btrfs: release path before iget_failed() in btrfs_read_locked_inode()

In the Linux kernel, the following vulnerability has been resolved:

btrfs: release path before iget_failed() in btrfs_read_locked_inode()

In btrfs_read_locked_inode() if we fail to lookup the inode, we jump to

the 'out' label with a path that has a read locked leaf and then we call

iget_failed(). This can result in a ABBA deadlock, since iget_failed()

triggers inode eviction and that causes the release of the delayed inode,

which must lock the delayed inode's mutex, and a task updating a delayed

inode starts by taking the node's mutex and then modifying the inode's

subvolume btree.

Syzbot reported the following lockdep splat for this:

======================================================

WARNING: possible circular locking dependency detected

syzkaller #0 Not tainted

------------------------------------------------------

btrfs-cleaner/8725 is trying to acquire lock:

ffff0000d6826a48 (&delayed_node->mutex){+.+.}-{4:4}, at: __btrfs_release_delayed_node+0xa0/0x9b0 fs/btrfs/delayed-inode.c:290

but task is already holding lock:

ffff0000dbeba878 (btrfs-tree-00){++++}-{4:4}, at: btrfs_tree_read_lock_nested+0x44/0x2ec fs/btrfs/locking.c:145

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (btrfs-tree-00){++++}-{4:4}:

__lock_release kernel/locking/lockdep.c:5574 [inline]

lock_release+0x198/0x39c kernel/locking/lockdep.c:5889

up_read+0x24/0x3c kernel/locking/rwsem.c:1632

btrfs_tree_read_unlock+0xdc/0x298 fs/btrfs/locking.c:169

btrfs_tree_unlock_rw fs/btrfs/locking.h:218 [inline]

btrfs_search_slot+0xa6c/0x223c fs/btrfs/ctree.c:2133

btrfs_lookup_inode+0xd8/0x38c fs/btrfs/inode-item.c:395

__btrfs_update_delayed_inode+0x124/0xed0 fs/btrfs/delayed-inode.c:1032

btrfs_update_delayed_inode fs/btrfs/delayed-inode.c:1118 [inline]

__btrfs_commit_inode_delayed_items+0x15f8/0x1748 fs/btrfs/delayed-inode.c:1141

__btrfs_run_delayed_items+0x1ac/0x514 fs/btrfs/delayed-inode.c:1176

btrfs_run_delayed_items_nr+0x28/0x38 fs/btrfs/delayed-inode.c:1219

flush_space+0x26c/0xb68 fs/btrfs/space-info.c:828

do_async_reclaim_metadata_space+0x110/0x364 fs/btrfs/space-info.c:1158

btrfs_async_reclaim_metadata_space+0x90/0xd8 fs/btrfs/space-info.c:1226

process_one_work+0x7e8/0x155c kernel/workqueue.c:3263

process_scheduled_works kernel/workqueue.c:3346 [inline]

worker_thread+0x958/0xed8 kernel/workqueue.c:3427

kthread+0x5fc/0x75c kernel/kthread.c:463

ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

-> #0 (&delayed_node->mutex){+.+.}-{4:4}:

check_prev_add kernel/locking/lockdep.c:3165 [inline]

check_prevs_add kernel/locking/lockdep.c:3284 [inline]

validate_chain kernel/locking/lockdep.c:3908 [inline]

__lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237

lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868

__mutex_lock_common+0x1d0/0x2678 kernel/locking/mutex.c:598

__mutex_lock kernel/locking/mutex.c:760 [inline]

mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812

__btrfs_release_delayed_node+0xa0/0x9b0 fs/btrfs/delayed-inode.c:290

btrfs_release_delayed_node fs/btrfs/delayed-inode.c:315 [inline]

btrfs_remove_delayed_node+0x68/0x84 fs/btrfs/delayed-inode.c:1326

btrfs_evict_inode+0x578/0xe28 fs/btrfs/inode.c:5587

evict+0x414/0x928 fs/inode.c:810

iput_final fs/inode.c:1914 [inline]

iput+0x95c/0xad4 fs/inode.c:1966

iget_failed+0xec/0x134 fs/bad_inode.c:248

btrfs_read_locked_inode+0xe1c/0x1234 fs/btrfs/inode.c:4101

btrfs_iget+0x1b0/0x264 fs/btrfs/inode.c:5837

btrfs_run_defrag_inode fs/btrfs/defrag.c:237 [inline]

btrfs_run_defrag_inodes+0x520/0xdc4 fs/btrf

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