mm-damon-sysfs-read-ops_id-only-once-in-damon_sysfs_apply_inputs.patch removed from -mm tree

The quilt patch titled
Subject: mm/damon/sysfs: read ops_id only once in damon_sysfs_apply_inputs()
has been removed from the -mm tree. Its filename was
mm-damon-sysfs-read-ops_id-only-once-in-damon_sysfs_apply_inputs.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: SJ Park <[email protected]>
Subject: mm/damon/sysfs: read ops_id only once in damon_sysfs_apply_inputs()
Date: Tue, 14 Jul 2026 20:10:01 -0700

damon_sysfs_apply_inputs() reads ops_id twice. It could race with ops_id_store(). As a result, the min_region_sz could wrongly be set up. Read it once.

The user impact is trivial. Sane users ain't update the parameter in parallel. Even if it happens, the DAMON core layer handles the wrong min_region_sz (!is_power_of_2()). Even if somehow the race ended up making a min_region_sz that is different from the user's intention but still valid, only monitoring itself runs differently than expected. No critical consequences like kernel panic or memory corruption happen

The issue was discovered [1] by Sashiko.

---

 mm/damon/sysfs.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -2094,14 +2094,16 @@ static inline bool damon_sysfs_kdamond_r
 static int damon_sysfs_apply_inputs(struct damon_ctx *ctx,
 		struct damon_sysfs_context *sys_ctx)
 {
+	enum damon_ops_id ops_id;
 	int err;
 
-	err = damon_select_ops(ctx, sys_ctx->ops_id);
+	ops_id = READ_ONCE(sys_ctx->ops_id);
+	err = damon_select_ops(ctx, ops_id);
 	if (err)
 		return err;
 	ctx->addr_unit = READ_ONCE(sys_ctx->addr_unit);
 	/* addr_unit is respected by only DAMON_OPS_PADDR */
-	if (sys_ctx->ops_id == DAMON_OPS_PADDR)
+	if (ops_id == DAMON_OPS_PADDR)
 		ctx->min_region_sz = max(
 				DAMON_MIN_REGION_SZ / ctx->addr_unit, 1);
 	ctx->pause = sys_ctx->pause;

_

Patches currently in -mm which might be from [email protected] are