[syzbot] possible deadlock in btrfs_dirty_inode

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 094226ad94f4 Linux 6.1-rc5
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=152efa11880000
kernel config: https://syzkaller.appspot.com/x/.config?x=b338c1b9de0823a3
dashboard link: https://syzkaller.appspot.com/bug?extid=37edf86c9b60581e523f
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, 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/3b689839e3f5/disk-094226ad.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a4f2a27061e6/vmlinux-094226ad.xz
kernel image: https://storage.googleapis.com/syzbot-assets/37b109ab179c/bzImage-094226ad.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+37edf8...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.1.0-rc5-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.2/15801 is trying to acquire lock:
ffff88807b322650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_dirty_inode+0xcc/0x1c0 fs/btrfs/inode.c:6085

but task is already holding lock:
ffff888027b98fd8 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
ffff888027b98fd8 (&mm->mmap_lock#2){++++}-{3:3}, at: vm_mmap_pgoff+0x14d/0x2b0 mm/util.c:518

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&mm->mmap_lock#2){++++}-{3:3}:
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

-> #3 (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_slot_get_root fs/btrfs/ctree.c:1665 [inline]
btrfs_search_slot+0x495/0x2fe0 fs/btrfs/ctree.c:1985
__lookup_free_space_inode fs/btrfs/free-space-cache.c:87 [inline]
lookup_free_space_inode+0x272/0x820 fs/btrfs/free-space-cache.c:134
btrfs_remove_free_space_inode+0xe3/0x470 fs/btrfs/free-space-cache.c:246
cleanup_free_space_cache_v1 fs/btrfs/free-space-cache.c:4092 [inline]
btrfs_set_free_space_cache_v1_active+0xf1/0x210 fs/btrfs/free-space-cache.c:4120
btrfs_start_pre_rw_mount+0x3fe/0x660 fs/btrfs/disk-io.c:3265
open_ctree+0x27e6/0x2d6d fs/btrfs/disk-io.c:3792
btrfs_fill_super+0x1c6/0x2d0 fs/btrfs/super.c:1461
btrfs_mount_root+0x885/0x9a0 fs/btrfs/super.c:1829
legacy_get_tree+0xea/0x180 fs/fs_context.c:610
vfs_get_tree+0x88/0x270 fs/super.c:1531
fc_mount fs/namespace.c:1043 [inline]
vfs_kern_mount+0xc9/0x160 fs/namespace.c:1073
btrfs_mount+0x3d3/0xbb0 fs/btrfs/super.c:1889
legacy_get_tree+0xea/0x180 fs/fs_context.c:610
vfs_get_tree+0x88/0x270 fs/super.c:1531
do_new_mount+0x289/0xad0 fs/namespace.c:3040
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount+0x2d3/0x3c0 fs/namespace.c:3568
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_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

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5668
join_transaction+0x17a/0xe60 fs/btrfs/transaction.c:298
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

-> #0 (sb_internal#2){.+.+}-{0:0}:
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
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1826 [inline]
sb_start_intwrite include/linux/fs.h:1948 [inline]
start_transaction+0x5cb/0x1180 fs/btrfs/transaction.c:652
btrfs_dirty_inode+0xcc/0x1c0 fs/btrfs/inode.c:6085
inode_update_time fs/inode.c:1871 [inline]
touch_atime+0x315/0x630 fs/inode.c:1944
file_accessed include/linux/fs.h:2521 [inline]
btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:2333
call_mmap include/linux/fs.h:2196 [inline]
mmap_region+0xff6/0x1e00 mm/mmap.c:2625
do_mmap+0x8d9/0xf60 mm/mmap.c:1412
vm_mmap_pgoff+0x19e/0x2b0 mm/util.c:520
ksys_mmap_pgoff+0x48c/0x6d0 mm/mmap.c:1458
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:
sb_internal#2 --> btrfs-root-00 --> &mm->mmap_lock#2

Possible unsafe locking scenario:

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

*** DEADLOCK ***

2 locks held by syz-executor.2/15801:
#0: ffff888027b98fd8 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
#0: ffff888027b98fd8 (&mm->mmap_lock#2){++++}-{3:3}, at: vm_mmap_pgoff+0x14d/0x2b0 mm/util.c:518
#1: ffff88807b322460 (sb_writers#17){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2521 [inline]
#1: ffff88807b322460 (sb_writers#17){.+.+}-{0:0}, at: btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:2333

