syzbot

overlayfs: workdir and upperdir must reside under the same mount
======================================================
WARNING: possible circular locking dependency detected
5.1.0-rc5+ #74 Not tainted
------------------------------------------------------
syz-executor520/11107 is trying to acquire lock:
00000000efa5fd95 (sb_writers#5){.+.+}, at: sb_start_write include/linux/fs.h:1621 [inline]
00000000efa5fd95 (sb_writers#5){.+.+}, at: mnt_want_write+0x3f/0xc0 fs/namespace.c:358

but task is already holding lock:
00000000cf4aa2b1 (&ovl_i_mutex_dir_key[depth]#2){++++}, at: inode_lock include/linux/fs.h:772 [inline]
00000000cf4aa2b1 (&ovl_i_mutex_dir_key[depth]#2){++++}, at: vfs_rmdir fs/namei.c:3868 [inline]
00000000cf4aa2b1 (&ovl_i_mutex_dir_key[depth]#2){++++}, at: vfs_rmdir+0xe1/0x470 fs/namei.c:3857

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&ovl_i_mutex_dir_key[depth]#2){++++}:
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       down_read+0x3b/0x90 kernel/locking/rwsem.c:24
       inode_lock_shared include/linux/fs.h:782 [inline]
       do_last fs/namei.c:3321 [inline]
       path_openat+0x1e98/0x46e0 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

-> #3 (&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
       do_io_accounting+0x1f4/0x830 fs/proc/base.c:2740
       proc_tgid_io_accounting+0x23/0x30 fs/proc/base.c:2789
       proc_single_show+0xf6/0x170 fs/proc/base.c:744
       seq_read+0x4db/0x1130 fs/seq_file.c:229
       do_loop_readv_writev fs/read_write.c:701 [inline]
       do_loop_readv_writev fs/read_write.c:688 [inline]
       do_iter_read+0x4a9/0x660 fs/read_write.c:922
       vfs_readv+0xf0/0x160 fs/read_write.c:984
       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:1443
       __do_sys_sendfile64 fs/read_write.c:1504 [inline]
       __se_sys_sendfile64 fs/read_write.c:1490 [inline]
       __x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1490
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (&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:701 [inline]
       do_loop_readv_writev fs/read_write.c:688 [inline]
       do_iter_read+0x4a9/0x660 fs/read_write.c:922
       vfs_readv+0xf0/0x160 fs/read_write.c:984
       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+0x110b/0x1420 fs/splice.c:1183
       __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

-> #1 (&pipe->mutex/1){+.+.}:
       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_nested fs/pipe.c:62 [inline]
       pipe_lock+0x6e/0x80 fs/pipe.c:70
       iter_file_splice_write+0x18b/0xbe0 fs/splice.c:696
       do_splice_from fs/splice.c:847 [inline]
       do_splice+0x70a/0x1420 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 (sb_writers#5){.+.+}:
       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
       percpu_down_read include/linux/percpu-rwsem.h:36 [inline]
       __sb_start_write+0x20b/0x360 fs/super.c:1613
       sb_start_write include/linux/fs.h:1621 [inline]
       mnt_want_write+0x3f/0xc0 fs/namespace.c:358
       ovl_want_write+0x76/0xa0 fs/overlayfs/util.c:24
       ovl_do_remove+0xe9/0xd70 fs/overlayfs/dir.c:840
       ovl_rmdir+0x1b/0x20 fs/overlayfs/dir.c:890
       vfs_rmdir fs/namei.c:3878 [inline]
       vfs_rmdir+0x19c/0x470 fs/namei.c:3857
       do_rmdir+0x39e/0x420 fs/namei.c:3939
       __do_sys_rmdir fs/namei.c:3957 [inline]
       __se_sys_rmdir fs/namei.c:3955 [inline]
       __x64_sys_rmdir+0x36/0x40 fs/namei.c:3955
       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:

Chain exists of:
  sb_writers#5 --> &sig->cred_guard_mutex --> &ovl_i_mutex_dir_key[depth]#2

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ovl_i_mutex_dir_key[depth]#2);
                               lock(&sig->cred_guard_mutex);
                               lock(&ovl_i_mutex_dir_key[depth]#2);
  lock(sb_writers#5);

 *** DEADLOCK ***

3 locks held by syz-executor520/11107:
 #0: 00000000e91bc594 (sb_writers#8){.+.+}, at: sb_start_write include/linux/fs.h:1621 [inline]
 #0: 00000000e91bc594 (sb_writers#8){.+.+}, at: mnt_want_write+0x3f/0xc0 fs/namespace.c:358
 #1: 00000000483c3c1a (&ovl_i_mutex_dir_key[depth]/1){+.+.}, at: inode_lock_nested include/linux/fs.h:807 [inline]
 #1: 00000000483c3c1a (&ovl_i_mutex_dir_key[depth]/1){+.+.}, at: do_rmdir+0x271/0x420 fs/namei.c:3927
 #2: 00000000cf4aa2b1 (&ovl_i_mutex_dir_key[depth]#2){++++}, at: inode_lock include/linux/fs.h:772 [inline]
 #2: 00000000cf4aa2b1 (&ovl_i_mutex_dir_key[depth]#2){++++}, at: vfs_rmdir fs/namei.c:3868 [inline]
 #2: 00000000cf4aa2b1 (&ovl_i_mutex_dir_key[depth]#2){++++}, at: vfs_rmdir+0xe1/0x470 fs/namei.c:3857

stack backtrace:
CPU: 0 PID: 11107 Comm: syz-executor520 Not tainted 5.1.0-rc5+ #74
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
 percpu_down_read include/linux/percpu-rwsem.h:36 [inline]
 __sb_start_write+0x20b/0x360 fs/super.c:1613
 sb_start_write include/linux/fs.h:1621 [inline]
 mnt_want_write+0x3f/0xc0 fs/namespace.c:358
 ovl_want_write+0x76/0xa0 fs/overlayfs/util.c:24
 ovl_do_remove+0xe9/0xd70 fs/overlayfs/dir.c:840
 ovl_rmdir+0x1b/0x20 fs/overlayfs/dir.c:890
 vfs_rmdir fs/namei.c:3878 [inline]
 vfs_rmdir+0x19c/0x470 fs/namei.c:3857
 do_rmdir+0x39e/0x420 fs/namei.c:3939
 __do_sys_rmdir fs/namei.c:3957 [inline]
 __se_sys_rmdir fs/namei.c:3955 [inline]
 __x64_sys_rmdir+0x36/0x40 fs/namei.c:3955
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x447049
Code: e8 ec b9 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 db 06 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fbbfb3f0db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 00000000006dcc68 RCX: 0000000000447049
RDX: 0000000000447049 RSI: 0000000000000000 RDI: 0000000020000000
RBP: 00000000006dcc60 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc6c
R13: 00007ffea630b6df R14: 00007fbbfb3f19c0 R15: 0000000000000000