block: Skip destroyed blkg when restart in blkg_destroy_all()

Kernel hang in blkg_destroy_all() when total blkg greater than
BLKG_DESTROY_BATCH_SIZE, because of not removing destroyed blkg in
blkg_list. So the size of blkg_list is same after destroying a
batch of blkg, and the infinite 'restart' occurs.

Since blkg should stay on the queue list until blkg_free_workfn(),
skip destroyed blkg when restart a new round, which will solve this
kernel hang issue and satisfy the previous will to restart.

Reported-by: Xiangfei Ma <xiangfeix.ma@intel.com>
Tested-by: Xiangfei Ma <xiangfeix.ma@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Signed-off-by: Tao Su <tao1.su@linux.intel.com>
Fixes: f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()")
Suggested-and-reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20230428045149.1310073-1-tao1.su@linux.intel.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 1c1ebeb..0ecb4cc 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -527,6 +527,9 @@ restart:
        list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
                struct blkcg *blkcg = blkg->blkcg;
 
+               if (hlist_unhashed(&blkg->blkcg_node))
+                       continue;
+
                spin_lock(&blkcg->lock);
                blkg_destroy(blkg);
                spin_unlock(&blkcg->lock);