syzbot

======================================================
WARNING: possible circular locking dependency detected
5.4.0-rc4+ #0 Not tainted
------------------------------------------------------
syz-executor.0/17400 is trying to acquire lock:
ffff88805f4450d0 (&sig->cred_guard_mutex){+.+.}, at: do_io_accounting fs/proc/base.c:2773 [inline]
ffff88805f4450d0 (&sig->cred_guard_mutex){+.+.}, at: proc_tid_io_accounting+0x156/0x200 fs/proc/base.c:2816

but task is already holding lock:
ffff88805d75a0a0 (&p->lock){+.+.}, at: seq_read+0x6e/0xd70 fs/seq_file.c:161

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&p->lock){+.+.}:
       lock_acquire+0x158/0x250 kernel/locking/lockdep.c:4487
       __mutex_lock_common+0x14c/0x2e20 kernel/locking/mutex.c:956
       __mutex_lock kernel/locking/mutex.c:1103 [inline]
       mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1118
       seq_read+0x6e/0xd70 fs/seq_file.c:161
       proc_reg_read+0x1e2/0x2d0 fs/proc/inode.c:223
       do_loop_readv_writev fs/read_write.c:714 [inline]
       do_iter_read+0x4b1/0x5b0 fs/read_write.c:935
       vfs_readv+0xc2/0x120 fs/read_write.c:997
       kernel_readv fs/splice.c:359 [inline]
       default_file_splice_read+0x544/0x8d0 fs/splice.c:414
       do_splice_to fs/splice.c:877 [inline]
       splice_direct_to_actor+0x39c/0xac0 fs/splice.c:954
       do_splice_direct+0x200/0x330 fs/splice.c:1063
       do_sendfile+0x7e4/0xfd0 fs/read_write.c:1464
       __do_sys_sendfile64 fs/read_write.c:1525 [inline]
       __se_sys_sendfile64 fs/read_write.c:1511 [inline]
       __x64_sys_sendfile64+0x176/0x1b0 fs/read_write.c:1511
       do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (sb_writers#3){.+.+}:
       lock_acquire+0x158/0x250 kernel/locking/lockdep.c:4487
       percpu_down_read include/linux/percpu-rwsem.h:40 [inline]
       __sb_start_write+0xeb/0x430 fs/super.c:1672
       sb_start_write include/linux/fs.h:1650 [inline]
       mnt_want_write+0x4a/0xa0 fs/namespace.c:354
       ovl_want_write+0x77/0x80 fs/overlayfs/util.c:21
       ovl_setattr+0x55/0x790 fs/overlayfs/inode.c:27
       notify_change+0xa27/0xe70 fs/attr.c:337
       chown_common+0x3a4/0x5f0 fs/open.c:652
       do_fchownat+0x113/0x1c0 fs/open.c:682
       __do_sys_lchown fs/open.c:707 [inline]
       __se_sys_lchown fs/open.c:705 [inline]
       __x64_sys_lchown+0x85/0x90 fs/open.c:705
       do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&ovl_i_mutex_dir_key[depth]){++++}:
       lock_acquire+0x158/0x250 kernel/locking/lockdep.c:4487
       down_read+0x39/0x50 kernel/locking/rwsem.c:1495
       inode_lock_shared include/linux/fs.h:801 [inline]
       do_last fs/namei.c:3313 [inline]
       path_openat+0xa9a/0x4420 fs/namei.c:3525
       do_filp_open+0x192/0x3d0 fs/namei.c:3555
       do_open_execat+0xff/0x610 fs/exec.c:857
       __do_execve_file+0x766/0x1cc0 fs/exec.c:1762
       do_execveat_common fs/exec.c:1868 [inline]
       do_execve fs/exec.c:1885 [inline]
       __do_sys_execve fs/exec.c:1961 [inline]
       __se_sys_execve fs/exec.c:1956 [inline]
       __x64_sys_execve+0x94/0xb0 fs/exec.c:1956
       do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&sig->cred_guard_mutex){+.+.}:
       check_prev_add kernel/locking/lockdep.c:2476 [inline]
       check_prevs_add kernel/locking/lockdep.c:2581 [inline]
       validate_chain+0x161e/0x7bc0 kernel/locking/lockdep.c:2971
       __lock_acquire+0xc75/0x1be0 kernel/locking/lockdep.c:3955
       lock_acquire+0x158/0x250 kernel/locking/lockdep.c:4487
       __mutex_lock_common+0x14c/0x2e20 kernel/locking/mutex.c:956
       __mutex_lock kernel/locking/mutex.c:1103 [inline]
       mutex_lock_killable_nested+0x1b/0x30 kernel/locking/mutex.c:1133
       do_io_accounting fs/proc/base.c:2773 [inline]
       proc_tid_io_accounting+0x156/0x200 fs/proc/base.c:2816
       proc_single_show+0xd8/0x120 fs/proc/base.c:756
       seq_read+0x4cd/0xd70 fs/seq_file.c:229
       do_loop_readv_writev fs/read_write.c:714 [inline]
       do_iter_read+0x4b1/0x5b0 fs/read_write.c:935
       vfs_readv fs/read_write.c:997 [inline]
       do_preadv+0x178/0x290 fs/read_write.c:1089
       __do_sys_preadv fs/read_write.c:1139 [inline]
       __se_sys_preadv fs/read_write.c:1134 [inline]
       __x64_sys_preadv+0x9e/0xb0 fs/read_write.c:1134
       do_syscall_64+0xf7/0x1c0 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 --> sb_writers#3 --> &p->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&p->lock);
                               lock(sb_writers#3);
                               lock(&p->lock);
  lock(&sig->cred_guard_mutex);

