======================================================
[ INFO: possible circular locking dependency detected ]
4.4.155+ #34 Not tainted
-------------------------------------------------------
syz-executor4/12445 is trying to acquire lock:
 (&bdev->bd_mutex){+.+.+.}, at: [  227.818325] audit_printk_skb: 90 callbacks suppressed
audit: type=1400 audit(1536643880.907:418): avc:  denied  { create } for  pid=12452 comm="syz-executor1" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1
audit: type=1400 audit(1536643880.907:419): avc:  denied  { write } for  pid=12452 comm="syz-executor1" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1
audit: type=1400 audit(1536643880.917:420): avc:  denied  { read } for  pid=12452 comm="syz-executor1" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1
audit: type=1400 audit(1536643880.917:421): avc:  denied  { setattr } for  pid=12452 comm="syz-executor1" name="ns" dev="proc" ino=37055 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=dir permissive=1
[<ffffffff81a2250e>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189

but task is already holding lock:
 (&lo->lo_ctl_mutex#2){+.+...}, at: [<ffffffff81ce37d0>] lo_compat_ioctl+0x110/0x140 drivers/block/loop.c:1542

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff811fabee>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826864bb>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826864bb>] mutex_lock_nested+0xbb/0x840 kernel/locking/mutex.c:621
       [<ffffffff81ce3885>] __lo_release drivers/block/loop.c:1595 [inline]
       [<ffffffff81ce3885>] lo_release+0x85/0x1a0 drivers/block/loop.c:1618
       [<ffffffff81524816>] __blkdev_put+0x636/0x840 fs/block_dev.c:1535
       [<ffffffff81525895>] blkdev_put+0x85/0x560 fs/block_dev.c:1600
       [<ffffffff81525dfb>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1607
       [<ffffffff81478e25>] __fput+0x235/0x6f0 fs/file_table.c:208
       [<ffffffff81479365>] ____fput+0x15/0x20 fs/file_table.c:244
       [<ffffffff8112a6ef>] task_work_run+0x10f/0x190 kernel/task_work.c:115
       [<ffffffff81003edd>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
       [<ffffffff81003edd>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:253
       [<ffffffff810057a5>] prepare_exit_to_usermode arch/x86/entry/common.c:284 [inline]
       [<ffffffff810057a5>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:349
       [<ffffffff82690d6d>] int_ret_from_sys_call+0x25/0xa3

       [<ffffffff811fabee>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826864bb>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826864bb>] mutex_lock_nested+0xbb/0x840 kernel/locking/mutex.c:621
       [<ffffffff81cd972b>] lo_open+0x1b/0xa0 drivers/block/loop.c:1575
       [<ffffffff81524cce>] __blkdev_get+0x2ae/0xdf0 fs/block_dev.c:1213
       [<ffffffff8152799a>] blkdev_get+0x2da/0x920 fs/block_dev.c:1353
       [<ffffffff815281f5>] blkdev_open+0x1a5/0x250 fs/block_dev.c:1508
       [<ffffffff8146dc9d>] do_dentry_open+0x38d/0xbd0 fs/open.c:749
       [<ffffffff8147140a>] vfs_open+0x12a/0x210 fs/open.c:862
       [<ffffffff814a089c>] do_last fs/namei.c:3222 [inline]
       [<ffffffff814a089c>] path_openat+0x50c/0x39a0 fs/namei.c:3359
       [<ffffffff814a79c7>] do_filp_open+0x197/0x270 fs/namei.c:3393
       [<ffffffff81471d2c>] do_sys_open+0x31c/0x610 fs/open.c:1038
       [<ffffffff8147204d>] SYSC_open fs/open.c:1056 [inline]
       [<ffffffff8147204d>] SyS_open+0x2d/0x40 fs/open.c:1051
       [<ffffffff82690be1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff811f729e>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff811f729e>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff811f729e>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff811f729e>] __lock_acquire+0x3b6e/0x5ba0 kernel/locking/lockdep.c:3213
       [<ffffffff811fabee>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826864bb>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826864bb>] mutex_lock_nested+0xbb/0x840 kernel/locking/mutex.c:621
       [<ffffffff81a2250e>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
       [<ffffffff81cdad5c>] loop_reread_partitions+0x7c/0x90 drivers/block/loop.c:648
       [<ffffffff81cdb7ee>] loop_set_status+0xa7e/0xfe0 drivers/block/loop.c:1191
       [<ffffffff81cdbdea>] loop_set_status_compat+0x9a/0xf0 drivers/block/loop.c:1515
       [<ffffffff81ce37db>] lo_compat_ioctl+0x11b/0x140 drivers/block/loop.c:1543
       [<ffffffff81a4ed64>] compat_blkdev_ioctl+0x3a4/0x37eb block/compat_ioctl.c:751
       [<ffffffff8156db7e>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
       [<ffffffff8156db7e>] compat_SyS_ioctl+0x62e/0x22a0 fs/compat_ioctl.c:1544
       [<ffffffff81005ffe>] do_syscall_32_irqs_on arch/x86/entry/common.c:393 [inline]
       [<ffffffff81005ffe>] do_fast_syscall_32+0x31e/0x8b0 arch/x86/entry/common.c:460
       [<ffffffff82692350>] sysenter_flags_fixed+0xd/0x1a

