syzbot

======================================================
WARNING: possible circular locking dependency detected
6.1.0-rc6-syzkaller-00176-g08ad43d554ba #0 Not tainted
------------------------------------------------------
syz-executor.5/6024 is trying to acquire lock:
ffff88807772acd8 (&mm->mmap_lock#2){++++}-{3:3}, at: __might_fault+0x8f/0x110 mm/memory.c:5645

but task is already holding lock:
ffff888028c7aaa8 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
ffff888028c7aaa8 (btrfs-root-00){++++}-{3:3}, at: btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
ffff888028c7aaa8 (btrfs-root-00){++++}-{3:3}, at: btrfs_read_lock_root_node+0x2b4/0x400 fs/btrfs/locking.c:279

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (btrfs-root-00){++++}-{3:3}:
       lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5668
       down_read_nested+0x3c/0x50 kernel/locking/rwsem.c:1634
       __btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
       btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
       btrfs_read_lock_root_node+0x2b4/0x400 fs/btrfs/locking.c:279
       btrfs_search_forward+0x10f/0xe70 fs/btrfs/ctree.c:4488
       btrfs_uuid_scan_kthread+0x25e/0xbc0 fs/btrfs/volumes.c:4654
       kthread+0x266/0x300 kernel/kthread.c:376
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
       lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5668
       join_transaction+0x19f/0xe60 fs/btrfs/transaction.c:299
       start_transaction+0x6fb/0x1180 fs/btrfs/transaction.c:658
       btrfs_create_common+0x2c6/0x420 fs/btrfs/inode.c:6633
       lookup_open fs/namei.c:3413 [inline]
       open_last_lookups fs/namei.c:3481 [inline]
       path_openat+0x12d0/0x2df0 fs/namei.c:3710
       do_filp_open+0x264/0x4f0 fs/namei.c:3740
       do_sys_openat2+0x124/0x4e0 fs/open.c:1310
       do_sys_open fs/open.c:1326 [inline]
       __do_sys_openat fs/open.c:1342 [inline]
       __se_sys_openat fs/open.c:1337 [inline]
       __x64_sys_openat+0x243/0x290 fs/open.c:1337
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
       reacquire_held_locks+0x386/0x650 kernel/locking/lockdep.c:5193
       __lock_release kernel/locking/lockdep.c:5382 [inline]
       lock_release+0x2e2/0x820 kernel/locking/lockdep.c:5688
       percpu_up_read include/linux/percpu-rwsem.h:99 [inline]
       __sb_end_write include/linux/fs.h:1821 [inline]
       sb_end_intwrite+0x1e/0x1a0 include/linux/fs.h:1877
       __btrfs_end_transaction+0x388/0x790 fs/btrfs/transaction.c:995
       btrfs_dirty_inode+0x177/0x1c0 fs/btrfs/inode.c:6099
       inode_update_time fs/inode.c:1871 [inline]
       __file_update_time fs/inode.c:2088 [inline]
       file_update_time+0x3df/0x5d0 fs/inode.c:2119
       btrfs_page_mkwrite+0x3a8/0xc80 fs/btrfs/inode.c:8431
       do_page_mkwrite+0x19e/0x5e0 mm/memory.c:2978
       do_shared_fault mm/memory.c:4619 [inline]
       do_fault mm/memory.c:4687 [inline]
       handle_pte_fault mm/memory.c:4955 [inline]
       __handle_mm_fault mm/memory.c:5097 [inline]
       handle_mm_fault+0x1c63/0x3630 mm/memory.c:5218
       do_user_addr_fault+0x69b/0xcb0 arch/x86/mm/fault.c:1428
       handle_page_fault arch/x86/mm/fault.c:1519 [inline]
       exc_page_fault+0x7a/0x110 arch/x86/mm/fault.c:1575
       asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:570

-> #1 (sb_pagefaults){.+.+}-{0:0}:
       lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5668
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1826 [inline]
       sb_start_pagefault include/linux/fs.h:1930 [inline]
       btrfs_page_mkwrite+0x1ea/0xc80 fs/btrfs/inode.c:8415
       do_page_mkwrite+0x19e/0x5e0 mm/memory.c:2978
       do_shared_fault mm/memory.c:4619 [inline]
       do_fault mm/memory.c:4687 [inline]
       handle_pte_fault mm/memory.c:4955 [inline]
       __handle_mm_fault mm/memory.c:5097 [inline]
       handle_mm_fault+0x1c63/0x3630 mm/memory.c:5218
       do_user_addr_fault+0x69b/0xcb0 arch/x86/mm/fault.c:1428
       handle_page_fault arch/x86/mm/fault.c:1519 [inline]
       exc_page_fault+0x7a/0x110 arch/x86/mm/fault.c:1575
       asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:570

-> #0 (&mm->mmap_lock#2){++++}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3097 [inline]
       check_prevs_add kernel/locking/lockdep.c:3216 [inline]
       validate_chain+0x1898/0x6ae0 kernel/locking/lockdep.c:3831
       __lock_acquire+0x1292/0x1f60 kernel/locking/lockdep.c:5055
       lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5668
       __might_fault+0xb2/0x110 mm/memory.c:5646
       _copy_to_user+0x26/0x130 lib/usercopy.c:29
       copy_to_user include/linux/uaccess.h:169 [inline]
       btrfs_ioctl_get_subvol_rootref+0x8cf/0xa90 fs/btrfs/ioctl.c:3203
       btrfs_ioctl+0xb7c/0xc10 fs/btrfs/ioctl.c:5556
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x63/0xcd

other info that might help us debug this:

Chain exists of:
  &mm->mmap_lock#2 --> btrfs_trans_num_extwriters --> btrfs-root-00

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(btrfs-root-00);
                               lock(btrfs_trans_num_extwriters);
                               lock(btrfs-root-00);
  lock(&mm->mmap_lock#2);

 *** DEADLOCK ***

1 lock held by syz-executor.5/6024:
 #0: ffff888028c7aaa8 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
 #0: ffff888028c7aaa8 (btrfs-root-00){++++}-{3:3}, at: btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
 #0: ffff888028c7aaa8 (btrfs-root-00){++++}-{3:3}, at: btrfs_read_lock_root_node+0x2b4/0x400 fs/btrfs/locking.c:279

stack backtrace:
CPU: 0 PID: 6024 Comm: syz-executor.5 Not tainted 6.1.0-rc6-syzkaller-00176-g08ad43d554ba #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
 check_noncircular+0x2cc/0x390 kernel/locking/lockdep.c:2177
 check_prev_add kernel/locking/lockdep.c:3097 [inline]
 check_prevs_add kernel/locking/lockdep.c:3216 [inline]
 validate_chain+0x1898/0x6ae0 kernel/locking/lockdep.c:3831
 __lock_acquire+0x1292/0x1f60 kernel/locking/lockdep.c:5055
 lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5668
 __might_fault+0xb2/0x110 mm/memory.c:5646
 _copy_to_user+0x26/0x130 lib/usercopy.c:29
 copy_to_user include/linux/uaccess.h:169 [inline]
 btrfs_ioctl_get_subvol_rootref+0x8cf/0xa90 fs/btrfs/ioctl.c:3203
 btrfs_ioctl+0xb7c/0xc10 fs/btrfs/ioctl.c:5556
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7feda468c0d9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007feda54d4168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007feda47abf80 RCX: 00007feda468c0d9
RDX: 0000000020000380 RSI: 00000000d000943d RDI: 0000000000000005
RBP: 00007feda46e7ae9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffda754475f R14: 00007feda54d4300 R15: 0000000000022000
 </TASK>