Re: [syzbot] [xfs?] possible deadlock in xfs_buf_find_insert

syzbot
2025-02-02T00:53:24Z

syzbot has found a reproducer for the following issue on:

HEAD commit: 69b8923f5003 Merge tag 'for-linus-6.14-ofs4' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1361fddf980000
kernel config: https://syzkaller.appspot.com/x/.config?x=57ab43c279fa614d
dashboard link: https://syzkaller.appspot.com/bug?extid=acb56162aef712929d3f
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=174cd5f8580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=162e2d18580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ea84ac864e92/disk-69b8923f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6a465997b4e0/vmlinux-69b8923f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d72b67b2bd15/bzImage-69b8923f.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/2d5b00530bed/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+acb56162aef712929d3f@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.13.0-syzkaller-09793-g69b8923f5003 #0 Not tainted
------------------------------------------------------
syz-executor278/5867 is trying to acquire lock:
ffff8880787b0da0 (&bp->b_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff8880787b0da0 (&bp->b_lock){+.+.}-{3:3}, at: xfs_buf_try_hold fs/xfs/xfs_buf.c:578 [inline]
ffff8880787b0da0 (&bp->b_lock){+.+.}-{3:3}, at: xfs_buf_find_insert+0x1123/0x1610 fs/xfs/xfs_buf.c:663

but task is already holding lock:
ffff888026f07980 (&bch->bc_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff888026f07980 (&bch->bc_lock){+.+.}-{3:3}, at: xfs_buf_find_insert+0x3da/0x1610 fs/xfs/xfs_buf.c:655

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&bch->bc_lock){+.+.}-{3:3}:
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
spin_lock include/linux/spinlock.h:351 [inline]
xfs_buf_rele_cached fs/xfs/xfs_buf.c:1093 [inline]
xfs_buf_rele+0x2bf/0x1660 fs/xfs/xfs_buf.c:1147
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317
worker_thread+0x870/0xd30 kernel/workqueue.c:3398
kthread+0x7a9/0x920 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #0 (&bp->b_lock){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3163 [inline]
check_prevs_add kernel/locking/lockdep.c:3282 [inline]
validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906
__lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
spin_lock include/linux/spinlock.h:351 [inline]
xfs_buf_try_hold fs/xfs/xfs_buf.c:578 [inline]
xfs_buf_find_insert+0x1123/0x1610 fs/xfs/xfs_buf.c:663
xfs_buf_get_map+0x149a/0x1ac0 fs/xfs/xfs_buf.c:754
xfs_buf_read_map+0x110/0xa50 fs/xfs/xfs_buf.c:862
xfs_trans_read_buf_map+0x260/0xab0 fs/xfs/xfs_trans_buf.c:304
xfs_trans_read_buf fs/xfs/xfs_trans.h:212 [inline]
xfs_imap_to_bp+0x18d/0x380 fs/xfs/libxfs/xfs_inode_buf.c:139
xfs_iget_cache_miss fs/xfs/xfs_icache.c:664 [inline]
xfs_iget+0xbe9/0x2ec0 fs/xfs/xfs_icache.c:806
xfs_lookup+0x356/0x690 fs/xfs/xfs_inode.c:553
xfs_vn_lookup+0x192/0x290 fs/xfs/xfs_iops.c:326
__lookup_slow+0x296/0x400 fs/namei.c:1793
lookup_slow+0x53/0x70 fs/namei.c:1810
walk_component+0x2e1/0x410 fs/namei.c:2114
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x16f/0x450 fs/namei.c:2636
filename_lookup+0x2a3/0x670 fs/namei.c:2665
do_linkat+0x13f/0x6f0 fs/namei.c:4845
__do_sys_link fs/namei.c:4899 [inline]
__se_sys_link fs/namei.c:4897 [inline]
__x64_sys_link+0x82/0x90 fs/namei.c:4897
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&bch->bc_lock);
lock(&bp->b_lock);
lock(&bch->bc_lock);
lock(&bp->b_lock);

*** DEADLOCK ***

2 locks held by syz-executor278/5867:
#0: ffff8880787e67f0 (&inode->i_sb->s_type->i_mutex_dir_key){.+.+}-{4:4}, at: inode_lock_shared include/linux/fs.h:875 [inline]
#0: ffff8880787e67f0 (&inode->i_sb->s_type->i_mutex_dir_key){.+.+}-{4:4}, at: lookup_slow+0x45/0x70 fs/namei.c:1809
#1: ffff888026f07980 (&bch->bc_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
#1: ffff888026f07980 (&bch->bc_lock){+.+.}-{3:3}, at: xfs_buf_find_insert+0x3da/0x1610 fs/xfs/xfs_buf.c:655

stack backtrace:
CPU: 0 UID: 0 PID: 5867 Comm: syz-executor278 Not tainted 6.13.0-syzkaller-09793-g69b8923f5003 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2076
check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2208
check_prev_add kernel/locking/lockdep.c:3163 [inline]
check_prevs_add kernel/locking/lockdep.c:3282 [inline]
validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906
__lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
spin_lock include/linux/spinlock.h:351 [inline]
xfs_buf_try_hold fs/xfs/xfs_buf.c:578 [inline]
xfs_buf_find_insert+0x1123/0x1610 fs/xfs/xfs_buf.c:663
xfs_buf_get_map+0x149a/0x1ac0 fs/xfs/xfs_buf.c:754
xfs_buf_read_map+0x110/0xa50 fs/xfs/xfs_buf.c:862
xfs_trans_read_buf_map+0x260/0xab0 fs/xfs/xfs_trans_buf.c:304
xfs_trans_read_buf fs/xfs/xfs_trans.h:212 [inline]
xfs_imap_to_bp+0x18d/0x380 fs/xfs/libxfs/xfs_inode_buf.c:139
xfs_iget_cache_miss fs/xfs/xfs_icache.c:664 [inline]
xfs_iget+0xbe9/0x2ec0 fs/xfs/xfs_icache.c:806
xfs_lookup+0x356/0x690 fs/xfs/xfs_inode.c:553
xfs_vn_lookup+0x192/0x290 fs/xfs/xfs_iops.c:326
__lookup_slow+0x296/0x400 fs/namei.c:1793
lookup_slow+0x53/0x70 fs/namei.c:1810
walk_component+0x2e1/0x410 fs/namei.c:2114
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x16f/0x450 fs/namei.c:2636
filename_lookup+0x2a3/0x670 fs/namei.c:2665
do_linkat+0x13f/0x6f0 fs/namei.c:4845
__do_sys_link fs/namei.c:4899 [inline]
__se_sys_link fs/namei.c:4897 [inline]
__x64_sys_link+0x82/0x90 fs/namei.c:4897
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f681317ba59
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6813111218 EFLAGS: 00000246 ORIG_RAX: 0000000000000056
RAX: ffffffffffffffda RBX: 00007f681320d6b8 RCX: 00007f681317ba59
RDX: 00007f68131550c6 RSI: 0000000000000000 RDI: 0000000020000040
RBP: 00007f681320d6b0 R08: 00007ffc23404e87 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0031656c69662f2e
R13: 0030656c69662f2e R14: 0031656c69662f30 R15: 2f30656c69662f2e
</TASK>

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