6.6-stable review patch. If anyone has any objections, please let me know.
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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 9359b57545d22..8102a23b24871 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 */