======================================================
[ INFO: possible circular locking dependency detected ]
4.4.174+ #17 Not tainted
-------------------------------------------------------
syz-executor.3/15636 is trying to acquire lock:
 (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff815e4cc2>] do_io_accounting+0x1f2/0x7f0 fs/proc/base.c:2666

but task is already holding lock:
 (&p->lock){+.+.+.}, at: [<ffffffff81507c66>] seq_read+0xd6/0x1240 fs/seq_file.c:178

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270c191>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270c191>] mutex_lock_nested+0xc1/0xb80 kernel/locking/mutex.c:621
       [<ffffffff81507c66>] seq_read+0xd6/0x1240 fs/seq_file.c:178
       [<ffffffff81497088>] do_loop_readv_writev+0x148/0x1e0 fs/read_write.c:682
       [<ffffffff81498ee3>] do_readv_writev+0x573/0x6e0 fs/read_write.c:812
       [<ffffffff814990ca>] vfs_readv+0x7a/0xb0 fs/read_write.c:836
       [<ffffffff8153601c>] kernel_readv fs/splice.c:586 [inline]
       [<ffffffff8153601c>] default_file_splice_read+0x3ac/0x8b0 fs/splice.c:662
       [<ffffffff815321ff>] do_splice_to+0xff/0x160 fs/splice.c:1154
       [<ffffffff815324a9>] splice_direct_to_actor+0x249/0x850 fs/splice.c:1226
       [<ffffffff81532c55>] do_splice_direct+0x1a5/0x260 fs/splice.c:1337
       [<ffffffff8149a2fd>] do_sendfile+0x4ed/0xba0 fs/read_write.c:1229
       [<ffffffff8149c474>] C_SYSC_sendfile fs/read_write.c:1311 [inline]
       [<ffffffff8149c474>] compat_SyS_sendfile+0x144/0x160 fs/read_write.c:1294
       [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
       [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
       [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8149ea2f>] percpu_down_read include/linux/percpu-rwsem.h:26 [inline]
       [<ffffffff8149ea2f>] __sb_start_write+0x1af/0x310 fs/super.c:1239
       [<ffffffff816c3af4>] sb_start_write include/linux/fs.h:1517 [inline]
       [<ffffffff816c3af4>] ext4_run_li_request fs/ext4/super.c:2685 [inline]
       [<ffffffff816c3af4>] ext4_lazyinit_thread fs/ext4/super.c:2784 [inline]
       [<ffffffff816c3af4>] ext4_lazyinit_thread+0x1e4/0x7b0 fs/ext4/super.c:2760
       [<ffffffff811342c3>] kthread+0x273/0x310 kernel/kthread.c:211
       [<ffffffff82718fc5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:537

