[PATCH] cgroup/dmem: return error when failing to set dmem.max

[Thadeu Lima de Souza Cascardo <cascardo@igalia.com>]

page_counter_set_max may return -EBUSY in case the current usage is above
the new max. When writing to dmem.max, this error is ignored and the new
max is not set.

Return as soon as setting one of the regions max limit fails. This keeps
with the current behavior of returning when one of the region names is not
valid.

After this fix, setting a max value below the current value returns -EBUSY.

 # cat dmem.current
 drm/0000:04:00.0/vram 1060864
 # echo drm/0000:04:00.0/vram 0 > dmem.max
 -bash: echo: write error: Device or resource busy
 #

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
---
 kernel/cgroup/dmem.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
index 9d95824dc6fa09422274422313b63c25986596de..3e6d4c0b26a1f972b6c6e875f274a091fc9e2b75 100644
--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c
@@ -144,22 +144,24 @@ static void free_cg_pool(struct dmem_cgroup_pool_state *pool)
 	dmemcg_pool_put(pool);
 }
 
-static void
+static int
 set_resource_min(struct dmem_cgroup_pool_state *pool, u64 val)
 {
 	page_counter_set_min(&pool->cnt, val);
+	return 0;
 }
 
-static void
+static int
 set_resource_low(struct dmem_cgroup_pool_state *pool, u64 val)
 {
 	page_counter_set_low(&pool->cnt, val);
+	return 0;
 }
 
-static void
+static int
 set_resource_max(struct dmem_cgroup_pool_state *pool, u64 val)
 {
-	page_counter_set_max(&pool->cnt, val);
+	return page_counter_set_max(&pool->cnt, val);
 }
 
 static u64 get_resource_low(struct dmem_cgroup_pool_state *pool)
@@ -726,7 +728,7 @@ static int dmemcg_parse_limit(char *options, struct dmem_cgroup_region *region,
 
 static ssize_t dmemcg_limit_write(struct kernfs_open_file *of,
 				 char *buf, size_t nbytes, loff_t off,
-				 void (*apply)(struct dmem_cgroup_pool_state *, u64))
+				 int (*apply)(struct dmem_cgroup_pool_state *, u64))
 {
 	struct dmemcg_state *dmemcs = css_to_dmemcs(of_css(of));
 	int err = 0;
@@ -773,7 +775,7 @@ static ssize_t dmemcg_limit_write(struct kernfs_open_file *of,
 		}
 
 		/* And commit */
-		apply(pool, new_limit);
+		err = apply(pool, new_limit);
 		dmemcg_pool_put(pool);
 
 out_put:

---
base-commit: f338e77383789c0cae23ca3d48adcc5e9e137e3c
change-id: 20260318-dmem_max_ebusy-bfd33564f2c3

Best regards,
-- 
Thadeu Lima de Souza Cascardo <cascardo@igalia.com>