[syzbot] possible deadlock in __btrfs_tree_lock

From: syzbot
Date: Fri Nov 18 2022 - 15:49:55 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 84368d882b96 Merge tag 'soc-fixes-6.1-3' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14bf6c21880000
kernel config: https://syzkaller.appspot.com/x/.config?x=6f4e5e9899396248
dashboard link: https://syzkaller.appspot.com/bug?extid=39feedae0c1e29951744
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c5385d467ad9/disk-84368d88.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9d5d70ca8a42/vmlinux-84368d88.xz
kernel image: https://storage.googleapis.com/syzbot-assets/da0dc29fc9f3/bzImage-84368d88.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+39feedae0c1e29951744@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
6.1.0-rc5-syzkaller-00144-g84368d882b96 #0 Not tainted
------------------------------------------------------
syz-executor.2/3014 is trying to acquire lock:
ffff888027f2a598 (&mm->mmap_lock#2){++++}-{3:3}, at: __might_fault+0xa9/0x180 mm/memory.c:5645

but task is already holding lock:
ffff888074c05838 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x350 fs/btrfs/locking.c:134

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #5 (btrfs-root-00){++++}-{3:3}:
down_write_nested+0x98/0x220 kernel/locking/rwsem.c:1672
__btrfs_tree_lock+0x32/0x3d0 fs/btrfs/locking.c:196
btrfs_tree_lock fs/btrfs/locking.c:203 [inline]
btrfs_lock_root_node+0x61/0x90 fs/btrfs/locking.c:256
commit_cowonly_roots+0x13c/0xa10 fs/btrfs/transaction.c:1266
btrfs_commit_transaction+0xb93/0x36e0 fs/btrfs/transaction.c:2376
btrfs_commit_super+0xc5/0x100 fs/btrfs/disk-io.c:4499
close_ctree+0x39c/0xdc7 fs/btrfs/disk-io.c:4653
generic_shutdown_super+0x158/0x410 fs/super.c:492
kill_anon_super+0x3a/0x60 fs/super.c:1086
btrfs_kill_super+0x3c/0x50 fs/btrfs/super.c:2441
deactivate_locked_super+0x98/0x160 fs/super.c:332
deactivate_super+0xb1/0xd0 fs/super.c:363
cleanup_mnt+0x2ae/0x3d0 fs/namespace.c:1186
task_work_run+0x16f/0x270 kernel/task_work.c:179
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
exit_to_user_mode_prepare+0x23c/0x250 kernel/entry/common.c:203
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #4 (&fs_info->reloc_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x12f/0x1360 kernel/locking/mutex.c:747
btrfs_record_root_in_trans+0x13d/0x1b0 fs/btrfs/transaction.c:484
start_transaction+0x295/0x1470 fs/btrfs/transaction.c:721
btrfs_create_common+0x1aa/0x260 fs/btrfs/inode.c:6633
btrfs_create+0x116/0x160 fs/btrfs/inode.c:6679
lookup_open.isra.0+0xf05/0x12a0 fs/namei.c:3413
open_last_lookups fs/namei.c:3481 [inline]
path_openat+0x996/0x2860 fs/namei.c:3710
do_filp_open+0x1ba/0x410 fs/namei.c:3740
do_sys_openat2+0x16d/0x4c0 fs/open.c:1310
do_sys_open fs/open.c:1326 [inline]
__do_sys_open fs/open.c:1334 [inline]
__se_sys_open fs/open.c:1330 [inline]
__x64_sys_open+0x11d/0x1c0 fs/open.c:1330
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
join_transaction+0x1b3/0x10f0 fs/btrfs/transaction.c:299
start_transaction+0x407/0x1470 fs/btrfs/transaction.c:658
btrfs_commit_super+0x9d/0x100 fs/btrfs/disk-io.c:4496
close_ctree+0x39c/0xdc7 fs/btrfs/disk-io.c:4653
generic_shutdown_super+0x158/0x410 fs/super.c:492
kill_anon_super+0x3a/0x60 fs/super.c:1086
btrfs_kill_super+0x3c/0x50 fs/btrfs/super.c:2441
deactivate_locked_super+0x98/0x160 fs/super.c:332
deactivate_super+0xb1/0xd0 fs/super.c:363
cleanup_mnt+0x2ae/0x3d0 fs/namespace.c:1186
task_work_run+0x16f/0x270 kernel/task_work.c:179
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
exit_to_user_mode_prepare+0x23c/0x250 kernel/entry/common.c:203
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
__lock_release kernel/locking/lockdep.c:5382 [inline]
lock_release+0x371/0x810 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 include/linux/fs.h:1877 [inline]
__btrfs_end_transaction+0x5c6/0x930 fs/btrfs/transaction.c:995
btrfs_dirty_inode+0x174/0x250 fs/btrfs/inode.c:6099
btrfs_update_time+0x25a/0x2c0 fs/btrfs/inode.c:6127
inode_update_time fs/inode.c:1871 [inline]
__file_update_time fs/inode.c:2088 [inline]
file_update_time+0x1fb/0x270 fs/inode.c:2119
btrfs_page_mkwrite+0x4f1/0x1140 fs/btrfs/inode.c:8431
do_page_mkwrite+0x19b/0x680 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+0x2280/0x3a40 mm/memory.c:5097
handle_mm_fault+0x1cc/0x780 mm/memory.c:5218
do_user_addr_fault+0x475/0x1210 arch/x86/mm/fault.c:1428
handle_page_fault arch/x86/mm/fault.c:1519 [inline]
exc_page_fault+0x98/0x170 arch/x86/mm/fault.c:1575
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570

