[PATCH mm-unstable 1/2] mm/damon/sysfs-schemes: skip tried regions update if the scheme directory has removed

[SeongJae Park <sj@kernel.org>]

A DAMON sysfs interface user can start DAMON with a scheme, remove the
sysfs directory for the scheme, and then ask updates of the scheme's
tried regions.  Because the schemes tried regions update logic doesn't
aware of the situation, it results in an invalid memory access.  Fix the
bug by checking if the scheme sysfs directory exists.

Fixes: 1322c8148dfe ("mm/damon/sysfs: implement DAMOS tried regions update command") # mm-unstable
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index a79aa32d3422..4df3c99983e8 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1231,6 +1231,11 @@ static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
 			break;
 		schemes_idx++;
 	}
+
+	/* user could removed the scheme sysfs dir */
+	if (schemes_idx >= sysfs_schemes->nr)
+		return 0;
+
 	sysfs_regions = sysfs_schemes->schemes_arr[schemes_idx]->tried_regions;
 	region = damon_sysfs_scheme_region_alloc(r);
 	list_add_tail(&region->list, &sysfs_regions->regions_list);
-- 
2.25.1