Johannes Weiner writes:
Dan Carpenter reports:
The patch 2d146aa3aa84: "mm: memcontrol: switch to rstat" from Apr
29, 2021, leads to the following static checker warning:
kernel/cgroup/rstat.c:200 cgroup_rstat_flush()
warn: sleeping in atomic context
mm/memcontrol.c
3572 static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
3573 {
3574 unsigned long val;
3575
3576 if (mem_cgroup_is_root(memcg)) {
3577 cgroup_rstat_flush(memcg->css.cgroup);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This is from static analysis and potentially a false positive. The
problem is that mem_cgroup_usage() is called from __mem_cgroup_threshold()
which holds an rcu_read_lock(). And the cgroup_rstat_flush() function
can sleep.
3578 val = memcg_page_state(memcg, NR_FILE_PAGES) +
3579 memcg_page_state(memcg, NR_ANON_MAPPED);
3580 if (swap)
3581 val += memcg_page_state(memcg, MEMCG_SWAP);
3582 } else {
3583 if (!swap)
3584 val = page_counter_read(&memcg->memory);
3585 else
3586 val = page_counter_read(&memcg->memsw);
3587 }
3588 return val;
3589 }
__mem_cgroup_threshold() indeed holds the rcu lock. In addition, the
thresholding code is invoked during stat changes, and those contexts
have irqs disabled as well. If the lock breaking occurs inside the
flush function, it will result in a sleep from an atomic context.
Use the irsafe flushing variant in mem_cgroup_usage() to fix this.
Fixes: 2d146aa3aa84 ("mm: memcontrol: switch to rstat")
Cc: <stable@xxxxxxxxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Thanks, looks good.
Acked-by: Chris Down <chris@xxxxxxxxxxxxxx>
---
mm/memcontrol.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ae1f5d0cb581..eb8e87c4833f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3574,7 +3574,8 @@ static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
unsigned long val;
if (mem_cgroup_is_root(memcg)) {
- cgroup_rstat_flush(memcg->css.cgroup);
+ /* mem_cgroup_threshold() calls here from irqsafe context */
+ cgroup_rstat_flush_irqsafe(memcg->css.cgroup);
val = memcg_page_state(memcg, NR_FILE_PAGES) +
memcg_page_state(memcg, NR_ANON_MAPPED);
if (swap)
--
2.32.0