other info that might help us debug this:

Chain exists of:
 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz-executor4/12445:
 #0:  (&lo->lo_ctl_mutex#2){+.+...}, at: [<ffffffff81ce37d0>] lo_compat_ioctl+0x110/0x140 drivers/block/loop.c:1542

stack backtrace:
CPU: 1 PID: 12445 Comm: syz-executor4 Not tainted 4.4.155+ #34
 0000000000000000 da839d2943cbc276 ffff8801c254f5f8 ffffffff81a556dd
 ffffffff83a976a0 ffffffff83abc6f0 ffffffff83a96ad0 ffff8801d12ea0a8
 ffff8801d12e97c0 ffff8801c254f640 ffffffff8139240f 0000000000000001
Call Trace:
 [<ffffffff81a556dd>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81a556dd>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8139240f>] print_circular_bug.cold.34+0x2f7/0x432 kernel/locking/lockdep.c:1226
 [<ffffffff811f729e>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff811f729e>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff811f729e>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff811f729e>] __lock_acquire+0x3b6e/0x5ba0 kernel/locking/lockdep.c:3213
 [<ffffffff811fabee>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff826864bb>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff826864bb>] mutex_lock_nested+0xbb/0x840 kernel/locking/mutex.c:621
 [<ffffffff81a2250e>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
 [<ffffffff81cdad5c>] loop_reread_partitions+0x7c/0x90 drivers/block/loop.c:648
 [<ffffffff81cdb7ee>] loop_set_status+0xa7e/0xfe0 drivers/block/loop.c:1191
 [<ffffffff81cdbdea>] loop_set_status_compat+0x9a/0xf0 drivers/block/loop.c:1515
 [<ffffffff81ce37db>] lo_compat_ioctl+0x11b/0x140 drivers/block/loop.c:1543
 [<ffffffff81a4ed64>] compat_blkdev_ioctl+0x3a4/0x37eb block/compat_ioctl.c:751
 [<ffffffff8156db7e>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff8156db7e>] compat_SyS_ioctl+0x62e/0x22a0 fs/compat_ioctl.c:1544
 [<ffffffff81005ffe>] do_syscall_32_irqs_on arch/x86/entry/common.c:393 [inline]
 [<ffffffff81005ffe>] do_fast_syscall_32+0x31e/0x8b0 arch/x86/entry/common.c:460
 [<ffffffff82692350>] sysenter_flags_fixed+0xd/0x1a
loop_reread_partitions: partition scan of loop0 (ö8Ý‚p'ÅfÖ{I®7Ñ@óS	¹Ê,bÕ~ÏíXÛøq2/.h/Jýü
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qtaguid: iface_stat: iface_check_stats_reset_and_adjust(lo): iface reset its stats unexpectedly
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