[PATCH 6.12 204/567] f2fs: fix to avoid potential deadlock

Greg Kroah-Hartman
2026-01-06T17:25:35Z

From: Chao Yu <chao@kernel.org>

commit ca8b201f28547e28343a6f00a6e91fa8c09572fe upstream.

As Jiaming Zhang and syzbot reported, there is potential deadlock in
f2fs as below:

Chain exists of:
&sbi->cp_rwsem --> fs_reclaim --> sb_internal#2

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(sb_internal#2);
lock(fs_reclaim);
lock(sb_internal#2);
rlock(&sbi->cp_rwsem);

*** DEADLOCK ***

3 locks held by kswapd0/73:
#0: ffffffff8e247a40 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:7015 [inline]
#0: ffffffff8e247a40 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0x951/0x2800 mm/vmscan.c:7389
#1: ffff8880118400e0 (&type->s_umount_key#50){.+.+}-{4:4}, at: super_trylock_shared fs/super.c:562 [inline]
#1: ffff8880118400e0 (&type->s_umount_key#50){.+.+}-{4:4}, at: super_cache_scan+0x91/0x4b0 fs/super.c:197
#2: ffff888011840610 (sb_internal#2){.+.+}-{0:0}, at: f2fs_evict_inode+0x8d9/0x1b60 fs/f2fs/inode.c:890

stack backtrace:
CPU: 0 UID: 0 PID: 73 Comm: kswapd0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537
f2fs_down_read fs/f2fs/f2fs.h:2278 [inline]
f2fs_lock_op fs/f2fs/f2fs.h:2357 [inline]
f2fs_do_truncate_blocks+0x21c/0x10c0 fs/f2fs/file.c:791
f2fs_truncate_blocks+0x10a/0x300 fs/f2fs/file.c:867
f2fs_truncate+0x489/0x7c0 fs/f2fs/file.c:925
f2fs_evict_inode+0x9f2/0x1b60 fs/f2fs/inode.c:897
evict+0x504/0x9c0 fs/inode.c:810
f2fs_evict_inode+0x1dc/0x1b60 fs/f2fs/inode.c:853
evict+0x504/0x9c0 fs/inode.c:810
dispose_list fs/inode.c:852 [inline]
prune_icache_sb+0x21b/0x2c0 fs/inode.c:1000
super_cache_scan+0x39b/0x4b0 fs/super.c:224
do_shrink_slab+0x6ef/0x1110 mm/shrinker.c:437
shrink_slab_memcg mm/shrinker.c:550 [inline]
shrink_slab+0x7ef/0x10d0 mm/shrinker.c:628
shrink_one+0x28a/0x7c0 mm/vmscan.c:4955
shrink_many mm/vmscan.c:5016 [inline]
lru_gen_shrink_node mm/vmscan.c:5094 [inline]
shrink_node+0x315d/0x3780 mm/vmscan.c:6081
kswapd_shrink_node mm/vmscan.c:6941 [inline]
balance_pgdat mm/vmscan.c:7124 [inline]
kswapd+0x147c/0x2800 mm/vmscan.c:7389
kthread+0x70e/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

The root cause is deadlock among four locks as below:

kswapd
- fs_reclaim --- Lock A
- shrink_one
- evict
- f2fs_evict_inode
- sb_start_intwrite --- Lock B

- iput
- evict
- f2fs_evict_inode
- sb_start_intwrite --- Lock B
- f2fs_truncate
- f2fs_truncate_blocks
- f2fs_do_truncate_blocks
- f2fs_lock_op --- Lock C

ioctl
- f2fs_ioc_commit_atomic_write
- f2fs_lock_op --- Lock C
- __f2fs_commit_atomic_write
- __replace_atomic_write_block
- f2fs_get_dnode_of_data
- __get_node_folio
- f2fs_check_nid_range
- f2fs_handle_error
- f2fs_record_errors
- f2fs_down_write --- Lock D

open
- do_open
- do_truncate
- security_inode_need_killpriv
- f2fs_getxattr
- lookup_all_xattrs
- f2fs_handle_error
- f2fs_record_errors
- f2fs_down_write --- Lock D
- f2fs_commit_super
- read_mapping_folio
- filemap_alloc_folio_noprof
- prepare_alloc_pages
- fs_reclaim_acquire --- Lock A

