[syzbot] possible deadlock in btrfs_join_transaction

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9500fc6e9e60 Merge branch 'for-next/core' into for-kernelci
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=173a95f9880000
kernel config: https://syzkaller.appspot.com/x/.config?x=b25c9f218686dd5e
dashboard link: https://syzkaller.appspot.com/bug?extid=6eb64eace626d6222d2a
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1363e60652f7/disk-9500fc6e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/fcc4da811bb6/vmlinux-9500fc6e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0b554298f1fa/Image-9500fc6e.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6eb64e...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.1.0-rc5-syzkaller-32269-g9500fc6e9e60 #0 Not tainted
------------------------------------------------------
syz-executor.4/30618 is trying to acquire lock:
ffff0000d3bca650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764

but task is already holding lock:
ffff0000d3bca558 (sb_pagefaults#2){.+.+}-{0:0}, at: do_page_mkwrite+0x74/0x288 mm/memory.c:2978

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (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+0xb4/0x6fc fs/btrfs/inode.c:8415
do_page_mkwrite+0x74/0x288 mm/memory.c:2978
do_shared_fault mm/memory.c:4619 [inline]
do_fault+0x274/0x550 mm/memory.c:4687
handle_pte_fault mm/memory.c:4955 [inline]
__handle_mm_fault mm/memory.c:5097 [inline]
handle_mm_fault+0x78c/0xa48 mm/memory.c:5218
__do_page_fault arch/arm64/mm/fault.c:512 [inline]
do_page_fault+0x428/0x79c arch/arm64/mm/fault.c:612
do_translation_fault+0x78/0x194 arch/arm64/mm/fault.c:695
do_mem_abort+0x54/0x130 arch/arm64/mm/fault.c:831
el0_da+0x70/0x16c arch/arm64/kernel/entry-common.c:515
el0t_64_sync_handler+0xcc/0xf0 arch/arm64/kernel/entry-common.c:658
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #4 (&mm->mmap_lock){++++}-{3:3}:
__might_fault+0x7c/0xb4 mm/memory.c:5646
_copy_to_user include/linux/uaccess.h:143 [inline]
copy_to_user include/linux/uaccess.h:169 [inline]
btrfs_ioctl_get_subvol_rootref+0x3a8/0x4bc fs/btrfs/ioctl.c:3203
btrfs_ioctl+0xa08/0xa64 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]
__arm64_sys_ioctl+0xd0/0x140 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #3 (btrfs-root-00){++++}-{3:3}:
down_read_nested+0x64/0x84 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+0x13c/0x1c0 fs/btrfs/locking.c:279
btrfs_search_slot_get_root+0x8c/0x374 fs/btrfs/ctree.c:1665
btrfs_search_slot+0x1dc/0x107c fs/btrfs/ctree.c:1985
btrfs_del_root+0x50/0xd0 fs/btrfs/root-tree.c:317
btrfs_clear_free_space_tree+0x268/0x49c fs/btrfs/free-space-tree.c:1273
btrfs_start_pre_rw_mount+0x128/0x380 fs/btrfs/disk-io.c:3210
open_ctree+0xb70/0xdc8 fs/btrfs/disk-io.c:3792
btrfs_fill_super+0xc0/0x174 fs/btrfs/super.c:1461
btrfs_mount_root+0x4a4/0x558 fs/btrfs/super.c:1829
legacy_get_tree+0x30/0x74 fs/fs_context.c:610
vfs_get_tree+0x40/0x140 fs/super.c:1531
fc_mount fs/namespace.c:1043 [inline]
vfs_kern_mount+0xe0/0x140 fs/namespace.c:1073
btrfs_mount+0x20c/0x5e8 fs/btrfs/super.c:1889
legacy_get_tree+0x30/0x74 fs/fs_context.c:610
vfs_get_tree+0x40/0x140 fs/super.c:1531
do_new_mount+0x1dc/0x4e4 fs/namespace.c:3040
path_mount+0x358/0x890 fs/namespace.c:3370
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount fs/namespace.c:3568 [inline]
__arm64_sys_mount+0x2c4/0x3c4 fs/namespace.c:3568
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
