[PATCH mm-hotfixes-unstable] mm/damon/sysfs: fix wrong empty schemes assumption under online tuning in damon_sysfs_set_schemes()

[SeongJae Park <sj@kernel.org>]

Commit da87878010e5 ("mm/damon/sysfs: support online inputs update")
made 'damon_sysfs_set_schemes()' to be called for running DAMON context,
which could have schemes.  In the case, DAMON sysfs interface is
supposed to update, remove, or add schemes to reflect the sysfs files.
However, the code is assuming the DAMON context wouldn't have schemes at
all, and therefore creates and adds new schemes.  As a result, the code
doesn't work as intended for online schemes tuning and could have more
than expected memory footprint.   The schemes are all in the DAMON
context, so it doesn't leak the memory, though.

Remove the wrong asssumption (the DAMON context wouldn't have schemes)
in 'damon_sysfs_set_schemes()' to fix the bug.

Fixes: da87878010e5 ("mm/damon/sysfs: support online inputs update")
Cc: <stable@vger.kernel.org> # 5.19.y
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 5ce403378c20..07e5f1bdf025 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -2283,12 +2283,54 @@ static struct damos *damon_sysfs_mk_scheme(
 			&wmarks);
 }
 
+static void damon_sysfs_update_scheme(struct damos *scheme,
+		struct damon_sysfs_scheme *sysfs_scheme)
+{
+	struct damon_sysfs_access_pattern *access_pattern =
+		sysfs_scheme->access_pattern;
+	struct damon_sysfs_quotas *sysfs_quotas = sysfs_scheme->quotas;
+	struct damon_sysfs_weights *sysfs_weights = sysfs_quotas->weights;
+	struct damon_sysfs_watermarks *sysfs_wmarks = sysfs_scheme->watermarks;
+
+	scheme->pattern.min_sz_region = access_pattern->sz->min;
+	scheme->pattern.max_sz_region = access_pattern->sz->max;
+	scheme->pattern.min_nr_accesses = access_pattern->nr_accesses->min;
+	scheme->pattern.max_nr_accesses = access_pattern->nr_accesses->max;
+	scheme->pattern.min_age_region = access_pattern->age->min;
+	scheme->pattern.max_age_region = access_pattern->age->max;
+
+	scheme->action = sysfs_scheme->action;
+
+	scheme->quota.ms = sysfs_quotas->ms;
+	scheme->quota.sz = sysfs_quotas->sz;
+	scheme->quota.reset_interval = sysfs_quotas->reset_interval_ms;
+	scheme->quota.weight_sz = sysfs_weights->sz;
+	scheme->quota.weight_nr_accesses = sysfs_weights->nr_accesses;
+	scheme->quota.weight_age = sysfs_weights->age;
+
+	scheme->wmarks.metric = sysfs_wmarks->metric;
+	scheme->wmarks.interval = sysfs_wmarks->interval_us;
+	scheme->wmarks.high = sysfs_wmarks->high;
+	scheme->wmarks.mid = sysfs_wmarks->mid;
+	scheme->wmarks.low = sysfs_wmarks->low;
+}
+
 static int damon_sysfs_set_schemes(struct damon_ctx *ctx,
 		struct damon_sysfs_schemes *sysfs_schemes)
 {
-	int i;
+	struct damos *scheme, *next;
+	int i = 0;
+
+	damon_for_each_scheme_safe(scheme, next, ctx) {
+		if (i < sysfs_schemes->nr)
+			damon_sysfs_update_scheme(scheme,
+					sysfs_schemes->schemes_arr[i]);
+		else
+			damon_destroy_scheme(scheme);
+		i++;
+	}
 
-	for (i = 0; i < sysfs_schemes->nr; i++) {
+	for (; i < sysfs_schemes->nr; i++) {
 		struct damos *scheme, *next;
 
 		scheme = damon_sysfs_mk_scheme(sysfs_schemes->schemes_arr[i]);
-- 
2.25.1