[PATCH 6.9 226/374] blk-cgroup: fix list corruption from reorder of WRITE ->lqueued

Greg Kroah-Hartman
2024-06-06T14:10:16Z

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit d0aac2363549e12cc79b8e285f13d5a9f42fd08e ]

__blkcg_rstat_flush() can be run anytime, especially when blk_cgroup_bio_start
is being executed.

If WRITE of `->lqueued` is re-ordered with READ of 'bisc->lnode.next' in
the loop of __blkcg_rstat_flush(), `next_bisc` can be assigned with one
stat instance being added in blk_cgroup_bio_start(), then the local
list in __blkcg_rstat_flush() could be corrupted.

Fix the issue by adding one barrier.

Cc: Tejun Heo <tj@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20240515013157.443672-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-cgroup.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 86752b1652b5b..b36ba1d40ba1d 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1036,6 +1036,16 @@ static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu)
struct blkg_iostat cur;
unsigned int seq;

+ /*
+ * Order assignment of `next_bisc` from `bisc->lnode.next` in
+ * llist_for_each_entry_safe and clearing `bisc->lqueued` for
+ * avoiding to assign `next_bisc` with new next pointer added
+ * in blk_cgroup_bio_start() in case of re-ordering.
+ *
+ * The pair barrier is implied in llist_add() in blk_cgroup_bio_start().
+ */
+ smp_mb();
+
WRITE_ONCE(bisc->lqueued, false);

/* fetch the current per-cpu values */
--
2.43.0