In order to avoid such deadlock, we need to avoid grabbing sb_lock in
f2fs_handle_error(), so, let's use asynchronous method instead:
- remove f2fs_handle_error() implementation
- rename f2fs_handle_error_async() to f2fs_handle_error()
- spread f2fs_handle_error()

Fixes: 95fa90c9e5a7 ("f2fs: support recording errors into superblock")
Cc: stable@kernel.org
Reported-by: syzbot+14b90e1156b9f6fc1266@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-f2fs-devel/68eae49b.050a0220.ac43.0001.GAE@google.com
Reported-by: Jiaming Zhang <r772577952@gmail.com>
Closes: https://lore.kernel.org/lkml/CANypQFa-Gy9sD-N35o3PC+FystOWkNuN8pv6S75HLT0ga-Tzgw@mail.gmail.com
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/f2fs/compress.c | 5 +----
fs/f2fs/f2fs.h | 1 -
fs/f2fs/super.c | 41 -----------------------------------------
3 files changed, 1 insertion(+), 46 deletions(-)

--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -757,10 +757,7 @@ void f2fs_decompress_cluster(struct deco
ret = -EFSCORRUPTED;

/* Avoid f2fs_commit_super in irq context */
- if (!in_task)
- f2fs_handle_error_async(sbi, ERROR_FAIL_DECOMPRESSION);
- else
- f2fs_handle_error(sbi, ERROR_FAIL_DECOMPRESSION);
+ f2fs_handle_error(sbi, ERROR_FAIL_DECOMPRESSION);
goto out_release;
}

--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -3694,7 +3694,6 @@ void f2fs_quota_off_umount(struct super_
void f2fs_save_errors(struct f2fs_sb_info *sbi, unsigned char flag);
void f2fs_handle_critical_error(struct f2fs_sb_info *sbi, unsigned char reason);
void f2fs_handle_error(struct f2fs_sb_info *sbi, unsigned char error);
-void f2fs_handle_error_async(struct f2fs_sb_info *sbi, unsigned char error);
int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover);
int f2fs_sync_fs(struct super_block *sb, int sync);
int f2fs_sanity_check_ckpt(struct f2fs_sb_info *sbi);
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4143,50 +4143,9 @@ void f2fs_save_errors(struct f2fs_sb_inf
spin_unlock_irqrestore(&sbi->error_lock, flags);
}

-static bool f2fs_update_errors(struct f2fs_sb_info *sbi)
-{
- unsigned long flags;
- bool need_update = false;
-
- spin_lock_irqsave(&sbi->error_lock, flags);
- if (sbi->error_dirty) {
- memcpy(F2FS_RAW_SUPER(sbi)->s_errors, sbi->errors,
- MAX_F2FS_ERRORS);
- sbi->error_dirty = false;
- need_update = true;
- }
- spin_unlock_irqrestore(&sbi->error_lock, flags);
-
- return need_update;
-}
-
-static void f2fs_record_errors(struct f2fs_sb_info *sbi, unsigned char error)
-{
- int err;
-
- f2fs_down_write(&sbi->sb_lock);
-
- if (!f2fs_update_errors(sbi))
- goto out_unlock;
-
- err = f2fs_commit_super(sbi, false);
- if (err)
- f2fs_err_ratelimited(sbi,
- "f2fs_commit_super fails to record errors:%u, err:%d",
- error, err);
-out_unlock:
- f2fs_up_write(&sbi->sb_lock);
-}
-
void f2fs_handle_error(struct f2fs_sb_info *sbi, unsigned char error)
{
f2fs_save_errors(sbi, error);
- f2fs_record_errors(sbi, error);
-}
-
-void f2fs_handle_error_async(struct f2fs_sb_info *sbi, unsigned char error)
-{
- f2fs_save_errors(sbi, error);

if (!sbi->error_dirty)
return;