[PATCH 2/3] block: let blkcg_gq grab request queue's refcnt

Ming Lei
2022-03-18T13:02:29Z

In the whole lifetime of blkcg_gq instance, ->q will be referred, such
as, ->pd_free_fn() is called in blkg_free, and throtl_pd_free() still
may touch the request queue via &tg->service_queue.pending_timer which
is handled by throtl_pending_timer_fn(), so it is reasonable to grab
request queue's refcnt by blkcg_gq instance.

Previously blkcg_exit_queue() is called from blk_release_queue, and it
is hard to avoid the use-after-free. But recently commit 1059699f87eb ("block:
move blkcg initialization/destroy into disk allocation/release handler")
is merged to for-5.18/block, it becomes simple to fix the issue by simply
grabbing request queue's refcnt.

Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-cgroup.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index fa063c6c0338..d53b0d69dd73 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -82,6 +82,8 @@ static void blkg_free(struct blkcg_gq *blkg)
if (blkg->pd[i])
blkcg_policy[i]->pd_free_fn(blkg->pd[i]);

+ if (blkg->q)
+ blk_put_queue(blkg->q);
free_percpu(blkg->iostat_cpu);
percpu_ref_exit(&blkg->refcnt);
kfree(blkg);
@@ -167,6 +169,9 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
if (!blkg->iostat_cpu)
goto err_free;

+ if (!blk_get_queue(q))
+ goto err_free;
+
blkg->q = q;
INIT_LIST_HEAD(&blkg->q_node);
spin_lock_init(&blkg->async_bio_lock);
--
2.31.1