From: Ming Lei <ming.lei@redhat.com>
Date: Tue, 1 Sep 2020 18:07:38 +0800
Subject: [PATCH] block: release disk reference in hd_struct_free_work
Git-commit: cafe01ef8fcb248583038e1be071383530fe355a
Patch-mainline: v5.9-rc4
References: bsc#1175995,jsc#SLE-15608

Commit e8c7d14ac6c3 ("block: revert back to synchronous request_queue removal")
stops to release request queue from wq context because that commit
supposed all blk_put_queue() is called in context which is allowed
to sleep. However, this assumption isn't true because we release disk's
reference in partition's percpu_ref's ->release() which doesn't allow
to sleep, because the ->release() is run via call_rcu().

Fixes this issue by moving put disk reference into hd_struct_free_work()

Fixes: e8c7d14ac6c3 ("block: revert back to synchronous request_queue removal")
Reported-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 block/partitions/core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/block/partitions/core.c b/block/partitions/core.c
index e62a98a8eeb7..5a18c8edabbc 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -278,6 +278,15 @@ static void hd_struct_free_work(struct work_struct *work)
 {
 	struct hd_struct *part =
 		container_of(to_rcu_work(work), struct hd_struct, rcu_work);
+	struct gendisk *disk = part_to_disk(part);
+
+	/*
+	 * Release the disk reference acquired in delete_partition here.
+	 * We can't release it in hd_struct_free because the final put_device
+	 * needs process context and thus can't be run directly from a
+	 * percpu_ref ->release handler.
+	 */
+	put_device(disk_to_dev(disk));
 
 	part->start_sect = 0;
 	part->nr_sects = 0;
@@ -293,7 +302,6 @@ static void hd_struct_free(struct percpu_ref *ref)
 		rcu_dereference_protected(disk->part_tbl, 1);
 
 	rcu_assign_pointer(ptbl->last_lookup, NULL);
-	put_device(disk_to_dev(disk));
 
 	INIT_RCU_WORK(&part->rcu_work, hd_struct_free_work);
 	queue_rcu_work(system_wq, &part->rcu_work);
-- 
2.16.4