join_transaction+0x10c/0x65c fs/btrfs/transaction.c:299
start_transaction+0x460/0x944 fs/btrfs/transaction.c:658
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764
btrfs_commit_super+0x64/0xa0 fs/btrfs/disk-io.c:4496
close_ctree+0x1dc/0x60c fs/btrfs/disk-io.c:4653
btrfs_put_super+0x20/0x30 fs/btrfs/super.c:394
generic_shutdown_super+0x94/0x198 fs/super.c:492
kill_anon_super+0x24/0x44 fs/super.c:1086
btrfs_kill_super+0x24/0x3c fs/btrfs/super.c:2441
deactivate_locked_super+0x70/0xe8 fs/super.c:332
deactivate_super+0xd0/0xd4 fs/super.c:363
cleanup_mnt+0x184/0x1c0 fs/namespace.c:1186
__cleanup_mnt+0x20/0x30 fs/namespace.c:1193
task_work_run+0x100/0x148 kernel/task_work.c:179
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
do_notify_resume+0x174/0x1f0 arch/arm64/kernel/signal.c:1127
prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
el0_svc+0x9c/0x150 arch/arm64/kernel/entry-common.c:638
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
join_transaction+0xe8/0x65c fs/btrfs/transaction.c:298
start_transaction+0x460/0x944 fs/btrfs/transaction.c:658
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764
btrfs_commit_super+0x64/0xa0 fs/btrfs/disk-io.c:4496
close_ctree+0x1dc/0x60c fs/btrfs/disk-io.c:4653
btrfs_put_super+0x20/0x30 fs/btrfs/super.c:394
generic_shutdown_super+0x94/0x198 fs/super.c:492
kill_anon_super+0x24/0x44 fs/super.c:1086
btrfs_kill_super+0x24/0x3c fs/btrfs/super.c:2441
deactivate_locked_super+0x70/0xe8 fs/super.c:332
deactivate_super+0xd0/0xd4 fs/super.c:363
cleanup_mnt+0x184/0x1c0 fs/namespace.c:1186
__cleanup_mnt+0x20/0x30 fs/namespace.c:1193
task_work_run+0x100/0x148 kernel/task_work.c:179
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
do_notify_resume+0x174/0x1f0 arch/arm64/kernel/signal.c:1127
prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
el0_svc+0x9c/0x150 arch/arm64/kernel/entry-common.c:638
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #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 kernel/locking/lockdep.c:3831 [inline]
__lock_acquire+0x1530/0x3084 kernel/locking/lockdep.c:5055
lock_acquire+0x100/0x1f8 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+0x360/0x944 fs/btrfs/transaction.c:652
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764
btrfs_dirty_inode+0x4c/0x13c fs/btrfs/inode.c:6085
btrfs_update_time+0x120/0x138 fs/btrfs/inode.c:6127
inode_update_time fs/inode.c:1871 [inline]
__file_update_time fs/inode.c:2088 [inline]
file_update_time+0x194/0x2c0 fs/inode.c:2119
btrfs_page_mkwrite+0x204/0x6fc fs/btrfs/inode.c:8431
do_page_mkwrite+0x74/0x288 mm/memory.c:2978
do_shared_fault mm/memory.c:4619 [inline]
do_fault+0x274/0x550 mm/memory.c:4687
handle_pte_fault mm/memory.c:4955 [inline]
__handle_mm_fault mm/memory.c:5097 [inline]
handle_mm_fault+0x78c/0xa48 mm/memory.c:5218
__do_page_fault arch/arm64/mm/fault.c:512 [inline]
do_page_fault+0x428/0x79c arch/arm64/mm/fault.c:612
do_translation_fault+0x78/0x194 arch/arm64/mm/fault.c:695
do_mem_abort+0x54/0x130 arch/arm64/mm/fault.c:831
el0_da+0x70/0x16c arch/arm64/kernel/entry-common.c:515
el0t_64_sync_handler+0xcc/0xf0 arch/arm64/kernel/entry-common.c:658
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

other info that might help us debug this:

Chain exists of:
sb_internal#2 --> &mm->mmap_lock --> sb_pagefaults#2

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sb_pagefaults#2);
lock(&mm->mmap_lock);
lock(sb_pagefaults#2);
lock(sb_internal#2);

