block: Initialize bd_bdi on inode initialization
So far we initialized bd_bdi only in bdget(). That is fine for normal
bdev inodes however for the special case of the root inode of
blockdev_superblock that function is never called and thus bd_bdi is
left uninitialized. As a result bdev_evict_inode() may oops doing
bdi_put(root->bd_bdi) on that inode as can be seen when doing:
mount -t bdev none /mnt
Fix the problem by initializing bd_bdi when first allocating the inode
and then reinitializing bd_bdi in bdev_evict_inode().
Thanks to syzkaller team for finding the problem.
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Fixes: b1d2dc5659b4 ("block: Make blk_get_backing_dev_info() safe without open bdev")
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 77c30f1..2eca00e 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -870,6 +870,7 @@ static void init_once(void *foo)
#ifdef CONFIG_SYSFS
INIT_LIST_HEAD(&bdev->bd_holder_disks);
#endif
+ bdev->bd_bdi = &noop_backing_dev_info;
inode_init_once(&ei->vfs_inode);
/* Initialize mutex for freeze. */
mutex_init(&bdev->bd_fsfreeze_mutex);
@@ -884,8 +885,10 @@ static void bdev_evict_inode(struct inode *inode)
spin_lock(&bdev_lock);
list_del_init(&bdev->bd_list);
spin_unlock(&bdev_lock);
- if (bdev->bd_bdi != &noop_backing_dev_info)
+ if (bdev->bd_bdi != &noop_backing_dev_info) {
bdi_put(bdev->bd_bdi);
+ bdev->bd_bdi = &noop_backing_dev_info;
+ }
}
static const struct super_operations bdev_sops = {
@@ -988,7 +991,6 @@ struct block_device *bdget(dev_t dev)
bdev->bd_contains = NULL;
bdev->bd_super = NULL;
bdev->bd_inode = inode;
- bdev->bd_bdi = &noop_backing_dev_info;
bdev->bd_block_size = i_blocksize(inode);
bdev->bd_part_count = 0;
bdev->bd_invalidated = 0;
