syzbot

======================================================
[ INFO: possible circular locking dependency detected ]
4.4.159+ #108 Not tainted
-------------------------------------------------------
syz-executor122/2096 is trying to acquire lock:
 (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff815e2cf4>] lock_trace+0x44/0xc0 fs/proc/base.c:448

but task is already holding lock:
 (&p->lock){+.+.+.}, at: [<ffffffff8150141d>] seq_read+0xdd/0x12b0 fs/seq_file.c:178

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fa74b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fa74b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff8150141d>] seq_read+0xdd/0x12b0 fs/seq_file.c:178
       [<ffffffff81491518>] do_loop_readv_writev+0x148/0x1e0 fs/read_write.c:680
       [<ffffffff81493351>] do_readv_writev+0x581/0x6f0 fs/read_write.c:810
       [<ffffffff81493538>] vfs_readv+0x78/0xb0 fs/read_write.c:834
       [<ffffffff8152f6df>] kernel_readv fs/splice.c:586 [inline]
       [<ffffffff8152f6df>] default_file_splice_read+0x50f/0x8f0 fs/splice.c:662
       [<ffffffff8152b5b7>] do_splice_to+0xf7/0x140 fs/splice.c:1154
       [<ffffffff8152b842>] splice_direct_to_actor+0x242/0x830 fs/splice.c:1226
       [<ffffffff8152bfd3>] do_splice_direct+0x1a3/0x270 fs/splice.c:1337
       [<ffffffff81494774>] do_sendfile+0x4e4/0xb80 fs/read_write.c:1227
       [<ffffffff81496763>] SYSC_sendfile64 fs/read_write.c:1282 [inline]
       [<ffffffff81496763>] SyS_sendfile64+0xc3/0x150 fs/read_write.c:1274
       [<ffffffff82705ca1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff81498e4e>] percpu_down_read include/linux/percpu-rwsem.h:26 [inline]
       [<ffffffff81498e4e>] __sb_start_write+0x1ae/0x310 fs/super.c:1221
       [<ffffffff816bb0f7>] sb_start_write include/linux/fs.h:1515 [inline]
       [<ffffffff816bb0f7>] ext4_run_li_request fs/ext4/super.c:2674 [inline]
       [<ffffffff816bb0f7>] ext4_lazyinit_thread+0x1a7/0x750 fs/ext4/super.c:2773
       [<ffffffff81134038>] kthread+0x268/0x300 kernel/kthread.c:211
       [<ffffffff82706085>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:510