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270c191>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270c191>] mutex_lock_nested+0xc1/0xb80 kernel/locking/mutex.c:621
       [<ffffffff816cdacd>] ext4_register_li_request+0x2fd/0x7d0 fs/ext4/super.c:2972
       [<ffffffff816cf306>] ext4_remount+0x1366/0x1b90 fs/ext4/super.c:4922
       [<ffffffff814a1ccb>] do_remount_sb2+0x41b/0x7a0 fs/super.c:781
       [<ffffffff815028ab>] do_remount fs/namespace.c:2347 [inline]
       [<ffffffff815028ab>] do_mount+0xfdb/0x2a40 fs/namespace.c:2860
       [<ffffffff81504d00>] SYSC_mount fs/namespace.c:3063 [inline]
       [<ffffffff81504d00>] SyS_mount+0x130/0x1d0 fs/namespace.c:3041
       [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270c191>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270c191>] mutex_lock_nested+0xc1/0xb80 kernel/locking/mutex.c:621
       [<ffffffff816cd859>] ext4_register_li_request+0x89/0x7d0 fs/ext4/super.c:2945
       [<ffffffff816cf306>] ext4_remount+0x1366/0x1b90 fs/ext4/super.c:4922
       [<ffffffff814a1ccb>] do_remount_sb2+0x41b/0x7a0 fs/super.c:781
       [<ffffffff815028ab>] do_remount fs/namespace.c:2347 [inline]
       [<ffffffff815028ab>] do_mount+0xfdb/0x2a40 fs/namespace.c:2860
       [<ffffffff81504d00>] SYSC_mount fs/namespace.c:3063 [inline]
       [<ffffffff81504d00>] SyS_mount+0x130/0x1d0 fs/namespace.c:3041
       [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff827139a2>] down_read+0x42/0x60 kernel/locking/rwsem.c:22
       [<ffffffff814a1411>] iterate_supers+0xe1/0x250 fs/super.c:547
       [<ffffffff819b19f7>] selinux_complete_init+0x2f/0x31 security/selinux/hooks.c:6154
       [<ffffffff819a353d>] security_load_policy+0x69d/0x9c0 security/selinux/ss/services.c:2060
       [<ffffffff81979e55>] sel_write_load+0x175/0xf90 security/selinux/selinuxfs.c:535
       [<ffffffff81496916>] __vfs_write+0x116/0x3d0 fs/read_write.c:491
       [<ffffffff81498612>] vfs_write+0x182/0x4e0 fs/read_write.c:540
       [<ffffffff8149ac4c>] SYSC_write fs/read_write.c:587 [inline]
       [<ffffffff8149ac4c>] SyS_write+0xdc/0x1c0 fs/read_write.c:579
       [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270c191>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270c191>] mutex_lock_nested+0xc1/0xb80 kernel/locking/mutex.c:621
       [<ffffffff81977a39>] sel_commit_bools_write+0x89/0x260 security/selinux/selinuxfs.c:1142
       [<ffffffff81496916>] __vfs_write+0x116/0x3d0 fs/read_write.c:491
       [<ffffffff81496ce2>] __kernel_write+0x112/0x370 fs/read_write.c:513
       [<ffffffff81532e6d>] write_pipe_buf+0x15d/0x1f0 fs/splice.c:1074
       [<ffffffff81533b6e>] splice_from_pipe_feed fs/splice.c:776 [inline]
       [<ffffffff81533b6e>] __splice_from_pipe+0x37e/0x7a0 fs/splice.c:901
       [<ffffffff81536be8>] splice_from_pipe+0x108/0x170 fs/splice.c:936
       [<ffffffff81536cdc>] default_file_splice_write+0x3c/0x80 fs/splice.c:1086
       [<ffffffff81537d31>] do_splice_from fs/splice.c:1128 [inline]
       [<ffffffff81537d31>] do_splice fs/splice.c:1404 [inline]
       [<ffffffff81537d31>] SYSC_splice fs/splice.c:1707 [inline]
       [<ffffffff81537d31>] SyS_splice+0xd71/0x13a0 fs/splice.c:1690
       [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
       [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
       [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270c191>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270c191>] mutex_lock_nested+0xc1/0xb80 kernel/locking/mutex.c:621
       [<ffffffff814b28fd>] __pipe_lock fs/pipe.c:86 [inline]
       [<ffffffff814b28fd>] fifo_open+0x15d/0xa00 fs/pipe.c:896
       [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
       [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
       [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
       [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
       [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
       [<ffffffff814a7c8c>] do_open_execat+0x10c/0x6e0 fs/exec.c:805
       [<ffffffff814ad306>] do_execveat_common.isra.0+0x6f6/0x1e90 fs/exec.c:1577
       [<ffffffff814af4e8>] compat_do_execve fs/exec.c:1710 [inline]
       [<ffffffff814af4e8>] C_SYSC_execve fs/exec.c:1785 [inline]
       [<ffffffff814af4e8>] compat_SyS_execve+0x48/0x60 fs/exec.c:1781
       [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
       [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
       [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a