stack backtrace:
CPU: 1 PID: 15801 Comm: syz-executor.2 Not tainted 6.1.0-rc5-syzkaller #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
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1826 [inline]
sb_start_intwrite include/linux/fs.h:1948 [inline]
start_transaction+0x5cb/0x1180 fs/btrfs/transaction.c:652
btrfs_dirty_inode+0xcc/0x1c0 fs/btrfs/inode.c:6085
inode_update_time fs/inode.c:1871 [inline]
touch_atime+0x315/0x630 fs/inode.c:1944
file_accessed include/linux/fs.h:2521 [inline]
btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:2333
call_mmap include/linux/fs.h:2196 [inline]
mmap_region+0xff6/0x1e00 mm/mmap.c:2625
do_mmap+0x8d9/0xf60 mm/mmap.c:1412
vm_mmap_pgoff+0x19e/0x2b0 mm/util.c:520
ksys_mmap_pgoff+0x48c/0x6d0 mm/mmap.c:1458
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: 0033:0x7f4d3fe8b639
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:00007f4d40c4e168 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f4d3ffac050 RCX: 00007f4d3fe8b639
RDX: 0000000000000002 RSI: 0000000000b36000 RDI: 0000000020000000
RBP: 00007f4d3fee6ae9 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000028011 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffedddb50ff R14: 00007f4d40c4e300 R15: 0000000000022000
</TASK>


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: e01d50cbd6ee Merge tag 'vfio-v6.1-rc6' of https://github.c..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=149ca515880000
kernel config: https://syzkaller.appspot.com/x/.config?x=47b0b2ecc119b39f

dashboard link: https://syzkaller.appspot.com/bug?extid=37edf86c9b60581e523f
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=140c35d1880000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10df68e6880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b48e4d485e7e/disk-e01d50cb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dc9ba558e055/vmlinux-e01d50cb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b766d9815123/bzImage-e01d50cb.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/690a6e936871/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+37edf8...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected

6.1.0-rc5-syzkaller-00008-ge01d50cbd6ee #0 Not tainted
------------------------------------------------------
syz-executor589/3733 is trying to acquire lock:
ffff88807658c650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_dirty_inode+0xcc/0x1c0 fs/btrfs/inode.c:6085

but task is already holding lock:

ffff88807d23acd8 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
ffff88807d23acd8 (&mm->mmap_lock#2){++++}-{3:3}, at: vm_mmap_pgoff+0x14d/0x2b0 mm/util.c:518

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&mm->mmap_lock#2){++++}-{3:3}:

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

-> #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_slot_get_root fs/btrfs/ctree.c:1665 [inline]
btrfs_search_slot+0x495/0x2fe0 fs/btrfs/ctree.c:1985

btrfs_update_root+0xf0/0xc60 fs/btrfs/root-tree.c:132
commit_fs_roots+0x4d3/0x710 fs/btrfs/transaction.c:1441
btrfs_commit_transaction+0x147f/0x3760 fs/btrfs/transaction.c:2353
sync_filesystem+0x1bc/0x220 fs/sync.c:66
generic_shutdown_super+0x6b/0x310 fs/super.c:474
kill_anon_super+0x36/0x60 fs/super.c:1086
btrfs_kill_super+0x3d/0x50 fs/btrfs/super.c:2441
deactivate_locked_super+0xa7/0xf0 fs/super.c:332
cleanup_mnt+0x494/0x520 fs/namespace.c:1186
task_work_run+0x243/0x300 kernel/task_work.c:179
ptrace_notify+0x29a/0x340 kernel/signal.c:2354
ptrace_report_syscall include/linux/ptrace.h:420 [inline]
ptrace_report_syscall_exit include/linux/ptrace.h:482 [inline]
syscall_exit_work+0x8c/0xe0 kernel/entry/common.c:251
syscall_exit_to_user_mode_prepare+0x63/0xc0 kernel/entry/common.c:278
__syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
syscall_exit_to_user_mode+0xa/0x60 kernel/entry/common.c:296
do_syscall_64+0x49/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #3 (&fs_info->reloc_mutex){+.+.}-{3:3}:
lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5668
__mutex_lock_common+0x1bd/0x26e0 kernel/locking/mutex.c:603
__mutex_lock kernel/locking/mutex.c:747 [inline]
mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:799
btrfs_record_root_in_trans+0x153/0x180 fs/btrfs/transaction.c:484
start_transaction+0x3af/0x1180 fs/btrfs/transaction.c:721

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_open fs/open.c:1334 [inline]
__se_sys_open fs/open.c:1330 [inline]
__x64_sys_open+0x221/0x270 fs/open.c:1330

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_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_open fs/open.c:1334 [inline]
__se_sys_open fs/open.c:1330 [inline]
__x64_sys_open+0x221/0x270 fs/open.c:1330

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

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5668
join_transaction+0x17a/0xe60 fs/btrfs/transaction.c:298
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_open fs/open.c:1334 [inline]
__se_sys_open fs/open.c:1330 [inline]
__x64_sys_open+0x221/0x270 fs/open.c:1330

