[syzbot] [mm?] WARNING in __bch2_writepage

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cbf658dd0941 Merge tag 'net-6.17-rc7' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1702c712580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bf99f2510ef92ba5
dashboard link: https://syzkaller.appspot.com/bug?extid=682a660800143ff55ffe
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-cbf658dd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a976546d6ce4/vmlinux-cbf658dd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/13baef55a10d/bzImage-cbf658dd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+682a66...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 32768
bcachefs (loop0): starting version 1.7: mi_btree_bitmap opts=errors=continue,metadata_checksum=none,data_checksum=none,compression=lz4,nocow
allowing incompatible features above 0.0: (unknown version)
features: lz4,new_siphash,inline_data,new_extent_overwrite,btree_ptr_v2,new_varint,journal_no_flush,alloc_v2,extents_across_btree_nodes
bcachefs (loop0): Using encoding defined by superblock: utf8-12.1.0
bcachefs (loop0): initializing new filesystem
bcachefs (loop0): going read-write
bcachefs (loop0): marking superblocks
bcachefs (loop0): initializing freespace
bcachefs (loop0): done initializing freespace
bcachefs (loop0): reading snapshots table
bcachefs (loop0): reading snapshots done
bcachefs (loop0): loop0: Superblock write was silently dropped! (seq 0 expected 42)
bcachefs (loop0): done starting filesystem
------------[ cut here ]------------
WARNING: CPU: 0 PID: 5357 at mm/page_alloc.c:4619 __alloc_pages_slowpath+0xcb3/0xce0 mm/page_alloc.c:4619
Modules linked in:
CPU: 0 UID: 0 PID: 5357 Comm: syz.0.0 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
RIP: 0010:__alloc_pages_slowpath+0xcb3/0xce0 mm/page_alloc.c:4619
Code: d8 48 c1 e8 03 0f b6 04 08 84 c0 75 2e f6 43 01 08 48 8b 14 24 0f 84 a2 f3 ff ff 90 0f 0b 90 e9 99 f3 ff ff e8 be 7b 64 09 90 <0f> 0b 90 f7 c5 00 04 00 00 75 bc 90 0f 0b 90 eb b6 89 d9 80 e1 07
RSP: 0018:ffffc9000d396e50 EFLAGS: 00010246
RAX: dff18e3eab6b8600 RBX: 0000000000000002 RCX: dffffc0000000000
RDX: ffffc9000d396f60 RSI: 0000000000000002 RDI: 0000000000048c40
RBP: 0000000000048c40 R08: ffff88801b6f303f R09: 1ffff110036de607
R10: dffffc0000000000 R11: ffffed10036de608 R12: ffffc9000d396f60
R13: 1ffff92001a72de8 R14: 0000000000048c40 R15: dffffc0000000000
FS: 00007fa3c72006c0(0000) GS:ffff88808d009000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000200000 CR3: 000000003e644000 CR4: 0000000000352ef0
Call Trace:
<TASK>
__alloc_frozen_pages_noprof+0x319/0x370 mm/page_alloc.c:5161
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2492 [inline]
allocate_slab+0xd9/0x370 mm/slub.c:2668
new_slab mm/slub.c:2714 [inline]
___slab_alloc+0xbeb/0x1420 mm/slub.c:3901
__slab_alloc mm/slub.c:3992 [inline]
__slab_alloc_node mm/slub.c:4067 [inline]
slab_alloc_node mm/slub.c:4228 [inline]
__do_kmalloc_node mm/slub.c:4375 [inline]
__kmalloc_noprof+0x305/0x4f0 mm/slub.c:4388
kmalloc_noprof include/linux/slab.h:909 [inline]
kmalloc_array_noprof include/linux/slab.h:948 [inline]
__bch2_writepage+0x653/0x2790 fs/bcachefs/fs-io-buffered.c:563
write_cache_pages+0x61/0x100 mm/page-writeback.c:2612
bch2_writepages+0xf9/0x2d0 fs/bcachefs/fs-io-buffered.c:666
do_writepages+0x32e/0x550 mm/page-writeback.c:2634
filemap_fdatawrite_wbc mm/filemap.c:386 [inline]
__filemap_fdatawrite_range mm/filemap.c:419 [inline]
file_write_and_wait_range+0x23e/0x340 mm/filemap.c:794
bch2_fsync+0x127/0x330 fs/bcachefs/fs-io.c:245
generic_write_sync include/linux/fs.h:3043 [inline]
bch2_write_iter+0x2822/0x2b90 fs/bcachefs/fs-io-buffered.c:1089
aio_write+0x535/0x7a0 fs/aio.c:1634
__io_submit_one fs/aio.c:-1 [inline]
io_submit_one+0x78b/0x1310 fs/aio.c:2053
__do_sys_io_submit fs/aio.c:2112 [inline]
__se_sys_io_submit+0x185/0x2f0 fs/aio.c:2082
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa3c638eba9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa3c7200038 EFLAGS: 00000246 ORIG_RAX: 00000000000000d1
RAX: ffffffffffffffda RBX: 00007fa3c65d5fa0 RCX: 00007fa3c638eba9
RDX: 0000200000000540 RSI: 0000000000000018 RDI: 00007fa3c71be000
RBP: 00007fa3c6411e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa3c65d6038 R14: 00007fa3c65d5fa0 R15: 00007ffd247f0388
</TASK>


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