From 5adaaa28be8a79ddd7e103b171f9d6e14e7fc26e Mon Sep 17 00:00:00 2001 From: SJ Park Date: Tue, 14 Jul 2026 20:10:01 -0700 Subject: [PATCH] mm/damon/sysfs: read ops_id only once in damon_sysfs_apply_inputs() 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. Link: https://lore.kernel.org/20260715031002.108504-7-sj@kernel.org Link: https://lore.kernel.org/20260703172417.95426-1-sj@kernel.org [1] Fixes: 8d009da32f13 ("mm/damon/sysfs: set damon_ctx->min_sz_region only for paddr use case") Signed-off-by: SJ Park Cc: # 6.18.x Signed-off-by: Andrew Morton --- mm/damon/sysfs.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index 3db4da88fc72..e3858ffab4b2 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -2094,14 +2094,16 @@ static inline bool damon_sysfs_kdamond_running( 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;