btrfs triggered lockdep WARN.

[Dave Jones]

Another bug caused by this script. https://github.com/kernelslacker/io-tests/blob/master/setup.sh

WARNING: at kernel/lockdep.c:708 __lock_acquire+0x183b/0x1b70()
Modules linked in: sctp lec bridge 8021q garp stp mrp fuse dlci tun bnep hidp rfcomm l2tp_ppp l2tp_netlink l2tp_core vmw_vsock_vmci_transport vmw_vmci vsock cmtp kernelcapi nfnetlink ipt_ULOG scsi_transport_iscsi rose phonet rds irda nfc ipx p8023 p8022 netrom af_key can_raw ax25 llc2 af_802154 x25 pppoe caif_socket pppox can_bcm caif ppp_generic slhc crc_ccitt atm appletalk af_rxrpc psnap llc can btrfs kvm_amd kvm snd_hda_codec_realtek snd_hda_intel btusb snd_hda_codec xor bluetooth raid6_pq serio_raw snd_pcm microcode pcspkr libcrc32c zlib_deflate snd_page_alloc snd_timer snd rfkill edac_core soundcore r8169 mii sr_mod cdrom pata_atiixp radeon backlight drm_kms_helper ttm
CPU: 3 PID: 2340684 Comm: rm Not tainted 3.10.0-rc7+ #8 
Hardware name: Gigabyte Technology Co., Ltd. GA-MA78GM-S2H/GA-MA78GM-S2H, BIOS F12a 04/23/2010
 ffffffff819fb83b ffff88010a751aa0 ffffffff816aed7b ffff88010a751ad8
 ffffffff810432b0 0000000000000002 ffffffff8253e3d0 ffff88002e1a9810
 00017ee5aac67d60 0000000000000000 ffff88010a751ae8 ffffffff8104339a
Call Trace:
 [<ffffffff816aed7b>] dump_stack+0x19/0x1b
 [<ffffffff810432b0>] warn_slowpath_common+0x70/0xa0
 [<ffffffff8104339a>] warn_slowpath_null+0x1a/0x20
 [<ffffffff810ba40b>] __lock_acquire+0x183b/0x1b70
 [<ffffffff81333bd0>] ? delay_tsc+0x90/0xe0
 [<ffffffff810baee3>] lock_acquire+0x93/0x1e0
 [<ffffffffa040f937>] ? btrfs_try_tree_write_lock+0x47/0xc0 [btrfs]
 [<ffffffff816b6c11>] _raw_write_lock+0x41/0x80
 [<ffffffffa040f937>] ? btrfs_try_tree_write_lock+0x47/0xc0 [btrfs]
 [<ffffffffa040f937>] btrfs_try_tree_write_lock+0x47/0xc0 [btrfs]
 [<ffffffffa03b4bad>] btrfs_search_slot+0x80d/0x950 [btrfs]
 [<ffffffffa03cd3a6>] btrfs_del_inode_ref+0x76/0x3b0 [btrfs]
 [<ffffffffa03f3469>] ? release_extent_buffer+0xb9/0xe0 [btrfs]
 [<ffffffffa03f9aaf>] ? free_extent_buffer+0x4f/0xa0 [btrfs]
 [<ffffffffa03e0091>] __btrfs_unlink_inode+0x181/0x390 [btrfs]
 [<ffffffffa03e2e17>] btrfs_unlink_inode+0x27/0x50 [btrfs]
 [<ffffffffa03e2ead>] btrfs_unlink+0x6d/0xc0 [btrfs]
 [<ffffffff811bfb60>] vfs_unlink+0xa0/0x110
 [<ffffffff811bfd47>] do_unlinkat+0x177/0x230
 [<ffffffff810b8815>] ? trace_hardirqs_on_caller+0x115/0x1e0
 [<ffffffff810b88ed>] ? trace_hardirqs_on+0xd/0x10
 [<ffffffff8100f525>] ? syscall_trace_enter+0x25/0x290
 [<ffffffff811c274b>] SyS_unlinkat+0x1b/0x40
 [<ffffffff816bf394>] tracesys+0xdd/0xe2
---[ end trace 9d90045eda25c268 ]---

That WARN is..

 704                         /*
 705                          * Huh! same key, different name? Did someone trample
 706                          * on some memory? We're most confused.
 707                          */
 708                         WARN_ON_ONCE(class->name != lock->name);


Most confusing indeed.

	Dave

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