Message-ID: <001a11446e86e97ceb055cf07f4e@google.com>
Date:   Wed, 01 Nov 2017 12:01:31 -0700
From:   syzbot 
        <bot+4684a000d5abdade83fac55b1e7d1f935ef1936e@...kaller.appspotmail.com>
To:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: possible deadlock in blkdev_reread_part

Hello,

syzkaller hit the following crash on  
e19b205be43d11bff638cad4487008c48d21c103
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


======================================================
WARNING: possible circular locking dependency detected
4.14.0-rc2+ #10 Not tainted
------------------------------------------------------
syzkaller821047/2981 is trying to acquire lock:
  (&bdev->bd_mutex){+.+.}, at: [<ffffffff8232c60e>]  
blkdev_reread_part+0x1e/0x40 block/ioctl.c:192

but task is already holding lock:
  (&lo->lo_ctl_mutex#2){+.+.}, at: [<ffffffff83541ef9>]  
lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1533

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&lo->lo_ctl_mutex#2){+.+.}:
        check_prevs_add kernel/locking/lockdep.c:2020 [inline]
        validate_chain kernel/locking/lockdep.c:2469 [inline]
        __lock_acquire+0x328f/0x4620 kernel/locking/lockdep.c:3498
        lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
        __mutex_lock_common kernel/locking/mutex.c:756 [inline]
        __mutex_lock+0x16f/0x19d0 kernel/locking/mutex.c:893
        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
        lo_release+0x6b/0x180 drivers/block/loop.c:1587
        __blkdev_put+0x602/0x7c0 fs/block_dev.c:1780
        blkdev_put+0x85/0x4f0 fs/block_dev.c:1845
        blkdev_close+0x91/0xc0 fs/block_dev.c:1852
        __fput+0x333/0x7f0 fs/file_table.c:210
        ____fput+0x15/0x20 fs/file_table.c:244
        task_work_run+0x199/0x270 kernel/task_work.c:112
        tracehook_notify_resume include/linux/tracehook.h:191 [inline]
        exit_to_usermode_loop+0x296/0x310 arch/x86/entry/common.c:162
        prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
        syscall_return_slowpath+0x42f/0x510 arch/x86/entry/common.c:266
        entry_SYSCALL_64_fastpath+0xbc/0xbe

-> #0 (&bdev->bd_mutex){+.+.}:
        check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894
        check_prevs_add kernel/locking/lockdep.c:2020 [inline]
        validate_chain kernel/locking/lockdep.c:2469 [inline]
        __lock_acquire+0x328f/0x4620 kernel/locking/lockdep.c:3498
        lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
        __mutex_lock_common kernel/locking/mutex.c:756 [inline]
        __mutex_lock+0x16f/0x19d0 kernel/locking/mutex.c:893
        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
        blkdev_reread_part+0x1e/0x40 block/ioctl.c:192
        loop_reread_partitions+0x12f/0x1a0 drivers/block/loop.c:614
        loop_set_status+0x9ba/0xf60 drivers/block/loop.c:1156
        loop_set_status_compat+0x92/0xf0 drivers/block/loop.c:1506
        lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1534
        compat_blkdev_ioctl+0x3ba/0x1850 block/compat_ioctl.c:405
        C_SYSC_ioctl fs/compat_ioctl.c:1593 [inline]
        compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1540
        do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline]
        do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391
        entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124

other info that might help us debug this:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&lo->lo_ctl_mutex#2);
                                lock(&bdev->bd_mutex);
                                lock(&lo->lo_ctl_mutex#2);
   lock(&bdev->bd_mutex);

  *** DEADLOCK ***

1 lock held by syzkaller821047/2981:
  #0:  (&lo->lo_ctl_mutex#2){+.+.}, at: [<ffffffff83541ef9>]  
lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1533

stack backtrace:
CPU: 0 PID: 2981 Comm: syzkaller821047 Not tainted 4.14.0-rc2+ #10
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:16 [inline]
  dump_stack+0x194/0x257 lib/dump_stack.c:52
  print_circular_bug+0x503/0x710 kernel/locking/lockdep.c:1259
  check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894
  check_prevs_add kernel/locking/lockdep.c:2020 [inline]
  validate_chain kernel/locking/lockdep.c:2469 [inline]
  __lock_acquire+0x328f/0x4620 kernel/locking/lockdep.c:3498
  lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
  __mutex_lock_common kernel/locking/mutex.c:756 [inline]
  __mutex_lock+0x16f/0x19d0 kernel/locking/mutex.c:893
  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
  blkdev_reread_part+0x1e/0x40 block/ioctl.c:192
  loop_reread_partitions+0x12f/0x1a0 drivers/block/loop.c:614
  loop_set_status+0x9ba/0xf60 drivers/block/loop.c:1156
  loop_set_status_compat+0x92/0xf0 drivers/block/loop.c:1506
  lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1534
  compat_blkdev_ioctl+0x3ba/0x1850 block/compat_ioctl.c:405
  C_SYSC_ioctl fs/compat_ioctl.c:1593 [inline]
  compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1540
  do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline]
  do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391
  entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124
RIP: 0023:0xf7f4bc79
RSP: 002b:00000000ff90868c EFLAGS: 00000286 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000004c02
RDX: 00000


---
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