       [<ffffffff81202d86>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff81202d86>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff81202d86>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff81202d86>] __lock_acquire+0x37d6/0x4f50 kernel/locking/lockdep.c:3213
       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270d8a2>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270d8a2>] mutex_lock_killable_nested+0xd2/0xd00 kernel/locking/mutex.c:641
       [<ffffffff815e4cc2>] do_io_accounting+0x1f2/0x7f0 fs/proc/base.c:2666
       [<ffffffff815e5310>] proc_tid_io_accounting+0x20/0x30 fs/proc/base.c:2709
       [<ffffffff815e2e66>] proc_single_show+0xf6/0x160 fs/proc/base.c:805
       [<ffffffff8150805d>] seq_read+0x4cd/0x1240 fs/seq_file.c:240
       [<ffffffff81496556>] __vfs_read+0x116/0x3c0 fs/read_write.c:434
       [<ffffffff81498264>] vfs_read+0x134/0x360 fs/read_write.c:456
       [<ffffffff8149aa8c>] SYSC_read fs/read_write.c:571 [inline]
       [<ffffffff8149aa8c>] SyS_read+0xdc/0x1c0 fs/read_write.c:564
       [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
       [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
       [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a

other info that might help us debug this:

Chain exists of:
 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&p->lock);
                               lock(sb_writers#4);
                               lock(&p->lock);
  lock(&sig->cred_guard_mutex);

 *** DEADLOCK ***

2 locks held by syz-executor.3/15636:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff814f4378>] __fdget_pos+0xa8/0xd0 fs/file.c:780
 #1:  (&p->lock){+.+.+.}, at: [<ffffffff81507c66>] seq_read+0xd6/0x1240 fs/seq_file.c:178

stack backtrace:
CPU: 0 PID: 15636 Comm: syz-executor.3 Not tainted 4.4.174+ #17
 0000000000000000 6e3411d939a95dee ffff8801d230f660 ffffffff81aad1a1
 ffffffff84057a80 ffff8801d8d0df00 ffffffff83ab6860 ffffffff83ab81b0
 ffffffff83abc380 ffff8801d230f6b0 ffffffff813abcda ffffffff83e1f380
Call Trace:
 [<ffffffff81aad1a1>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81aad1a1>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<ffffffff813abcda>] print_circular_bug.cold+0x2f7/0x44e kernel/locking/lockdep.c:1226
 [<ffffffff81202d86>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff81202d86>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff81202d86>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff81202d86>] __lock_acquire+0x37d6/0x4f50 kernel/locking/lockdep.c:3213
 [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff8270d8a2>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff8270d8a2>] mutex_lock_killable_nested+0xd2/0xd00 kernel/locking/mutex.c:641
 [<ffffffff815e4cc2>] do_io_accounting+0x1f2/0x7f0 fs/proc/base.c:2666
 [<ffffffff815e5310>] proc_tid_io_accounting+0x20/0x30 fs/proc/base.c:2709
 [<ffffffff815e2e66>] proc_single_show+0xf6/0x160 fs/proc/base.c:805
 [<ffffffff8150805d>] seq_read+0x4cd/0x1240 fs/seq_file.c:240
 [<ffffffff81496556>] __vfs_read+0x116/0x3c0 fs/read_write.c:434
 [<ffffffff81498264>] vfs_read+0x134/0x360 fs/read_write.c:456
 [<ffffffff8149aa8c>] SYSC_read fs/read_write.c:571 [inline]
 [<ffffffff8149aa8c>] SyS_read+0xdc/0x1c0 fs/read_write.c:564
 [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
 [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a
audit: type=1400 audit(1570590794.429:474): avc:  denied  { create } for  pid=15614 comm="syz-executor.5" 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=0
audit: type=1400 audit(1570590794.519:475): avc:  denied  { create } for  pid=15633 comm="syz-executor.0" 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=0
audit: type=1400 audit(1570590795.329:476): avc:  denied  { create } for  pid=15672 comm="syz-executor.0" 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=0