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fa74b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fa74b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff816c51f4>] ext4_register_li_request+0x304/0x7a0 fs/ext4/super.c:2961
       [<ffffffff816c69f8>] ext4_remount+0x1368/0x1bb0 fs/ext4/super.c:4911
       [<ffffffff8149c0f8>] do_remount_sb2+0x428/0x7d0 fs/super.c:771
       [<ffffffff814fc03e>] do_remount fs/namespace.c:2335 [inline]
       [<ffffffff814fc03e>] do_mount+0x101e/0x2a10 fs/namespace.c:2848
       [<ffffffff814fe581>] SYSC_mount fs/namespace.c:3051 [inline]
       [<ffffffff814fe581>] SyS_mount+0x191/0x1c0 fs/namespace.c:3029
       [<ffffffff82705ca1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fa74b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fa74b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff816c4f77>] ext4_register_li_request+0x87/0x7a0 fs/ext4/super.c:2934
       [<ffffffff816c69f8>] ext4_remount+0x1368/0x1bb0 fs/ext4/super.c:4911
       [<ffffffff8149c0f8>] do_remount_sb2+0x428/0x7d0 fs/super.c:771
       [<ffffffff814fc03e>] do_remount fs/namespace.c:2335 [inline]
       [<ffffffff814fc03e>] do_mount+0x101e/0x2a10 fs/namespace.c:2848
       [<ffffffff814fe581>] SYSC_mount fs/namespace.c:3051 [inline]
       [<ffffffff814fe581>] SyS_mount+0x191/0x1c0 fs/namespace.c:3029
       [<ffffffff82705ca1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff82700cc2>] down_read+0x42/0x60 kernel/locking/rwsem.c:22
       [<ffffffff8149b811>] iterate_supers+0xe1/0x260 fs/super.c:537
       [<ffffffff8199e134>] selinux_complete_init+0x2f/0x31 security/selinux/hooks.c:6154
       [<ffffffff8198fd86>] security_load_policy+0x886/0x9b0 security/selinux/ss/services.c:2060
       [<ffffffff81965cb1>] sel_write_load+0x191/0xfc0 security/selinux/selinuxfs.c:535
       [<ffffffff81490dbc>] __vfs_write+0x11c/0x3e0 fs/read_write.c:489
       [<ffffffff81492a6e>] vfs_write+0x17e/0x4e0 fs/read_write.c:538
       [<ffffffff814950a9>] SYSC_write fs/read_write.c:585 [inline]
       [<ffffffff814950a9>] SyS_write+0xd9/0x1c0 fs/read_write.c:577
       [<ffffffff82705ca1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fa74b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fa74b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff81963797>] sel_commit_bools_write+0x87/0x250 security/selinux/selinuxfs.c:1142
       [<ffffffff81490dbc>] __vfs_write+0x11c/0x3e0 fs/read_write.c:489
       [<ffffffff8149118a>] __kernel_write+0x10a/0x350 fs/read_write.c:511
       [<ffffffff8152c1fd>] write_pipe_buf+0x15d/0x1f0 fs/splice.c:1074
       [<ffffffff8152d094>] splice_from_pipe_feed fs/splice.c:776 [inline]
       [<ffffffff8152d094>] __splice_from_pipe+0x364/0x790 fs/splice.c:901
       [<ffffffff81530159>] splice_from_pipe+0xf9/0x170 fs/splice.c:936
       [<ffffffff8153025c>] default_file_splice_write+0x3c/0x80 fs/splice.c:1086
       [<ffffffff81531321>] do_splice_from fs/splice.c:1128 [inline]
       [<ffffffff81531321>] do_splice fs/splice.c:1404 [inline]
       [<ffffffff81531321>] SYSC_splice fs/splice.c:1707 [inline]
       [<ffffffff81531321>] SyS_splice+0xde1/0x1430 fs/splice.c:1690
       [<ffffffff82705ca1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fa74b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fa74b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff814acbac>] __pipe_lock fs/pipe.c:86 [inline]
       [<ffffffff814acbac>] fifo_open+0x15c/0x9e0 fs/pipe.c:896
       [<ffffffff8148bbad>] do_dentry_open+0x38d/0xbd0 fs/open.c:749
       [<ffffffff8148f31a>] vfs_open+0x12a/0x210 fs/open.c:862
       [<ffffffff814beefc>] do_last fs/namei.c:3222 [inline]
       [<ffffffff814beefc>] path_openat+0x50c/0x39a0 fs/namei.c:3359
       [<ffffffff814c6027>] do_filp_open+0x197/0x270 fs/namei.c:3393
       [<ffffffff814a208f>] do_open_execat+0x10f/0x6f0 fs/exec.c:800
       [<ffffffff814a7641>] do_execveat_common.isra.14+0x6a1/0x1f00 fs/exec.c:1573
       [<ffffffff814a9812>] do_execve fs/exec.c:1679 [inline]
       [<ffffffff814a9812>] SYSC_execve fs/exec.c:1760 [inline]
       [<ffffffff814a9812>] SyS_execve+0x42/0x50 fs/exec.c:1755
       [<ffffffff82705fb5>] return_from_execve+0x0/0x23

