[moderation] [bcachefs?] BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof (2)

Hello,

syzbot found the following issue on:

HEAD commit: 6fea5fabd332 Merge tag 'mm-hotfixes-stable-2025-04-19-21-2..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17e6bfe4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=68d9f79fc685cd4
dashboard link: https://syzkaller.appspot.com/bug?extid=4a6d18640e49b9bd0bb3
compiler: Debian clang version 15.0.6, Debian LLD 15.0.6
CC: [[email protected] [email protected] [email protected]]

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-6fea5fab.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/196af7f3aabc/vmlinux-6fea5fab.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c8feb6df0b6a/bzImage-6fea5fab.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

bcachefs (loop0): compression opt none set but not marked in superblock, fixing
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 0 P4D 0
Oops: Oops: 0010 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5341 Comm: bch-rebalance/l Not tainted 6.15.0-rc2-syzkaller-00488-g6fea5fabd332 #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: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc9000d70ebd8 EFLAGS: 00010246
RAX: 1ffff1100a6c8e84 RBX: ffff888053647420 RCX: ffff888053647420
RDX: ffff8880007cc880 RSI: 0000000000000000 RDI: 0000000000092800
RBP: ffffc9000d70ed30 R08: ffffffff81fe7502 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000092800 R14: dffffc0000000000 R15: 0000000000092c40
FS: 0000000000000000(0000) GS:ffff88808c59a000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000044068000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
mempool_alloc_noprof+0x199/0x5a0 mm/mempool.c:402
__bio_compress fs/bcachefs/compress.c:461 [inline]
bch2_bio_compress+0x3ca/0x15c0 fs/bcachefs/compress.c:555
bch2_write_extent fs/bcachefs/io_write.c:1020 [inline]
__bch2_write+0x117c/0x46c0 fs/bcachefs/io_write.c:1515
bch2_write+0x834/0x15d0 fs/bcachefs/io_write.c:1681
move_write fs/bcachefs/move.c:160 [inline]
bch2_moving_ctxt_do_pending_writes+0x589/0xa70 fs/bcachefs/move.c:191
bch2_moving_ctxt_flush_all+0x269/0x3a0 fs/bcachefs/move.c:206
do_rebalance fs/bcachefs/rebalance.c:566 [inline]
bch2_rebalance_thread+0x1a42/0x1fa0 fs/bcachefs/rebalance.c:588
kthread+0x7b7/0x940 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
CR2: 0000000000000000
---[ end trace 0000000000000000 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc9000d70ebd8 EFLAGS: 00010246
RAX: 1ffff1100a6c8e84 RBX: ffff888053647420 RCX: ffff888053647420
RDX: ffff8880007cc880 RSI: 0000000000000000 RDI: 0000000000092800
RBP: ffffc9000d70ed30 R08: ffffffff81fe7502 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000092800 R14: dffffc0000000000 R15: 0000000000092c40
FS: 0000000000000000(0000) GS:ffff88808c59a000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000044068000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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