WARNING: bad unlock balance in ucma_event_handler

[syzbot <syzbot+e5579222b6a3edd96522@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    73fcb1a370c7 Merge branch 'akpm' (patches from Andrew)
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16d70827800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f3b4e30da84ec1ed
dashboard link: https://syzkaller.appspot.com/bug?extid=e5579222b6a3edd96522
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=176daf97800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15e7bd57800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e5579222b6a3edd96522@syzkaller.appspotmail.com


=====================================
WARNING: bad unlock balance detected!
4.17.0-rc5+ #58 Not tainted
-------------------------------------
kworker/u4:0/6 is trying to release lock (&file->mut) at:
[<ffffffff8593ecc0>] ucma_event_handler+0x780/0xff0  
drivers/infiniband/core/ucma.c:390
but there are no more locks to release!

other info that might help us debug this:
4 locks held by kworker/u4:0/6:
  #0:         (ptrval) ((wq_completion)"ib_addr"){+.+.}, at:  
__write_once_size include/linux/compiler.h:215 [inline]
  #0:         (ptrval) ((wq_completion)"ib_addr"){+.+.}, at:  
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
  #0:         (ptrval) ((wq_completion)"ib_addr"){+.+.}, at: atomic64_set  
include/asm-generic/atomic-instrumented.h:40 [inline]
  #0:         (ptrval) ((wq_completion)"ib_addr"){+.+.}, at: atomic_long_set  
include/asm-generic/atomic-long.h:57 [inline]
  #0:         (ptrval) ((wq_completion)"ib_addr"){+.+.}, at: set_work_data  
kernel/workqueue.c:617 [inline]
  #0:         (ptrval) ((wq_completion)"ib_addr"){+.+.}, at:  
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
  #0:         (ptrval) ((wq_completion)"ib_addr"){+.+.}, at:  
process_one_work+0xaef/0x1b50 kernel/workqueue.c:2116
  #1:         (ptrval) ((work_completion)(&(&req->work)->work)){+.+.}, at:  
process_one_work+0xb46/0x1b50 kernel/workqueue.c:2120
  #2:         (ptrval) (&id_priv->handler_mutex){+.+.}, at:  
addr_handler+0xa6/0x3d0 drivers/infiniband/core/cma.c:2796
  #3:         (ptrval) (&file->mut){+.+.}, at:  
ucma_event_handler+0x10e/0xff0 drivers/infiniband/core/ucma.c:350

stack backtrace:
CPU: 1 PID: 6 Comm: kworker/u4:0 Not tainted 4.17.0-rc5+ #58
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: ib_addr process_one_req
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
  print_unlock_imbalance_bug.cold.50+0xcc/0xd8 kernel/locking/lockdep.c:3484
  __lock_release kernel/locking/lockdep.c:3691 [inline]
  lock_release+0x77a/0xa10 kernel/locking/lockdep.c:3939
  __mutex_unlock_slowpath+0xeb/0x8a0 kernel/locking/mutex.c:1018
  mutex_unlock+0xd/0x10 kernel/locking/mutex.c:614
  ucma_event_handler+0x780/0xff0 drivers/infiniband/core/ucma.c:390
  addr_handler+0x2bd/0x3d0 drivers/infiniband/core/cma.c:2820
  process_one_req+0x2e8/0x750 drivers/infiniband/core/addr.c:616
  process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
  worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
  kthread+0x345/0x410 kernel/kthread.c:240
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412


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