====================================================== WARNING: possible circular locking dependency detected 5.0.0-next-20190306 #4 Not tainted ------------------------------------------------------ syz-executor904/7624 is trying to acquire lock: 000000004f9e4d56 (&pipe->mutex/1){+.+.}, at: __pipe_lock fs/pipe.c:83 [inline] 000000004f9e4d56 (&pipe->mutex/1){+.+.}, at: fifo_open+0x159/0xb00 fs/pipe.c:930 but task is already holding lock: 00000000a4a07b1b (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1407 [inline] 00000000a4a07b1b (&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: -> #1 (&sig->cred_guard_mutex){+.+.}: lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4202 __mutex_lock_common kernel/locking/mutex.c:925 [inline] __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072 mutex_lock_interruptible_nested+0x16/0x20 kernel/locking/mutex.c:1109 proc_pid_attr_write+0x200/0x580 fs/proc/base.c:2558 __vfs_write+0x8d/0x110 fs/read_write.c:485 __kernel_write+0x110/0x3b0 fs/read_write.c:506 write_pipe_buf+0x15d/0x1f0 fs/splice.c:793 splice_from_pipe_feed fs/splice.c:499 [inline] __splice_from_pipe+0x395/0x7d0 fs/splice.c:623 splice_from_pipe+0x108/0x170 fs/splice.c:658 default_file_splice_write+0x3c/0x90 fs/splice.c:805 do_splice_from fs/splice.c:847 [inline] do_splice+0x70a/0x13c0 fs/splice.c:1154 __do_sys_splice fs/splice.c:1424 [inline] __se_sys_splice fs/splice.c:1404 [inline] __x64_sys_splice+0x2c6/0x330 fs/splice.c:1404 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #0 (&pipe->mutex/1){+.+.}: check_prevs_add kernel/locking/lockdep.c:2324 [inline] validate_chain kernel/locking/lockdep.c:2705 [inline] __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3692 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4202 __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] do_execve fs/exec.c:1882 [inline] __do_sys_execve fs/exec.c:1958 [inline] __se_sys_execve fs/exec.c:1953 [inline] __x64_sys_execve+0x8f/0xc0 fs/exec.c:1953 do_syscall_64+0x103/0x610 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-executor904/7624: #0: 00000000a4a07b1b (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1407 [inline] #0: 00000000a4a07b1b (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x376/0x23f0 fs/exec.c:1750 stack backtrace: CPU: 0 PID: 7624 Comm: syz-executor904 Not tainted 5.0.0-next-20190306 #4 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:1562 check_prev_add.constprop.0+0xf11/0x23c0 kernel/locking/lockdep.c:2211 check_prevs_add kernel/locking/lockdep.c:2324 [inline] validate_chain kernel/locking/lockdep.c:2705 [inline] __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3692 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4202 __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] do_execve fs/exec.c:1882 [inline] __do_sys_execve fs/exec.c:1958 [inline] __se_sys_execve fs/exec.c:1953 [inline] __x64_sys_execve+0x8f/0xc0 fs/exec.c:1953 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x440289 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:00007ffe42f96318 EFLAGS: 00000246 ORIG_RAX: 000000000000003b RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440289 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000180 RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401b10 R13: 0000000000401ba0 R14: 0000000000000000 R15: 0000000000000000