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Message-ID: <aS6X08yD5yK8d8EG@infradead.org>
Date: Mon, 1 Dec 2025 23:40:03 -0800
From: Christoph Hellwig <hch@...radead.org>
To: syzbot <syzbot+789028412a4af61a2b61@...kaller.appspotmail.com>
Cc: cem@...nel.org, linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
mmpgouride@...il.com, syzkaller-bugs@...glegroups.com,
Brian Foster <bfoster@...hat.com>
Subject: Re: [syzbot] [xfs?] possible deadlock in xfs_icwalk_ag (3)
This look like the batch zeroing code. I think we have a patch pending
to remove the allocation, but I lost track a bit where we are with that.
On Mon, Dec 01, 2025 at 06:06:22PM -0800, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 1d18101a644e Merge tag 'kernel-6.19-rc1.cred' of git://git..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=119238c2580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=a1db0fea040c2a9f
> dashboard link: https://syzkaller.appspot.com/bug?extid=789028412a4af61a2b61
> compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1407a512580000
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-1d18101a.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/98f78b52cccd/vmlinux-1d18101a.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7a8898061bfb/bzImage-1d18101a.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/9f625d767816/mount_0.gz
> fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=1406a192580000)
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+789028412a4af61a2b61@...kaller.appspotmail.com
>
> ======================================================
> WARNING: possible circular locking dependency detected
> syzkaller #0 Not tainted
> ------------------------------------------------------
> kswapd0/73 is trying to acquire lock:
> ffff88804146c118 (&xfs_nondir_ilock_class){++++}-{4:4}, at: xfs_reclaim_inode fs/xfs/xfs_icache.c:1040 [inline]
> ffff88804146c118 (&xfs_nondir_ilock_class){++++}-{4:4}, at: xfs_icwalk_process_inode fs/xfs/xfs_icache.c:1732 [inline]
> ffff88804146c118 (&xfs_nondir_ilock_class){++++}-{4:4}, at: xfs_icwalk_ag+0x12c5/0x1ab0 fs/xfs/xfs_icache.c:1814
>
> but task is already holding lock:
> ffffffff8e047ae0 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:7015 [inline]
> ffffffff8e047ae0 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0x951/0x2800 mm/vmscan.c:7389
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (fs_reclaim){+.+.}-{0:0}:
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
> __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+0x40/0x6f0 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+0x5f2/0xf10 fs/iomap/iter.c:110
> iomap_zero_range+0x1cc/0xa50 fs/iomap/buffered-io.c:1590
> xfs_zero_range+0x9a/0x100 fs/xfs/xfs_iomap.c:2289
> xfs_reflink_remap_prep+0x398/0x720 fs/xfs/xfs_reflink.c:1699
> xfs_file_remap_range+0x235/0x780 fs/xfs/xfs_file.c:1518
> vfs_copy_file_range+0xd81/0x1370 fs/read_write.c:1598
> __do_sys_copy_file_range fs/read_write.c:1681 [inline]
> __se_sys_copy_file_range+0x2fb/0x470 fs/read_write.c:1648
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> -> #0 (&xfs_nondir_ilock_class){++++}-{4:4}:
> 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_write_nested+0x9d/0x200 kernel/locking/rwsem.c:1706
> xfs_reclaim_inode fs/xfs/xfs_icache.c:1040 [inline]
> xfs_icwalk_process_inode fs/xfs/xfs_icache.c:1732 [inline]
> xfs_icwalk_ag+0x12c5/0x1ab0 fs/xfs/xfs_icache.c:1814
> xfs_icwalk fs/xfs/xfs_icache.c:1862 [inline]
> xfs_reclaim_inodes_nr+0x1e3/0x260 fs/xfs/xfs_icache.c:1106
> super_cache_scan+0x41b/0x4b0 fs/super.c:228
> do_shrink_slab+0x6ef/0x1110 mm/shrinker.c:437
> shrink_slab+0xd74/0x10d0 mm/shrinker.c:664
> 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+0x711/0x8a0 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
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(fs_reclaim);
> lock(&xfs_nondir_ilock_class);
> lock(fs_reclaim);
> lock(&xfs_nondir_ilock_class);
>
> *** DEADLOCK ***
>
> 2 locks held by kswapd0/73:
> #0: ffffffff8e047ae0 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:7015 [inline]
> #0: ffffffff8e047ae0 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0x951/0x2800 mm/vmscan.c:7389
> #1: ffff8880119bc0e0 (&type->s_umount_key#54){++++}-{4:4}, at: super_trylock_shared fs/super.c:563 [inline]
> #1: ffff8880119bc0e0 (&type->s_umount_key#54){++++}-{4:4}, at: super_cache_scan+0x91/0x4b0 fs/super.c:197
>
> 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_write_nested+0x9d/0x200 kernel/locking/rwsem.c:1706
> xfs_reclaim_inode fs/xfs/xfs_icache.c:1040 [inline]
> xfs_icwalk_process_inode fs/xfs/xfs_icache.c:1732 [inline]
> xfs_icwalk_ag+0x12c5/0x1ab0 fs/xfs/xfs_icache.c:1814
> xfs_icwalk fs/xfs/xfs_icache.c:1862 [inline]
> xfs_reclaim_inodes_nr+0x1e3/0x260 fs/xfs/xfs_icache.c:1106
> super_cache_scan+0x41b/0x4b0 fs/super.c:228
> do_shrink_slab+0x6ef/0x1110 mm/shrinker.c:437
> shrink_slab+0xd74/0x10d0 mm/shrinker.c:664
> 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+0x711/0x8a0 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>
>
>
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>
---end quoted text---
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