Messages in this thread Patch in this message | | | From | Desmond Cheong Zhi Xi <> | Subject | [PATCH] mtd: fix lock hierarchy in deregister_mtd_blktrans | Date | Sat, 17 Jul 2021 18:07:19 +0800 |
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There is a lock hierarchy of major_names_lock --> mtd_table_mutex. One existing chain is as follows:
1. major_names_lock --> loop_ctl_mutex (when blk_request_module calls loop_probe)
2. loop_ctl_mutex --> bdev->bd_mutex (when loop_control_ioctl calls loop_remove, which then calls del_gendisk)
3. bdev->bd_mutex --> mtd_table_mutex (when blkdev_get_by_dev calls __blkdev_get, which then calls blktrans_open)
Since unregister_blkdev grabs the major_names_lock, we need to call it outside the critical section for mtd_table_mutex, otherwise we invert the lock hierarchy.
Reported-by: Hillf Danton <hdanton@sina.com> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> --- drivers/mtd/mtd_blkdevs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c index 7d26cfe24d05..87e26788ef60 100644 --- a/drivers/mtd/mtd_blkdevs.c +++ b/drivers/mtd/mtd_blkdevs.c @@ -563,8 +563,8 @@ int deregister_mtd_blktrans(struct mtd_blktrans_ops *tr) list_for_each_entry_safe(dev, next, &tr->devs, list) tr->remove_dev(dev); - unregister_blkdev(tr->major, tr->name); mutex_unlock(&mtd_table_mutex); + unregister_blkdev(tr->major, tr->name); BUG_ON(!list_empty(&tr->devs)); return 0; -- 2.25.1
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