*** DEADLOCK ***

2 locks held by syz-executor.4/30618:
#0: ffff0000c0e15648 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_lock include/linux/mmap_lock.h:117 [inline]
#0: ffff0000c0e15648 (&mm->mmap_lock){++++}-{3:3}, at: do_page_fault+0x3c8/0x79c arch/arm64/mm/fault.c:597
#1: ffff0000d3bca558 (sb_pagefaults#2){.+.+}-{0:0}, at: do_page_mkwrite+0x74/0x288 mm/memory.c:2978

stack backtrace:
CPU: 0 PID: 30618 Comm: syz-executor.4 Not tainted 6.1.0-rc5-syzkaller-32269-g9500fc6e9e60 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/30/2022
Call trace:
dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:156
show_stack+0x2c/0x54 arch/arm64/kernel/stacktrace.c:163
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x104/0x16c lib/dump_stack.c:106
dump_stack+0x1c/0x58 lib/dump_stack.c:113
print_circular_bug+0x2c4/0x2c8 kernel/locking/lockdep.c:2055
check_noncircular+0x14c/0x154 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+0x1530/0x3084 kernel/locking/lockdep.c:5055
lock_acquire+0x100/0x1f8 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+0x360/0x944 fs/btrfs/transaction.c:652
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764
btrfs_dirty_inode+0x4c/0x13c fs/btrfs/inode.c:6085
btrfs_update_time+0x120/0x138 fs/btrfs/inode.c:6127
inode_update_time fs/inode.c:1871 [inline]
__file_update_time fs/inode.c:2088 [inline]
file_update_time+0x194/0x2c0 fs/inode.c:2119
btrfs_page_mkwrite+0x204/0x6fc fs/btrfs/inode.c:8431
do_page_mkwrite+0x74/0x288 mm/memory.c:2978
do_shared_fault mm/memory.c:4619 [inline]
do_fault+0x274/0x550 mm/memory.c:4687
handle_pte_fault mm/memory.c:4955 [inline]
__handle_mm_fault mm/memory.c:5097 [inline]
handle_mm_fault+0x78c/0xa48 mm/memory.c:5218
__do_page_fault arch/arm64/mm/fault.c:512 [inline]
do_page_fault+0x428/0x79c arch/arm64/mm/fault.c:612
do_translation_fault+0x78/0x194 arch/arm64/mm/fault.c:695
do_mem_abort+0x54/0x130 arch/arm64/mm/fault.c:831
el0_da+0x70/0x16c arch/arm64/kernel/entry-common.c:515
el0t_64_sync_handler+0xcc/0xf0 arch/arm64/kernel/entry-common.c:658
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 6d464646530f Merge branch 'for-next/core' into for-kernelci

git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci

console output: https://syzkaller.appspot.com/x/log.txt?x=111da6a1880000
kernel config: https://syzkaller.appspot.com/x/.config?x=54b747d981acc7b7

dashboard link: https://syzkaller.appspot.com/bug?extid=6eb64eace626d6222d2a
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12b284bd880000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11346825880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d75f5f77b3a3/disk-6d464646.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9382f86e4d95/vmlinux-6d464646.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cf2b5f0d51dd/Image-6d464646.gz.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/6232bad1430d/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6eb64e...@syzkaller.appspotmail.com

BTRFS info (device loop0): using sha256 (sha256-ce) checksum algorithm
BTRFS info (device loop0): using free space tree
BTRFS info (device loop0): enabling ssd optimizations

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

6.1.0-rc6-syzkaller-32662-g6d464646530f #0 Not tainted
------------------------------------------------------
syz-executor220/3357 is trying to acquire lock:
ffff0000c9b90650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764

but task is already holding lock:

ffff0000ca11fb08 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
ffff0000ca11fb08 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0xa0/0x1d0 mm/util.c:518

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

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

__might_fault+0x7c/0xb4 mm/memory.c:5646
_copy_to_user include/linux/uaccess.h:143 [inline]
copy_to_user include/linux/uaccess.h:169 [inline]
btrfs_ioctl_get_subvol_rootref+0x3a8/0x4bc fs/btrfs/ioctl.c:3203
btrfs_ioctl+0xa08/0xa64 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]
__arm64_sys_ioctl+0xd0/0x140 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #4 (btrfs-root-00){++++}-{3:3}:

down_read_nested+0x64/0x84 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+0x13c/0x1c0 fs/btrfs/locking.c:279
btrfs_search_slot_get_root+0x8c/0x374 fs/btrfs/ctree.c:1665
btrfs_search_slot+0x1dc/0x107c fs/btrfs/ctree.c:1985

btrfs_update_root+0x6c/0x5a4 fs/btrfs/root-tree.c:132
commit_fs_roots+0x1f0/0x33c fs/btrfs/transaction.c:1441
btrfs_commit_transaction+0xa94/0x1574 fs/btrfs/transaction.c:2353
btrfs_sync_fs+0x2b8/0x48c fs/btrfs/super.c:1527
sync_filesystem+0xe0/0x134 fs/sync.c:66
generic_shutdown_super+0x38/0x198 fs/super.c:474

kill_anon_super+0x24/0x44 fs/super.c:1086
btrfs_kill_super+0x24/0x3c fs/btrfs/super.c:2441
deactivate_locked_super+0x70/0xe8 fs/super.c:332
deactivate_super+0xd0/0xd4 fs/super.c:363
cleanup_mnt+0x184/0x1c0 fs/namespace.c:1186
__cleanup_mnt+0x20/0x30 fs/namespace.c:1193
task_work_run+0x100/0x148 kernel/task_work.c:179
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
do_notify_resume+0x174/0x1f0 arch/arm64/kernel/signal.c:1127
prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
el0_svc+0x9c/0x150 arch/arm64/kernel/entry-common.c:638
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #3 (&fs_info->reloc_mutex){+.+.}-{3:3}:
__mutex_lock_common+0xd4/0xca8 kernel/locking/mutex.c:603
__mutex_lock kernel/locking/mutex.c:747 [inline]
mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
btrfs_record_root_in_trans fs/btrfs/transaction.c:484 [inline]
start_transaction+0x248/0x944 fs/btrfs/transaction.c:721
btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:750
btrfs_create_common+0xf0/0x1b4 fs/btrfs/inode.c:6633
btrfs_create+0x8c/0xb0 fs/btrfs/inode.c:6679
lookup_open fs/namei.c:3413 [inline]
open_last_lookups fs/namei.c:3481 [inline]
path_openat+0x804/0x11c4 fs/namei.c:3710
do_filp_open+0xdc/0x1b8 fs/namei.c:3740
do_sys_openat2+0xb8/0x22c 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]
__arm64_sys_openat+0xb0/0xe0 fs/open.c:1337

__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
join_transaction+0x10c/0x65c fs/btrfs/transaction.c:299
start_transaction+0x460/0x944 fs/btrfs/transaction.c:658

btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:750
btrfs_create_common+0xf0/0x1b4 fs/btrfs/inode.c:6633
btrfs_create+0x8c/0xb0 fs/btrfs/inode.c:6679
lookup_open fs/namei.c:3413 [inline]
open_last_lookups fs/namei.c:3481 [inline]
path_openat+0x804/0x11c4 fs/namei.c:3710
do_filp_open+0xdc/0x1b8 fs/namei.c:3740
do_sys_openat2+0xb8/0x22c 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]
__arm64_sys_openat+0xb0/0xe0 fs/open.c:1337

__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
join_transaction+0xe8/0x65c fs/btrfs/transaction.c:298
start_transaction+0x460/0x944 fs/btrfs/transaction.c:658

btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:750
btrfs_create_common+0xf0/0x1b4 fs/btrfs/inode.c:6633
btrfs_create+0x8c/0xb0 fs/btrfs/inode.c:6679
lookup_open fs/namei.c:3413 [inline]
open_last_lookups fs/namei.c:3481 [inline]
path_openat+0x804/0x11c4 fs/namei.c:3710
do_filp_open+0xdc/0x1b8 fs/namei.c:3740
do_sys_openat2+0xb8/0x22c 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]
__arm64_sys_openat+0xb0/0xe0 fs/open.c:1337

