blk-cgroup: fix list corruption from reorder of WRITE ->lqueued

[linux-block.git] / block / blk-cgroup.c

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 8699f193cf315dbe668794a2aba0c77a6696a675..52367a4501d0339708282fe5c72681665adf0c68 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1035,6 +1035,16 @@ 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 */