====================================================== WARNING: possible circular locking dependency detected 4.20.0-next-20190102 #2 Not tainted ------------------------------------------------------ syz-executor146/8075 is trying to acquire lock: 00000000a15e08ef (&pipe->mutex/1){+.+.}, at: __pipe_lock fs/pipe.c:83 [inline] 00000000a15e08ef (&pipe->mutex/1){+.+.}, at: fifo_open+0x159/0xb00 fs/pipe.c:905 but task is already holding lock: 000000009da69b22 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1407 [inline] 000000009da69b22 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x26d0 fs/exec.c:1750 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&sig->cred_guard_mutex){+.+.}: __mutex_lock_common kernel/locking/mutex.c:925 [inline] __mutex_lock+0x12f/0x1670 kernel/locking/mutex.c:1072 mutex_lock_interruptible_nested+0x16/0x20 kernel/locking/mutex.c:1109 proc_pid_attr_write+0x1fa/0x530 fs/proc/base.c:2560 __vfs_write+0x116/0xb40 fs/read_write.c:485 __kernel_write+0x110/0x3b0 fs/read_write.c:506 write_pipe_buf+0x180/0x240 fs/splice.c:797 splice_from_pipe_feed fs/splice.c:503 [inline] __splice_from_pipe+0x39a/0x7e0 fs/splice.c:627 splice_from_pipe+0x1ea/0x310 fs/splice.c:662 default_file_splice_write+0x3c/0x90 fs/splice.c:809 do_splice_from fs/splice.c:851 [inline] do_splice+0x64b/0x1410 fs/splice.c:1152 __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 -> #0 (&pipe->mutex/1){+.+.}: lock_acquire+0x1db/0x570 kernel/locking/lockdep.c:3841 __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:905 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+0x1939/0x26d0 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 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&sig->cred_guard_mutex); lock(&pipe->mutex/1); lock(&sig->cred_guard_mutex); lock(&pipe->mutex/1); *** DEADLOCK *** 1 lock held by syz-executor146/8075: #0: 000000009da69b22 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1407 [inline] #0: 000000009da69b22 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x26d0 fs/exec.c:1750 stack backtrace: CPU: 1 PID: 8075 Comm: syz-executor146 Not tainted 4.20.0-next-20190102 #2 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:1224 check_prev_add kernel/locking/lockdep.c:1866 [inline] check_prevs_add kernel/locking/lockdep.c:1979 [inline] validate_chain kernel/locking/lockdep.c:2350 [inline] __lock_acquire+0x2fed/0x4a10 kernel/locking/lockdep.c:3338 lock_acquire+0x1db/0x570 kernel/locking/lockdep.c:3841 __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:905 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+0x1939/0x26d0 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 RIP: 0033:0x440119 Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007ffde5d98a58 EFLAGS: 00000217 ORIG_RAX: 000000000000003b RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 0000000000440119 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000340 RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000217 R12: 00000000004019a0 R13: 0000000000401a30 R14: 0000000000000000 R15: 0000000000000000