMON monitoring start/termination, the reference count is not decreased and therefore memory for the 'struct pid' cannot be freed. This commit fixes this issue by decreasing the reference counts when 'target_ids' is written.

Link: https://lkml.kernel.org/r/20211229124029.23348-1-sj@kernel.org Fixes: 4bc05954d007 ("mm/damon: implement a debugfs-based user space interface") Signed-off-by: SeongJae Park sj@kernel.org Cc: stable@vger.kernel.org # 5.15.x Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org --- This is a backport of a DAMON fix that merged in the mainline, for v5.15.x stable series.

mm/damon/dbgfs.c | 8 ++++++++ 1 file changed, 8 insertions(+)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c index d3bc110430f9..36624990b577 100644 --- a/mm/damon/dbgfs.c +++ b/mm/damon/dbgfs.c @@ -185,6 +185,7 @@ static ssize_t dbgfs_target_ids_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) { struct damon_ctx *ctx = file->private_data; + struct damon_target *t, *next_t; char *kbuf, *nrs; unsigned long *targets; ssize_t nr_targets; @@ -224,6 +225,13 @@ static ssize_t dbgfs_target_ids_write(struct file *file, goto unlock_out; }

+ /* remove previously set targets */ + damon_for_each_target_safe(t, next_t, ctx) { + if (targetid_is_pid(ctx)) + put_pid((struct pid *)t->id); + damon_destroy_target(t); + } + err = damon_set_targets(ctx, targets, nr_targets); if (err) { if (targetid_is_pid(ctx))