[PATCH v2 2/2] memcg: Don't trigger hung task warnings when memcg is releasing resources.

[Julian Sun]

Hung task warning in mem_cgroup_css_free() is undesirable and
unnecessary since the behavior of waiting for a long time is
expected.

Use touch_hung_task_detector() to eliminate the possible
hung task warning.

Signed-off-by: Julian Sun <sunjunchao@xxxxxxxxxxxxx>
---

 I didn’t add a fixes tag because there is no actual bug in the
 original code, and this patch is more of an improvement-type one.

 mm/memcontrol.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8dd7fbed5a94..fc73a56372a4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -63,6 +63,7 @@
 #include <linux/seq_buf.h>
 #include <linux/sched/isolation.h>
 #include <linux/kmemleak.h>
+#include <linux/nmi.h>
 #include "internal.h"
 #include <net/sock.h>
 #include <net/ip.h>
@@ -3912,8 +3913,15 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
 	int __maybe_unused i;
 
 #ifdef CONFIG_CGROUP_WRITEBACK
-	for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++)
+	for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) {
+		/*
+		 * We don't want the hung task detector to report warnings
+		 * here since there's nothing wrong if the writeback work
+		 * lasts for a long time.
+		 */
+		touch_hung_task_detector(current);
 		wb_wait_for_completion(&memcg->cgwb_frn[i].done);
+	}
 #endif
 	if (cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgroup_memory_nosocket)
 		static_branch_dec(&memcg_sockets_enabled_key);
-- 
2.39.5