======================================================
WARNING: possible circular locking dependency detected
5.1.0-rc1+ #32 Not tainted
------------------------------------------------------
syz-executor.4/15230 is trying to acquire lock:
00000000e23bfa7b (&pipe->mutex/1){+.+.}, at: __pipe_lock fs/pipe.c:83 [inline]
00000000e23bfa7b (&pipe->mutex/1){+.+.}, at: fifo_open+0x159/0xb00 fs/pipe.c:930

but task is already holding lock:
00000000e75983c9 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1407 [inline]
00000000e75983c9 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x376/0x23f0 fs/exec.c:1750

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&sig->cred_guard_mutex){+.+.}:
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072
       mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:1102
       lock_trace+0x4a/0xe0 fs/proc/base.c:388
       proc_pid_syscall+0x98/0x250 fs/proc/base.c:623
       proc_single_show+0xf6/0x170 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+0xf0/0x160 fs/read_write.c:983
       kernel_readv fs/splice.c:358 [inline]
       default_file_splice_read+0x475/0x890 fs/splice.c:413
       do_splice_to+0x12a/0x190 fs/splice.c:876
       splice_direct_to_actor+0x2d2/0x970 fs/splice.c:953
       do_splice_direct+0x1da/0x2a0 fs/splice.c:1062
       do_sendfile+0x597/0xd00 fs/read_write.c:1442
       __do_compat_sys_sendfile fs/read_write.c:1524 [inline]
       __se_compat_sys_sendfile fs/read_write.c:1507 [inline]
       __ia32_compat_sys_sendfile+0x1f1/0x230 fs/read_write.c:1507
       do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
       do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
       entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

-> #1 (&p->lock){+.+.}:
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0xf7/0x1310 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+0x1fe/0x2c0 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+0xf0/0x160 fs/read_write.c:983
       kernel_readv fs/splice.c:358 [inline]
       default_file_splice_read+0x475/0x890 fs/splice.c:413
       do_splice_to+0x12a/0x190 fs/splice.c:876
       do_splice+0x10a9/0x13c0 fs/splice.c:1183
       __do_sys_splice fs/splice.c:1424 [inline]
       __se_sys_splice fs/splice.c:1404 [inline]
       __ia32_sys_splice+0x2c4/0x330 fs/splice.c:1404
       do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
       do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
       entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

-> #0 (&pipe->mutex/1){+.+.}:
       check_prevs_add kernel/locking/lockdep.c:2333 [inline]
       validate_chain kernel/locking/lockdep.c:2714 [inline]
       __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3701
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0xf7/0x1310 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:930
       do_dentry_open+0x488/0x1160 fs/open.c:771
       vfs_open+0xa0/0xd0 fs/open.c:880
       do_last fs/namei.c:3416 [inline]
       path_openat+0x10e9/0x46e0 fs/namei.c:3533
       do_filp_open+0x1a1/0x280 fs/namei.c:3563
       do_open_execat+0x137/0x690 fs/exec.c:856
       __do_execve_file.isra.0+0x178d/0x23f0 fs/exec.c:1758
       do_execveat_common fs/exec.c:1865 [inline]
       compat_do_execve fs/exec.c:1909 [inline]
       __do_compat_sys_execve fs/exec.c:1979 [inline]
       __se_compat_sys_execve fs/exec.c:1975 [inline]
       __ia32_compat_sys_execve+0x94/0xc0 fs/exec.c:1975
       do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
       do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
       entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz-executor.4/15230:
 #0: 00000000e75983c9 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1407 [inline]
 #0: 00000000e75983c9 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x376/0x23f0 fs/exec.c:1750

stack backtrace:
CPU: 0 PID: 15230 Comm: syz-executor.4 Not tainted 5.1.0-rc1+ #32
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+0x172/0x1f0 lib/dump_stack.c:113
 print_circular_bug.isra.0.cold+0x1cc/0x28f kernel/locking/lockdep.c:1571
 check_prev_add.constprop.0+0xf11/0x23c0 kernel/locking/lockdep.c:2220
 check_prevs_add kernel/locking/lockdep.c:2333 [inline]
 validate_chain kernel/locking/lockdep.c:2714 [inline]
 __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3701
 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
 __mutex_lock_common kernel/locking/mutex.c:925 [inline]
 __mutex_lock+0xf7/0x1310 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:930
 do_dentry_open+0x488/0x1160 fs/open.c:771
 vfs_open+0xa0/0xd0 fs/open.c:880
 do_last fs/namei.c:3416 [inline]
 path_openat+0x10e9/0x46e0 fs/namei.c:3533
 do_filp_open+0x1a1/0x280 fs/namei.c:3563
 do_open_execat+0x137/0x690 fs/exec.c:856
 __do_execve_file.isra.0+0x178d/0x23f0 fs/exec.c:1758
 do_execveat_common fs/exec.c:1865 [inline]
 compat_do_execve fs/exec.c:1909 [inline]
 __do_compat_sys_execve fs/exec.c:1979 [inline]
 __se_compat_sys_execve fs/exec.c:1975 [inline]
 __ia32_compat_sys_execve+0x94/0xc0 fs/exec.c:1975
 do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
 do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f86869
Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f5d820cc EFLAGS: 00000296 ORIG_RAX: 000000000000000b
RAX: ffffffffffffffda RBX: 0000000020000140 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000