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

-> #0 (sb_internal#2){.+.+}-{0:0}:
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
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1826 [inline]
sb_start_intwrite include/linux/fs.h:1948 [inline]
start_transaction+0x5cb/0x1180 fs/btrfs/transaction.c:652
btrfs_dirty_inode+0xcc/0x1c0 fs/btrfs/inode.c:6085
inode_update_time fs/inode.c:1871 [inline]
touch_atime+0x315/0x630 fs/inode.c:1944
file_accessed include/linux/fs.h:2521 [inline]
btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:2333
call_mmap include/linux/fs.h:2196 [inline]

mmap_region+0xfe6/0x1e20 mm/mmap.c:2625
do_mmap+0x8d9/0xf30 mm/mmap.c:1412

vm_mmap_pgoff+0x19e/0x2b0 mm/util.c:520
ksys_mmap_pgoff+0x48c/0x6d0 mm/mmap.c:1458
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:
sb_internal#2 --> btrfs-root-00 --> &mm->mmap_lock#2

Possible unsafe locking scenario:

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

*** DEADLOCK ***

2 locks held by syz-executor589/3733:
#0: ffff88807d23acd8 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
#0: ffff88807d23acd8 (&mm->mmap_lock#2){++++}-{3:3}, at: vm_mmap_pgoff+0x14d/0x2b0 mm/util.c:518
#1: ffff88807658c460 (sb_writers#9){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2521 [inline]
#1: ffff88807658c460 (sb_writers#9){.+.+}-{0:0}, at: btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:2333

stack backtrace:
CPU: 0 PID: 3733 Comm: syz-executor589 Not tainted 6.1.0-rc5-syzkaller-00008-ge01d50cbd6ee #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
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1826 [inline]
sb_start_intwrite include/linux/fs.h:1948 [inline]
start_transaction+0x5cb/0x1180 fs/btrfs/transaction.c:652
btrfs_dirty_inode+0xcc/0x1c0 fs/btrfs/inode.c:6085
inode_update_time fs/inode.c:1871 [inline]
touch_atime+0x315/0x630 fs/inode.c:1944
file_accessed include/linux/fs.h:2521 [inline]
btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:2333
call_mmap include/linux/fs.h:2196 [inline]

mmap_region+0xfe6/0x1e20 mm/mmap.c:2625
do_mmap+0x8d9/0xf30 mm/mmap.c:1412

vm_mmap_pgoff+0x19e/0x2b0 mm/util.c:520
ksys_mmap_pgoff+0x48c/0x6d0 mm/mmap.c:1458
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: 0033:0x7f714153d709
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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffda0941a38 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f7141585938 RCX: 00007f714153d709
RDX: 0000000000000001 RSI: 0000000000400000 RDI: 0000000020000000
RBP: 00007f7141585850 R08: 0000000000000006 R09: 0000000000000000
R10: 0000000000010012 R11: 0000000000000246 R12: 00007f7141585708
R13: 00007f71415856a0 R14: 00007ffda0941a80 R15: 0000000000000006
</TASK>

[Hillf Danton]

On 14 Nov 2022 18:40:41 -0800

> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: e01d50cbd6ee Merge tag 'vfio-v6.1-rc6' of https://github.c..
> git tree: upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=149ca515880000
> kernel config: https://syzkaller.appspot.com/x/.config?x=47b0b2ecc119b39f
> dashboard link: https://syzkaller.appspot.com/bug?extid=37edf86c9b60581e523f

> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=140c35d1880000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10df68e6880000

Release lock before copying to user.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git e01d50cbd6ee

--- x/fs/btrfs/ioctl.c
+++ y/fs/btrfs/ioctl.c
@@ -3194,6 +3194,8 @@ static int btrfs_ioctl_get_subvol_rootre
}

out:
+ btrfs_free_path(path);
+
if (!ret || ret == -EOVERFLOW) {
rootrefs->num_items = found;
/* update min_treeid for next search */
@@ -3205,7 +3207,6 @@ out:
}

kfree(rootrefs);
- btrfs_free_path(path);

return ret;
}
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+37edf8...@syzkaller.appspotmail.com

Tested on:

commit: e01d50cb Merge tag 'vfio-v6.1-rc6' of https://github.c..
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=15081dae880000

kernel config: https://syzkaller.appspot.com/x/.config?x=47b0b2ecc119b39f
dashboard link: https://syzkaller.appspot.com/bug?extid=37edf86c9b60581e523f

compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2

patch: https://syzkaller.appspot.com/x/patch.diff?x=110f46be880000

Note: testing is done by a robot and is best-effort only.

[syzbot]

syzbot suspects this issue was fixed by commit:

commit b740d806166979488e798e41743aaec051f2443f
Author: Josef Bacik <jo...@toxicpanda.com>
Date: Mon Nov 7 16:44:51 2022 +0000

btrfs: free btrfs_path before copying root refs to userspace

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10cf123e480000
start commit: 77c51ba552a1 Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=6f9416d398342c83
dashboard link: https://syzkaller.appspot.com/bug?extid=37edf86c9b60581e523f
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=148fcd31880000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=167bfb31880000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: btrfs: free btrfs_path before copying root refs to userspace

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.