fs: WARNING in locks_unlink_lock_ctx (not holding proper lock)

[Dmitry Vyukov]

Hello,

I am hitting lots of the following warnings while running syzkaller
fuzzer. Seems that path does not hold proper lock.

WARNING: CPU: 1 PID: 12090 at fs/locks.c:610 locks_unlink_lock_ctx+0x2c7/0x370
CPU: 1 PID: 12090 Comm: syz-executor Not tainted 4.8.0+ #28
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 ffff880038ba7728 ffffffff82d2b849 ffffffff00000016 fffffbfff10971e8
 ffffffff86e8c000 ffff880038ba7800 ffffffff86f42400 dffffc0000000000
 0000000000000009 ffff880038ba77f0 ffffffff816a229a 0000000041b58ab3
Call Trace:
 [<     inline     >] __dump_stack lib/dump_stack.c:15
 [<ffffffff82d2b849>] dump_stack+0x12e/0x185 lib/dump_stack.c:51
 [<ffffffff816a229a>] panic+0x1e9/0x3f4 kernel/panic.c:153
 [<ffffffff81354fb9>] __warn+0x1c9/0x1e0 kernel/panic.c:509
 [<ffffffff813551a1>] warn_slowpath_null+0x31/0x40 kernel/panic.c:552
 [<     inline     >] locks_delete_global_locks fs/locks.c:610
 [<ffffffff8193b247>] locks_unlink_lock_ctx+0x2c7/0x370 fs/locks.c:739
 [<ffffffff8193b30f>] locks_delete_lock_ctx+0x1f/0x80 fs/locks.c:751
 [<ffffffff8193d329>] lease_modify+0x229/0x2e0 fs/locks.c:1370
 [<     inline     >] locks_remove_lease fs/locks.c:2528
 [<ffffffff81947408>] locks_remove_file+0x2d8/0x380 fs/locks.c:2551
 [<ffffffff8182eea6>] __fput+0x1a6/0x780 fs/file_table.c:200
 [<ffffffff8182f50a>] ____fput+0x1a/0x20 fs/file_table.c:244
 [<ffffffff813bae68>] task_work_run+0xf8/0x170 kernel/task_work.c:116
 [<     inline     >] exit_task_work include/linux/task_work.h:21
 [<ffffffff81364de4>] do_exit+0x864/0x2ad0 kernel/exit.c:828
 [<ffffffff813671cd>] do_group_exit+0x10d/0x330 kernel/exit.c:931
 [<ffffffff8138a57f>] get_signal+0x62f/0x15e0 kernel/signal.c:2307
 [<ffffffff811cf344>] do_signal+0x84/0x18f0 arch/x86/kernel/signal.c:807
 [<ffffffff8100629b>] exit_to_usermode_loop+0x13b/0x200
arch/x86/entry/common.c:156
 [<     inline     >] prepare_exit_to_usermode arch/x86/entry/common.c:190
 [<     inline     >] syscall_return_slowpath arch/x86/entry/common.c:259
 [<ffffffff81008a4f>] do_syscall_64+0x49f/0x620 arch/x86/entry/common.c:285

On commit a6930aaee06755d1bdcfd943fbf614e4d92bb0c7 (Oct 5).