[syzbot ci] Re: AG aware parallel writeback for XFS

[syzbot ci]

syzbot ci has tested the following series

[v3] AG aware parallel writeback for XFS
https://lore.kernel.org/all/20260116100818.75...@samsung.com
* [PATCH v3 1/6] iomap: add write ops hook to attach metadata to folios
* [PATCH v3 2/6] xfs: add helpers to pack AG prediction info for per-folio tracking
* [PATCH v3 3/6] xfs: add per-inode AG prediction map and dirty-AG bitmap
* [PATCH v3 4/6] xfs: tag folios with AG number during buffered write via iomap attach hook
* [PATCH v3 5/6] xfs: add per-AG writeback workqueue infrastructure
* [PATCH v3 6/6] xfs: offload writeback by AG using per-inode dirty bitmap and per-AG workers

and found the following issue:
WARNING in xfs_init_ag_writeback

Full report is available here:
https://ci.syzbot.org/series/0e34236b-3594-400f-b9cd-6f59b196014f

***

WARNING in xfs_init_ag_writeback

tree: mm-new
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
base: eeb33083cc4749bdb61582eaeb5c200702607703
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/f21aae46-4d21-4410-9132-190ad8ae3994/config
C repro: https://ci.syzbot.org/findings/24ec6312-5e15-4750-aa2a-08d381daca26/c_repro
syz repro: https://ci.syzbot.org/findings/24ec6312-5e15-4750-aa2a-08d381daca26/syz_repro

loop2: detected capacity change from 0 to 32768
------------[ cut here ]------------
kmem_cache of name 'xfs_ag_wb_task' already exists
WARNING: mm/slab_common.c:110 at kmem_cache_sanity_check mm/slab_common.c:109 [inline], CPU#1: syz.2.19/6098
WARNING: mm/slab_common.c:110 at __kmem_cache_create_args+0x99/0x310 mm/slab_common.c:310, CPU#1: syz.2.19/6098
Modules linked in:
CPU: 1 UID: 0 PID: 6098 Comm: syz.2.19 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:kmem_cache_sanity_check mm/slab_common.c:109 [inline]
RIP: 0010:__kmem_cache_create_args+0x9c/0x310 mm/slab_common.c:310
Code: 43 8e 4d 8b 24 24 49 81 fc b8 78 43 8e 74 20 49 8b 7c 24 f8 48 89 de e8 f2 c0 67 09 85 c0 75 e2 48 8d 3d f7 ca bc 0d 48 89 de <67> 48 0f b9 3a 48 89 df be 20 00 00 00 e8 92 c2 67 09 48 85 c0 0f
RSP: 0018:ffffc90003817a08 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffffff8bc734a0 RCX: 0000000000000007
RDX: 000000008bc73406 RSI: ffffffff8bc734a0 RDI: ffffffff8fc6ee40
RBP: 0000000000080000 R08: ffffffff8fc26e77 R09: 1ffffffff1f84dce
R10: dffffc0000000000 R11: fffffbfff1f84dcf R12: ffff88810b7a7300
R13: ffff888115440000 R14: ffffc90003817aa0 R15: 0000000000000190
FS: 0000555567cf7500(0000) GS:ffff8882a9a05000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f049ffff000 CR3: 00000001b9726000 CR4: 00000000000006f0
Call Trace:
<TASK>
__kmem_cache_create include/linux/slab.h:384 [inline]
xfs_init_ag_writeback+0x41b/0x570 fs/xfs/xfs_aops.c:890
xfs_fs_fill_super+0x7e3/0x1640 fs/xfs/xfs_super.c:1759
get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1691
vfs_get_tree+0x92/0x2a0 fs/super.c:1751
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount+0x329/0xa50 fs/namespace.c:3712
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4201
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f32c139bf4a
Code: 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd30494b68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffd30494bf0 RCX: 00007f32c139bf4a
RDX: 0000200000009740 RSI: 0000200000009780 RDI: 00007ffd30494bb0
RBP: 0000200000009740 R08: 00007ffd30494bf0 R09: 0000000000004010
R10: 0000000000004010 R11: 0000000000000246 R12: 0000200000009780
R13: 00007ffd30494bb0 R14: 0000000000009768 R15: 0000200000000300
</TASK>
----------------
Code disassembly (best guess):
0: 43 8e 4d 8b rex.XB mov -0x75(%r13),%cs
4: 24 24 and $0x24,%al
6: 49 81 fc b8 78 43 8e cmp $0xffffffff8e4378b8,%r12
d: 74 20 je 0x2f
f: 49 8b 7c 24 f8 mov -0x8(%r12),%rdi
14: 48 89 de mov %rbx,%rsi
17: e8 f2 c0 67 09 call 0x967c10e
1c: 85 c0 test %eax,%eax
1e: 75 e2 jne 0x2
20: 48 8d 3d f7 ca bc 0d lea 0xdbccaf7(%rip),%rdi # 0xdbccb1e
27: 48 89 de mov %rbx,%rsi
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: 48 89 df mov %rbx,%rdi
32: be 20 00 00 00 mov $0x20,%esi
37: e8 92 c2 67 09 call 0x967c2ce
3c: 48 85 c0 test %rax,%rax
3f: 0f .byte 0xf


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syz...@syzkaller.appspotmail.com

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