[syzbot] [xfs?] possible deadlock in xfs_trans_alloc

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4a26e7032d7d Merge tag 'core-bugs-2025-12-01' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12529512580000
kernel config: https://syzkaller.appspot.com/x/.config?x=553f3db6410d5a82
dashboard link: https://syzkaller.appspot.com/bug?extid=f4c587833618ec4a76f9
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-4a26e703.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bf3025099b65/vmlinux-4a26e703.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9e022e7e7365/bzImage-4a26e703.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f4c587...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kswapd0/79 is trying to acquire lock:
ffff88803fad6610 (sb_internal#2){.+.+}-{0:0}, at: xfs_trans_alloc+0xd7/0x960 fs/xfs/xfs_trans.c:256

but task is already holding lock:
ffffffff8e04ee20 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:7015 [inline]
ffffffff8e04ee20 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0x8ce/0x2780 mm/vmscan.c:7389

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (fs_reclaim){+.+.}-{0:0}:
__fs_reclaim_acquire mm/page_alloc.c:4264 [inline]
fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4278
might_alloc include/linux/sched/mm.h:318 [inline]
slab_pre_alloc_hook mm/slub.c:4929 [inline]
slab_alloc_node mm/slub.c:5264 [inline]
__kmalloc_cache_noprof+0x40/0x6e0 mm/slub.c:5766
kmalloc_noprof include/linux/slab.h:957 [inline]
iomap_fill_dirty_folios+0xf4/0x260 fs/iomap/buffered-io.c:1557
xfs_buffered_write_iomap_begin+0xa23/0x1a70 fs/xfs/xfs_iomap.c:1857
iomap_iter+0x5ef/0xeb0 fs/iomap/iter.c:110
iomap_zero_range+0x1cc/0xa30 fs/iomap/buffered-io.c:1590
xfs_zero_range+0x9a/0x100 fs/xfs/xfs_iomap.c:2289
xfs_setattr_size+0x48b/0xed0 fs/xfs/xfs_iops.c:993
__xfs_file_fallocate+0x10ca/0x15f0 include/linux/fs.h:-1
xfs_file_fallocate+0x27b/0x340 fs/xfs/xfs_file.c:1462
vfs_fallocate+0x669/0x7e0 fs/open.c:339
ksys_fallocate fs/open.c:363 [inline]
__do_sys_fallocate fs/open.c:368 [inline]
__se_sys_fallocate fs/open.c:366 [inline]
__x64_sys_fallocate+0xc0/0x110 fs/open.c:366
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&xfs_nondir_ilock_class){++++}-{4:4}:
down_write_nested+0x9d/0x200 kernel/locking/rwsem.c:1706
xfs_trans_alloc_ichange+0x1e6/0x6e0 fs/xfs/xfs_trans.c:1252
xfs_setattr_nonsize+0x402/0xcb0 fs/xfs/xfs_iops.c:837
xfs_setattr_size+0x294/0xed0 fs/xfs/xfs_iops.c:944
xfs_vn_setattr+0x258/0x300 fs/xfs/xfs_iops.c:1171
notify_change+0xc1a/0xf40 fs/attr.c:546
do_truncate+0x1a4/0x220 fs/open.c:68
handle_truncate fs/namei.c:4235 [inline]
do_open fs/namei.c:4632 [inline]
path_openat+0x359d/0x3dd0 fs/namei.c:4787
do_filp_open+0x1fa/0x410 fs/namei.c:4814
do_sys_openat2+0x121/0x200 fs/open.c:1430
do_sys_open fs/open.c:1436 [inline]
__do_sys_open fs/open.c:1444 [inline]
__se_sys_open fs/open.c:1440 [inline]
__x64_sys_open+0x11e/0x150 fs/open.c:1440
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#2){.+.+}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
__sb_start_write include/linux/fs/super.h:19 [inline]
sb_start_intwrite include/linux/fs/super.h:177 [inline]
__xfs_trans_alloc+0xad/0x420 fs/xfs/xfs_trans.c:224
xfs_trans_alloc+0xd7/0x960 fs/xfs/xfs_trans.c:256
xfs_fs_dirty_inode+0x12f/0x1e0 fs/xfs/xfs_super.c:735
__mark_inode_dirty+0x390/0x1330 fs/fs-writeback.c:2587
mark_inode_dirty_sync include/linux/fs.h:2200 [inline]
iput+0x3e8/0x1030 fs/inode.c:1984
__dentry_kill+0x209/0x660 fs/dcache.c:670
shrink_kill+0xa9/0x2c0 fs/dcache.c:1115
shrink_dentry_list+0x2e0/0x5e0 fs/dcache.c:1142
prune_dcache_sb+0x10e/0x180 fs/dcache.c:1223
super_cache_scan+0x369/0x4b0 fs/super.c:222
do_shrink_slab+0x6df/0x10d0 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+0x13f5/0x2780 mm/vmscan.c:7389
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x52d/0xa60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
sb_internal#2 --> &xfs_nondir_ilock_class --> fs_reclaim

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(fs_reclaim);
lock(&xfs_nondir_ilock_class);
lock(fs_reclaim);
rlock(sb_internal#2);

*** DEADLOCK ***

2 locks held by kswapd0/79:
#0: ffffffff8e04ee20 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:7015 [inline]
#0: ffffffff8e04ee20 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0x8ce/0x2780 mm/vmscan.c:7389
#1: ffff88803fad60e0 (&type->s_umount_key#50){.+.+}-{4:4}, at: super_trylock_shared fs/super.c:563 [inline]
#1: ffff88803fad60e0 (&type->s_umount_key#50){.+.+}-{4:4}, at: super_cache_scan+0x91/0x4b0 fs/super.c:197

stack backtrace:
CPU: 0 UID: 0 PID: 79 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+0x2e2/0x300 kernel/locking/lockdep.c:2043
check_noncircular+0x12e/0x150 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 kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
__sb_start_write include/linux/fs/super.h:19 [inline]
sb_start_intwrite include/linux/fs/super.h:177 [inline]
__xfs_trans_alloc+0xad/0x420 fs/xfs/xfs_trans.c:224
xfs_trans_alloc+0xd7/0x960 fs/xfs/xfs_trans.c:256
xfs_fs_dirty_inode+0x12f/0x1e0 fs/xfs/xfs_super.c:735
__mark_inode_dirty+0x390/0x1330 fs/fs-writeback.c:2587
mark_inode_dirty_sync include/linux/fs.h:2200 [inline]
iput+0x3e8/0x1030 fs/inode.c:1984
__dentry_kill+0x209/0x660 fs/dcache.c:670
shrink_kill+0xa9/0x2c0 fs/dcache.c:1115
shrink_dentry_list+0x2e0/0x5e0 fs/dcache.c:1142
prune_dcache_sb+0x10e/0x180 fs/dcache.c:1223
super_cache_scan+0x369/0x4b0 fs/super.c:222
do_shrink_slab+0x6df/0x10d0 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+0x13f5/0x2780 mm/vmscan.c:7389
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x52d/0xa60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


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