 *** DEADLOCK ***

1 lock held by syz-executor.0/17400:
 #0: ffff88805d75a0a0 (&p->lock){+.+.}, at: seq_read+0x6e/0xd70 fs/seq_file.c:161

stack backtrace:
CPU: 1 PID: 17400 Comm: syz-executor.0 Not tainted 5.4.0-rc4+ #0
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+0x1d8/0x2f8 lib/dump_stack.c:113
 print_circular_bug+0xc2d/0xe60 kernel/locking/lockdep.c:1685
 check_noncircular+0x206/0x3a0 kernel/locking/lockdep.c:1809
 check_prev_add kernel/locking/lockdep.c:2476 [inline]
 check_prevs_add kernel/locking/lockdep.c:2581 [inline]
 validate_chain+0x161e/0x7bc0 kernel/locking/lockdep.c:2971
 __lock_acquire+0xc75/0x1be0 kernel/locking/lockdep.c:3955
 lock_acquire+0x158/0x250 kernel/locking/lockdep.c:4487
 __mutex_lock_common+0x14c/0x2e20 kernel/locking/mutex.c:956
 __mutex_lock kernel/locking/mutex.c:1103 [inline]
 mutex_lock_killable_nested+0x1b/0x30 kernel/locking/mutex.c:1133
 do_io_accounting fs/proc/base.c:2773 [inline]
 proc_tid_io_accounting+0x156/0x200 fs/proc/base.c:2816
 proc_single_show+0xd8/0x120 fs/proc/base.c:756
 seq_read+0x4cd/0xd70 fs/seq_file.c:229
 do_loop_readv_writev fs/read_write.c:714 [inline]
 do_iter_read+0x4b1/0x5b0 fs/read_write.c:935
 vfs_readv fs/read_write.c:997 [inline]
 do_preadv+0x178/0x290 fs/read_write.c:1089
 __do_sys_preadv fs/read_write.c:1139 [inline]
 __se_sys_preadv fs/read_write.c:1134 [inline]
 __x64_sys_preadv+0x9e/0xb0 fs/read_write.c:1134
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459ef9
Code: ad b6 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffa4f49ec78 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000459ef9
RDX: 0000000000000001 RSI: 0000000020000980 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffa4f49f6d4
R13: 00000000004c75cc R14: 00000000004dcf78 R15: 00000000ffffffff