6.9-stable review patch. If anyone has any objections, please let me know.
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From: Waiman Long longman@redhat.com
[ Upstream commit 9d230c09964e6e18c8f6e4f0d41ee90eef45ec1c ]
During a cgroup_rstat_flush() call, the lowest level of nodes are flushed first before their parents. Since commit 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()"), iostat propagation was still done to the parent. Grandparent, however, may not get the iostat update if the parent has no blkg_iostat_set queued in its lhead lockless list.
Fix this iostat propagation problem by queuing the parent's global blkg->iostat into one of its percpu lockless lists to make sure that the delta will always be propagated up to the grandparent and so on toward the root blkcg.
Note that successive calls to __blkcg_rstat_flush() are serialized by the cgroup_rstat_lock. So no special barrier is used in the reading and writing of blkg->iostat.lqueued.
Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()") Reported-by: Dan Schatzberg schatzberg.dan@gmail.com Closes: https://lore.kernel.org/lkml/ZkO6l%2FODzadSgdhC@dschatzberg-fedora-PF3DHTBV/ Signed-off-by: Waiman Long longman@redhat.com Reviewed-by: Ming Lei ming.lei@redhat.com Acked-by: Tejun Heo tj@kernel.org Link: https://lore.kernel.org/r/20240515143059.276677-1-longman@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-cgroup.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index b36ba1d40ba1d..96af8224992e6 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -323,6 +323,7 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk, blkg->q = disk->queue; INIT_LIST_HEAD(&blkg->q_node); blkg->blkcg = blkcg; + blkg->iostat.blkg = blkg; #ifdef CONFIG_BLK_CGROUP_PUNT_BIO spin_lock_init(&blkg->async_bio_lock); bio_list_init(&blkg->async_bios); @@ -1047,6 +1048,8 @@ static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu) smp_mb();
WRITE_ONCE(bisc->lqueued, false); + if (bisc == &blkg->iostat) + goto propagate_up; /* propagate up to parent only */
/* fetch the current per-cpu values */ do { @@ -1056,10 +1059,24 @@ static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu)
blkcg_iostat_update(blkg, &cur, &bisc->last);
+propagate_up: /* propagate global delta to parent (unless that's root) */ - if (parent && parent->parent) + if (parent && parent->parent) { blkcg_iostat_update(parent, &blkg->iostat.cur, &blkg->iostat.last); + /* + * Queue parent->iostat to its blkcg's lockless + * list to propagate up to the grandparent if the + * iostat hasn't been queued yet. + */ + if (!parent->iostat.lqueued) { + struct llist_head *plhead; + + plhead = per_cpu_ptr(parent->blkcg->lhead, cpu); + llist_add(&parent->iostat.lnode, plhead); + parent->iostat.lqueued = true; + } + } } raw_spin_unlock_irqrestore(&blkg_stat_lock, flags); out: