[v6.1] possible deadlock in ocfs2_lock_refcount_tree (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 128a674368bf Linux 6.1.171
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1052f1ce580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b1adc0bfde2d8a4a
dashboard link: https://syzkaller.appspot.com/bug?extid=1698551c43bd8a774aa5
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d82b9cc52945/disk-128a6743.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/711be855b9d4/vmlinux-128a6743.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dbe168ed61d6/Image-128a6743.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+169855...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.457/5854 is trying to acquire lock:
ffff0000d574d898 (&new->rf_sem){+.+.}-{3:3}, at: __ocfs2_lock_refcount_tree fs/ocfs2/refcounttree.c:428 [inline]
ffff0000d574d898 (&new->rf_sem){+.+.}-{3:3}, at: ocfs2_lock_refcount_tree+0x178/0x93c fs/ocfs2/refcounttree.c:463

but task is already holding lock:
ffff0000f52d8660 (&ocfs2_file_ip_alloc_sem_key){++++}-{3:3}, at: ocfs2_page_mkwrite+0x328/0xc00 fs/ocfs2/mmap.c:142

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&ocfs2_file_ip_alloc_sem_key){++++}-{3:3}:
down_read+0x64/0x300 kernel/locking/rwsem.c:1520
ocfs2_read_virt_blocks+0x238/0x8f0 fs/ocfs2/extent_map.c:984
ocfs2_read_dir_block fs/ocfs2/dir.c:508 [inline]
ocfs2_find_entry_el fs/ocfs2/dir.c:715 [inline]
ocfs2_find_entry+0x2e4/0x1d6c fs/ocfs2/dir.c:1091
ocfs2_find_files_on_disk+0x128/0x40c fs/ocfs2/dir.c:1995
ocfs2_lookup_ino_from_name+0x60/0x114 fs/ocfs2/dir.c:2017
_ocfs2_get_system_file_inode fs/ocfs2/sysfile.c:136 [inline]
ocfs2_get_system_file_inode+0x2c0/0x690 fs/ocfs2/sysfile.c:112
ocfs2_init_global_system_inodes+0x2a0/0x5c8 fs/ocfs2/super.c:457
ocfs2_initialize_super fs/ocfs2/super.c:2253 [inline]
ocfs2_fill_super+0x2408/0x436c fs/ocfs2/super.c:994
mount_bdev+0x264/0x358 fs/super.c:1443
ocfs2_mount+0x44/0x58 fs/ocfs2/super.c:1186
legacy_get_tree+0xd4/0x16c fs/fs_context.c:632
vfs_get_tree+0x90/0x274 fs/super.c:1573
do_new_mount+0x228/0x810 fs/namespace.c:3078
path_mount+0x5bc/0xe80 fs/namespace.c:3408
do_mount fs/namespace.c:3421 [inline]
__do_sys_mount fs/namespace.c:3629 [inline]
__se_sys_mount fs/namespace.c:3606 [inline]
__arm64_sys_mount+0x49c/0x59c fs/namespace.c:3606
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #1 (&osb->system_file_mutex){+.+.}-{3:3}:
__mutex_lock_common+0x190/0x1f60 kernel/locking/mutex.c:603
__mutex_lock kernel/locking/mutex.c:747 [inline]
mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
ocfs2_get_system_file_inode+0x158/0x690 fs/ocfs2/sysfile.c:101
ocfs2_reserve_suballoc_bits+0xfc/0x3c80 fs/ocfs2/suballoc.c:776
ocfs2_reserve_new_metadata_blocks+0x36c/0x830 fs/ocfs2/suballoc.c:978
ocfs2_add_refcount_flag+0x364/0xf00 fs/ocfs2/refcounttree.c:3683
ocfs2_reflink_remap_extent fs/ocfs2/refcounttree.c:4563 [inline]
ocfs2_reflink_remap_blocks+0xa98/0x15a8 fs/ocfs2/refcounttree.c:4690
ocfs2_remap_file_range+0x3f8/0x64c fs/ocfs2/file.c:2703
vfs_copy_file_range+0xb38/0x11c8 fs/read_write.c:1518
__do_sys_copy_file_range fs/read_write.c:1596 [inline]
__se_sys_copy_file_range fs/read_write.c:1559 [inline]
__arm64_sys_copy_file_range+0x500/0x828 fs/read_write.c:1559
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #0 (&new->rf_sem){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3090 [inline]
check_prevs_add kernel/locking/lockdep.c:3209 [inline]
validate_chain kernel/locking/lockdep.c:3825 [inline]
__lock_acquire+0x2880/0x6800 kernel/locking/lockdep.c:5049
lock_acquire+0x20c/0x63c kernel/locking/lockdep.c:5662
down_write+0x5c/0x88 kernel/locking/rwsem.c:1573
__ocfs2_lock_refcount_tree fs/ocfs2/refcounttree.c:428 [inline]
ocfs2_lock_refcount_tree+0x178/0x93c fs/ocfs2/refcounttree.c:463
ocfs2_refcount_cow_hunk fs/ocfs2/refcounttree.c:3415 [inline]
ocfs2_refcount_cow+0x4a4/0xbf4 fs/ocfs2/refcounttree.c:3476
ocfs2_write_begin_nolock+0xe50/0x3a44 fs/ocfs2/aops.c:1701
__ocfs2_page_mkwrite fs/ocfs2/mmap.c:93 [inline]
ocfs2_page_mkwrite+0x5b0/0xc00 fs/ocfs2/mmap.c:144
do_page_mkwrite+0x13c/0x358 mm/memory.c:3009
wp_page_shared+0x148/0x540 mm/memory.c:3358
do_wp_page+0xca0/0xeec mm/memory.c:3508
handle_pte_fault mm/memory.c:5047 [inline]
__handle_mm_fault mm/memory.c:5171 [inline]
handle_mm_fault+0x1514/0x2fb0 mm/memory.c:5292
__do_page_fault arch/arm64/mm/fault.c:499 [inline]
do_page_fault+0x310/0x98c arch/arm64/mm/fault.c:583
do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:804
el0_da+0x70/0x144 arch/arm64/kernel/entry-common.c:515
el0t_64_sync_handler+0x90/0xf0 arch/arm64/kernel/entry-common.c:658
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

other info that might help us debug this:

Chain exists of:
&new->rf_sem --> &osb->system_file_mutex --> &ocfs2_file_ip_alloc_sem_key

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&ocfs2_file_ip_alloc_sem_key);
lock(&osb->system_file_mutex);
lock(&ocfs2_file_ip_alloc_sem_key);
lock(&new->rf_sem);

*** DEADLOCK ***

3 locks held by syz.3.457/5854:
#0: ffff0000dc8d1948 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline]
#0: ffff0000dc8d1948 (&mm->mmap_lock){++++}-{3:3}, at: get_mmap_lock_carefully mm/memory.c:5320 [inline]
#0: ffff0000dc8d1948 (&mm->mmap_lock){++++}-{3:3}, at: lock_mm_and_find_vma+0x38/0x2e0 mm/memory.c:5382
#1: ffff0000daa1c558 (sb_pagefaults#5){.+.+}-{0:0}, at: do_page_mkwrite+0x13c/0x358 mm/memory.c:3009
#2: ffff0000f52d8660 (&ocfs2_file_ip_alloc_sem_key){++++}-{3:3}, at: ocfs2_page_mkwrite+0x328/0xc00 fs/ocfs2/mmap.c:142

stack backtrace:
CPU: 0 PID: 5854 Comm: syz.3.457 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call trace:
dump_backtrace+0x1c0/0x1ec arch/arm64/kernel/stacktrace.c:158
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
__dump_stack+0x30/0x40 lib/dump_stack.c:88
dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
dump_stack+0x1c/0x5c lib/dump_stack.c:113
print_circular_bug+0x148/0x1b0 kernel/locking/lockdep.c:2048
check_noncircular+0x264/0x2f8 kernel/locking/lockdep.c:2170
check_prev_add kernel/locking/lockdep.c:3090 [inline]
check_prevs_add kernel/locking/lockdep.c:3209 [inline]
validate_chain kernel/locking/lockdep.c:3825 [inline]
__lock_acquire+0x2880/0x6800 kernel/locking/lockdep.c:5049
lock_acquire+0x20c/0x63c kernel/locking/lockdep.c:5662
down_write+0x5c/0x88 kernel/locking/rwsem.c:1573
__ocfs2_lock_refcount_tree fs/ocfs2/refcounttree.c:428 [inline]
ocfs2_lock_refcount_tree+0x178/0x93c fs/ocfs2/refcounttree.c:463
ocfs2_refcount_cow_hunk fs/ocfs2/refcounttree.c:3415 [inline]
ocfs2_refcount_cow+0x4a4/0xbf4 fs/ocfs2/refcounttree.c:3476
ocfs2_write_begin_nolock+0xe50/0x3a44 fs/ocfs2/aops.c:1701
__ocfs2_page_mkwrite fs/ocfs2/mmap.c:93 [inline]
ocfs2_page_mkwrite+0x5b0/0xc00 fs/ocfs2/mmap.c:144
do_page_mkwrite+0x13c/0x358 mm/memory.c:3009
wp_page_shared+0x148/0x540 mm/memory.c:3358
do_wp_page+0xca0/0xeec mm/memory.c:3508
handle_pte_fault mm/memory.c:5047 [inline]
__handle_mm_fault mm/memory.c:5171 [inline]
handle_mm_fault+0x1514/0x2fb0 mm/memory.c:5292
__do_page_fault arch/arm64/mm/fault.c:499 [inline]
do_page_fault+0x310/0x98c arch/arm64/mm/fault.c:583
do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:804
el0_da+0x70/0x144 arch/arm64/kernel/entry-common.c:515
el0t_64_sync_handler+0x90/0xf0 arch/arm64/kernel/entry-common.c:658
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585


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