-> #1 (sb_pagefaults#2){.+.+}-{0:0}:
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+0x1b5/0x1140 fs/btrfs/inode.c:8415
do_page_mkwrite+0x19b/0x680 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+0x2280/0x3a40 mm/memory.c:5097
handle_mm_fault+0x1cc/0x780 mm/memory.c:5218
do_user_addr_fault+0x475/0x1210 arch/x86/mm/fault.c:1428
handle_page_fault arch/x86/mm/fault.c:1519 [inline]
exc_page_fault+0x98/0x170 arch/x86/mm/fault.c:1575
asm_exc_page_fault+0x26/0x30 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 kernel/locking/lockdep.c:3831 [inline]
__lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5055
lock_acquire kernel/locking/lockdep.c:5668 [inline]
lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633
__might_fault mm/memory.c:5646 [inline]
__might_fault+0x10c/0x180 mm/memory.c:5639
_copy_to_user+0x29/0x150 lib/usercopy.c:29
copy_to_user include/linux/uaccess.h:169 [inline]
btrfs_ioctl_get_subvol_rootref+0x74e/0xad0 fs/btrfs/ioctl.c:3203
btrfs_ioctl+0x2de6/0x5be0 fs/btrfs/ioctl.c:5556
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x197/0x210 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 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 --> &fs_info->reloc_mutex --> btrfs-root-00

Possible unsafe locking scenario:

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

*** DEADLOCK ***

1 lock held by syz-executor.2/3014:
#0: ffff888074c05838 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x350 fs/btrfs/locking.c:134

stack backtrace:
CPU: 0 PID: 3014 Comm: syz-executor.2 Not tainted 6.1.0-rc5-syzkaller-00144-g84368d882b96 #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+0xd1/0x138 lib/dump_stack.c:106
check_noncircular+0x25f/0x2e0 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 kernel/locking/lockdep.c:3831 [inline]
__lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5055
lock_acquire kernel/locking/lockdep.c:5668 [inline]
lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633
__might_fault mm/memory.c:5646 [inline]
__might_fault+0x10c/0x180 mm/memory.c:5639
_copy_to_user+0x29/0x150 lib/usercopy.c:29
copy_to_user include/linux/uaccess.h:169 [inline]
btrfs_ioctl_get_subvol_rootref+0x74e/0xad0 fs/btrfs/ioctl.c:3203
btrfs_ioctl+0x2de6/0x5be0 fs/btrfs/ioctl.c:5556
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x197/0x210 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7ff87c68b639
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff87d4d8168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ff87c7abf80 RCX: 00007ff87c68b639
RDX: 0000000020002100 RSI: 00000000d000943d RDI: 0000000000000004
RBP: 00007ff87c6e6ae9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffc712f14ff R14: 00007ff87d4d8300 R15: 0000000000022000
</TASK>

---
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