syzbot

======================================================
WARNING: possible circular locking dependency detected
5.0.0-rc7+ #79 Not tainted
------------------------------------------------------
syz-executor078/7863 is trying to acquire lock:
00000000ce924167 (&sig->cred_guard_mutex){+.+.}, at: proc_pid_attr_write+0x1fa/0x530 fs/proc/base.c:2573

but task is already holding lock:
000000001577bd72 (&pipe->mutex/1){+.+.}, at: pipe_lock_nested fs/pipe.c:62 [inline]
000000001577bd72 (&pipe->mutex/1){+.+.}, at: pipe_lock+0x6e/0x80 fs/pipe.c:70

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&pipe->mutex/1){+.+.}:
       __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:905
       do_dentry_open+0x47d/0x1130 fs/open.c:771
       vfs_open+0xa0/0xd0 fs/open.c:880
       do_last fs/namei.c:3418 [inline]
       path_openat+0x10d7/0x4690 fs/namei.c:3534
       do_filp_open+0x1a1/0x280 fs/namei.c:3564
       do_open_execat+0x13b/0x6d0 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:1963 [inline]
       __se_sys_execve fs/exec.c:1958 [inline]
       __x64_sys_execve+0x8f/0xc0 fs/exec.c:1958
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&sig->cred_guard_mutex){+.+.}:
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:3841
       __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+0x1fa/0x530 fs/proc/base.c:2573
       __vfs_write+0x116/0x8e0 fs/read_write.c:485
       __kernel_write+0x110/0x3b0 fs/read_write.c:506
       write_pipe_buf+0x15d/0x1f0 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+0x108/0x170 fs/splice.c:662
       default_file_splice_write+0x3c/0x90 fs/splice.c:809
       do_splice_from fs/splice.c:851 [inline]
       do_splice+0x644/0x1330 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+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(&pipe->mutex/1);
                               lock(&sig->cred_guard_mutex);
                               lock(&pipe->mutex/1);
  lock(&sig->cred_guard_mutex);

 *** DEADLOCK ***

2 locks held by syz-executor078/7863:
 #0: 00000000f2e0ce39 (sb_writers#6){.+.+}, at: file_start_write include/linux/fs.h:2816 [inline]
 #0: 00000000f2e0ce39 (sb_writers#6){.+.+}, at: do_splice+0xceb/0x1330 fs/splice.c:1151
 #1: 000000001577bd72 (&pipe->mutex/1){+.+.}, at: pipe_lock_nested fs/pipe.c:62 [inline]
 #1: 000000001577bd72 (&pipe->mutex/1){+.+.}, at: pipe_lock+0x6e/0x80 fs/pipe.c:70

stack backtrace:
CPU: 1 PID: 7863 Comm: syz-executor078 Not tainted 5.0.0-rc7+ #79
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: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+0x2f00/0x4700 kernel/locking/lockdep.c:3338
 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:3841
 __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+0x1fa/0x530 fs/proc/base.c:2573
 __vfs_write+0x116/0x8e0 fs/read_write.c:485
 __kernel_write+0x110/0x3b0 fs/read_write.c:506
 write_pipe_buf+0x15d/0x1f0 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+0x108/0x170 fs/splice.c:662
 default_file_splice_write+0x3c/0x90 fs/splice.c:809
 do_splice_from fs/splice.c:851 [inline]
 do_splice+0x644/0x1330 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+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x445779
Code: e8 6c b6 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fc8cda61da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00000000006dac68 RCX: 0000000000445779
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00000000006dac60 R08: 0000020000000003 R09: 0000000000000009
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac6c
R13: 00007ffed72eae3f R14: 00007fc8cda629c0 R15: 20c49ba5e353f7cf