__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #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 kernel/locking/lockdep.c:3831 [inline]
__lock_acquire+0x1530/0x3084 kernel/locking/lockdep.c:5055
lock_acquire+0x100/0x1f8 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+0x360/0x944 fs/btrfs/transaction.c:652
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764
btrfs_dirty_inode+0x4c/0x13c fs/btrfs/inode.c:6085
btrfs_update_time+0x120/0x138 fs/btrfs/inode.c:6127
inode_update_time fs/inode.c:1871 [inline]

touch_atime+0x1f0/0x4a8 fs/inode.c:1944
file_accessed include/linux/fs.h:2521 [inline]
btrfs_file_mmap+0x50/0x88 fs/btrfs/file.c:2333
call_mmap include/linux/fs.h:2196 [inline]
mmap_region+0x8a0/0x1064 mm/mmap.c:2625
do_mmap+0x6e8/0xa30 mm/mmap.c:1412
vm_mmap_pgoff+0xe8/0x1d0 mm/util.c:520
ksys_mmap_pgoff+0x1cc/0x278 mm/mmap.c:1458
__do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
__se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
__arm64_sys_mmap+0x58/0x6c arch/arm64/kernel/sys.c:21

__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

other info that might help us debug this:

Chain exists of:

sb_internal#2 --> btrfs-root-00 --> &mm->mmap_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----

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

*** DEADLOCK ***

2 locks held by syz-executor220/3357:
#0: ffff0000ca11fb08 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
#0: ffff0000ca11fb08 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0xa0/0x1d0 mm/util.c:518
#1: ffff0000c9b90460 (sb_writers#8){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2521 [inline]
#1: ffff0000c9b90460 (sb_writers#8){.+.+}-{0:0}, at: btrfs_file_mmap+0x50/0x88 fs/btrfs/file.c:2333

stack backtrace:
CPU: 1 PID: 3357 Comm: syz-executor220 Not tainted 6.1.0-rc6-syzkaller-32662-g6d464646530f #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/30/2022
Call trace:
dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:156
show_stack+0x2c/0x54 arch/arm64/kernel/stacktrace.c:163
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x104/0x16c lib/dump_stack.c:106
dump_stack+0x1c/0x58 lib/dump_stack.c:113
print_circular_bug+0x2c4/0x2c8 kernel/locking/lockdep.c:2055
check_noncircular+0x14c/0x154 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+0x1530/0x3084 kernel/locking/lockdep.c:5055
lock_acquire+0x100/0x1f8 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+0x360/0x944 fs/btrfs/transaction.c:652
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764
btrfs_dirty_inode+0x4c/0x13c fs/btrfs/inode.c:6085
btrfs_update_time+0x120/0x138 fs/btrfs/inode.c:6127
inode_update_time fs/inode.c:1871 [inline]

touch_atime+0x1f0/0x4a8 fs/inode.c:1944
file_accessed include/linux/fs.h:2521 [inline]
btrfs_file_mmap+0x50/0x88 fs/btrfs/file.c:2333
call_mmap include/linux/fs.h:2196 [inline]
mmap_region+0x8a0/0x1064 mm/mmap.c:2625
do_mmap+0x6e8/0xa30 mm/mmap.c:1412
vm_mmap_pgoff+0xe8/0x1d0 mm/util.c:520
ksys_mmap_pgoff+0x1cc/0x278 mm/mmap.c:1458
__do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
__se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
__arm64_sys_mmap+0x58/0x6c arch/arm64/kernel/sys.c:21

[Hillf Danton]

On 29 Nov 2022 03:54:50 -0800

> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 6d464646530f Merge branch 'for-next/core' into for-kernelci
> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci

> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11346825880000

Copy to user after releasing lock to break the lock chain.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git 6d464646530f

--- a/fs/btrfs/ioctl.c
+++ b/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+6eb64e...@syzkaller.appspotmail.com

Tested on:

commit: 6d464646 Merge branch 'for-next/core' into for-kernelci
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1082bce3880000

kernel config: https://syzkaller.appspot.com/x/.config?x=54b747d981acc7b7
dashboard link: https://syzkaller.appspot.com/bug?extid=6eb64eace626d6222d2a
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64

patch: https://syzkaller.appspot.com/x/patch.diff?x=15ac3d03880000

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

[syzbot]

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