       [<ffffffff811ff31c>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff811ff31c>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff811ff31c>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff811ff31c>] __lock_acquire+0x3e6c/0x5f10 kernel/locking/lockdep.c:3213
       [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff826fb8fc>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff826fb8fc>] mutex_lock_killable_nested+0xcc/0xa10 kernel/locking/mutex.c:641
       [<ffffffff815e2cf4>] lock_trace+0x44/0xc0 fs/proc/base.c:448
       [<ffffffff815e2fac>] proc_pid_personality+0x1c/0xc0 fs/proc/base.c:2835
       [<ffffffff815db19d>] proc_single_show+0xfd/0x170 fs/proc/base.c:791
       [<ffffffff815017f6>] seq_read+0x4b6/0x12b0 fs/seq_file.c:240
       [<ffffffff81491518>] do_loop_readv_writev+0x148/0x1e0 fs/read_write.c:680
       [<ffffffff81493351>] do_readv_writev+0x581/0x6f0 fs/read_write.c:810
       [<ffffffff81493538>] vfs_readv+0x78/0xb0 fs/read_write.c:834
       [<ffffffff8152f6df>] kernel_readv fs/splice.c:586 [inline]
       [<ffffffff8152f6df>] default_file_splice_read+0x50f/0x8f0 fs/splice.c:662
       [<ffffffff8152b5b7>] do_splice_to+0xf7/0x140 fs/splice.c:1154
       [<ffffffff8152b842>] splice_direct_to_actor+0x242/0x830 fs/splice.c:1226
       [<ffffffff8152bfd3>] do_splice_direct+0x1a3/0x270 fs/splice.c:1337
       [<ffffffff81494774>] do_sendfile+0x4e4/0xb80 fs/read_write.c:1227
       [<ffffffff81496763>] SYSC_sendfile64 fs/read_write.c:1282 [inline]
       [<ffffffff81496763>] SyS_sendfile64+0xc3/0x150 fs/read_write.c:1274
       [<ffffffff82705ca1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

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 ***

1 lock held by syz-executor122/2096:
 #0:  (&p->lock){+.+.+.}, at: [<ffffffff8150141d>] seq_read+0xdd/0x12b0 fs/seq_file.c:178

stack backtrace:
CPU: 1 PID: 2096 Comm: syz-executor122 Not tainted 4.4.159+ #108
 0000000000000000 6addc59d46797ecf ffff8800b6666f28 ffffffff81a994bd
 ffffffff83ab46a0 ffffffff83ab04d0 ffffffff83aaeb80 ffff8801d54467e8
 ffff8801d5445f00 ffff8800b6666f70 ffffffff813a84ea 0000000000000001
Call Trace:
 [<ffffffff81a994bd>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81a994bd>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff813a84ea>] print_circular_bug.cold.34+0x2f7/0x432 kernel/locking/lockdep.c:1226
 [<ffffffff811ff31c>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff811ff31c>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff811ff31c>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff811ff31c>] __lock_acquire+0x3e6c/0x5f10 kernel/locking/lockdep.c:3213
 [<ffffffff81202efe>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff826fb8fc>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff826fb8fc>] mutex_lock_killable_nested+0xcc/0xa10 kernel/locking/mutex.c:641
 [<ffffffff815e2cf4>] lock_trace+0x44/0xc0 fs/proc/base.c:448
 [<ffffffff815e2fac>] proc_pid_personality+0x1c/0xc0 fs/proc/base.c:2835
 [<ffffffff815db19d>] proc_single_show+0xfd/0x170 fs/proc/base.c:791
 [<ffffffff815017f6>] seq_read+0x4b6/0x12b0 fs/seq_file.c:240
 [<ffffffff81491518>] do_loop_readv_writev+0x148/0x1e0 fs/read_write.c:680
 [<ffffffff81493351>] do_readv_writev+0x581/0x6f0 fs/read_write.c:810
 [<ffffffff81493538>] vfs_readv+0x78/0xb0 fs/read_write.c:834
 [<ffffffff8152f6df>] kernel_readv fs/splice.c:586 [inline]
 [<ffffffff8152f6df>] default_file_splice_read+0x50f/0x8f0 fs/splice.c:662
 [<ffffffff8152b5b7>] do_splice_to+0xf7/0x140 fs/splice.c:1154
 [<ffffffff8152b842>] splice_direct_to_actor+0x242/0x830 fs/splice.c:1226
 [<ffffffff8152bfd3>] do_splice_direct+0x1a3/0x270 fs/splice.c:1337
 [<ffffffff81494774>] do_sendfile+0x4e4/0xb80 fs/read_write.c:1227
 [<ffffffff81496763>] SYSC_sendfile64 fs/read_write.c:1282 [inline]
 [<ffffffff81496763>] SyS_sendfile64+0xc3/0x150 fs/read_write.c:1274
 [<ffffffff82705ca1>] entry_SYSCALL_64_fastpath+0x1e/0x9a