======================================================
WARNING: possible circular locking dependency detected
5.0.0-rc3-next-20190123 #18 Not tainted
------------------------------------------------------
syz-executor2/18026 is trying to acquire lock:
000000008185cdbc (&sig->cred_guard_mutex){+.+.}, at: do_io_accounting+0x1d1/0xfe0 fs/proc/base.c:2744

but task is already holding lock:
000000000ea226f4 (&p->lock){+.+.}, at: seq_read+0x71/0x1130 fs/seq_file.c:161

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&p->lock){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0x12f/0x1670 kernel/locking/mutex.c:1072
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
       seq_read+0x71/0x1130 fs/seq_file.c:161
       proc_reg_read+0x29a/0x3c0 fs/proc/inode.c:227
       do_loop_readv_writev fs/read_write.c:700 [inline]
       do_loop_readv_writev fs/read_write.c:687 [inline]
       do_iter_read+0x4a9/0x660 fs/read_write.c:921
       vfs_readv+0x175/0x1c0 fs/read_write.c:983
       kernel_readv fs/splice.c:362 [inline]
       default_file_splice_read+0x50c/0xac0 fs/splice.c:417
       do_splice_to+0x12a/0x190 fs/splice.c:880
       do_splice+0xff7/0x1410 fs/splice.c:1178
       __do_sys_splice fs/splice.c:1419 [inline]
       __se_sys_splice fs/splice.c:1399 [inline]
       __x64_sys_splice+0x2c6/0x330 fs/splice.c:1399
       do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&pipe->mutex/1){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0x12f/0x1670 kernel/locking/mutex.c:1072
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
       __pipe_lock fs/pipe.c:83 [inline]
       fifo_open+0x159/0xb00 fs/pipe.c:904
       do_dentry_open+0x495/0x1230 fs/open.c:771
       vfs_open+0xa0/0xd0 fs/open.c:880
       do_last fs/namei.c:3418 [inline]
       path_openat+0x144f/0x5660 fs/namei.c:3534
       do_filp_open+0x26f/0x370 fs/namei.c:3564
       do_open_execat+0x207/0x8e0 fs/exec.c:856
       __do_execve_file.isra.0+0x1966/0x2700 fs/exec.c:1758
       do_execveat_common fs/exec.c:1865 [inline]
       do_execve fs/exec.c:1882 [inline]
       __do_sys_execve fs/exec.c:1963 [inline]
       __se_sys_execve fs/exec.c:1958 [inline]
       __x64_sys_execve+0x8f/0xc0 fs/exec.c:1958
       do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&sig->cred_guard_mutex){+.+.}:
       lock_acquire+0x1db/0x570 kernel/locking/lockdep.c:3845
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0x12f/0x1670 kernel/locking/mutex.c:1072
       mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:1102
       do_io_accounting+0x1d1/0xfe0 fs/proc/base.c:2744
       proc_tgid_io_accounting+0x23/0x30 fs/proc/base.c:2793
       proc_single_show+0xf6/0x180 fs/proc/base.c:743
       seq_read+0x4db/0x1130 fs/seq_file.c:229
       do_loop_readv_writev fs/read_write.c:700 [inline]
       do_loop_readv_writev fs/read_write.c:687 [inline]
       do_iter_read+0x4a9/0x660 fs/read_write.c:921
       vfs_readv+0x175/0x1c0 fs/read_write.c:983
       do_readv+0x11a/0x300 fs/read_write.c:1016
       __do_sys_readv fs/read_write.c:1103 [inline]
       __se_sys_readv fs/read_write.c:1100 [inline]
       __x64_sys_readv+0x75/0xb0 fs/read_write.c:1100
       do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
  &sig->cred_guard_mutex --> &pipe->mutex/1 --> &p->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&p->lock);
                               lock(&pipe->mutex/1);
                               lock(&p->lock);
  lock(&sig->cred_guard_mutex);

 *** DEADLOCK ***

2 locks held by syz-executor2/18026:
 #0: 00000000aaf741d5 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1b3/0x1f0 fs/file.c:796
 #1: 000000000ea226f4 (&p->lock){+.+.}, at: seq_read+0x71/0x1130 fs/seq_file.c:161

stack backtrace:
CPU: 0 PID: 18026 Comm: syz-executor2 Not tainted 5.0.0-rc3-next-20190123 #18
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1db/0x2d0 lib/dump_stack.c:113
 print_circular_bug.isra.0.cold+0x1cc/0x28f kernel/locking/lockdep.c:1225
 check_prev_add kernel/locking/lockdep.c:1856 [inline]
 check_prevs_add kernel/locking/lockdep.c:1969 [inline]
 validate_chain kernel/locking/lockdep.c:2340 [inline]
 __lock_acquire+0x2fed/0x4a10 kernel/locking/lockdep.c:3321
 lock_acquire+0x1db/0x570 kernel/locking/lockdep.c:3845
 __mutex_lock_common kernel/locking/mutex.c:925 [inline]
 __mutex_lock+0x12f/0x1670 kernel/locking/mutex.c:1072
 mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:1102
 do_io_accounting+0x1d1/0xfe0 fs/proc/base.c:2744
 proc_tgid_io_accounting+0x23/0x30 fs/proc/base.c:2793
 proc_single_show+0xf6/0x180 fs/proc/base.c:743
 seq_read+0x4db/0x1130 fs/seq_file.c:229
 do_loop_readv_writev fs/read_write.c:700 [inline]
 do_loop_readv_writev fs/read_write.c:687 [inline]
 do_iter_read+0x4a9/0x660 fs/read_write.c:921
 vfs_readv+0x175/0x1c0 fs/read_write.c:983
 do_readv+0x11a/0x300 fs/read_write.c:1016
 __do_sys_readv fs/read_write.c:1103 [inline]
 __se_sys_readv fs/read_write.c:1100 [inline]
 __x64_sys_readv+0x75/0xb0 fs/read_write.c:1100
 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x458099
Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8bfd75bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000013
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458099
RDX: 0000000000000001 RSI: 0000000020000440 RDI: 0000000000000003
RBP: 000000000073bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f8bfd75c6d4
R13: 00000000004c4b0b R14: 00000000004d8458 R15: 00000000ffffffff