linux-kernel - [syzbot] [bcachefs?] BUG: unable to handle kernel NULL pointer dereference in mempool_alloc

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Message-ID: <68c67477.050a0220.2ff435.037f.GAE@google.com>
Date: Sun, 14 Sep 2025 00:53:27 -0700
From: syzbot <syzbot+4ebc8d586b68728bcad6@...kaller.appspotmail.com>
To: kent.overstreet@...ux.dev, linux-bcachefs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [bcachefs?] BUG: unable to handle kernel NULL pointer
 dereference in mempool_alloc_noprof (3)

Hello,

syzbot found the following issue on:

HEAD commit:    f777d1112ee5 Merge tag 'vfs-6.17-rc6.fixes' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1547ad62580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c7f605fd273c8220
dashboard link: https://syzkaller.appspot.com/bug?extid=4ebc8d586b68728bcad6
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-f777d111.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ff082b9d029e/vmlinux-f777d111.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e2c8489f25c3/bzImage-f777d111.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4ebc8d586b68728bcad6@...kaller.appspotmail.com

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: 5383 Comm: bch-rebalance/l 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: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc9000d49ec18 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff8880532c75a0
RDX: 1ffff1100a658eb4 RSI: 0000000000000000 RDI: 0000000000092800
RBP: ffffc9000d49ed70 R08: ffffc9000d49ece7 R09: 0000000000000000
R10: ffffc9000d49ecc0 R11: 0000000000000000 R12: 1ffff92001a93d94
R13: ffff8880532c75a0 R14: 0000000000092c40 R15: 0000000000092800
FS:  0000000000000000(0000) GS:ffff88808d20c000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000400eb000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 mempool_alloc_noprof+0x1a4/0x510 mm/mempool.c:406
 __bio_compress fs/bcachefs/compress.c:461 [inline]
 bch2_bio_compress+0x42f/0x14c0 fs/bcachefs/compress.c:555
 bch2_write_extent fs/bcachefs/io_write.c:1060 [inline]
 __bch2_write+0xfb5/0x3900 fs/bcachefs/io_write.c:1554
 move_write fs/bcachefs/move.c:217 [inline]
 bch2_moving_ctxt_do_pending_writes+0x5a7/0xe60 fs/bcachefs/move.c:248
 bch2_move_ratelimit+0x8e8/0x1330 fs/bcachefs/move.c:585
 do_rebalance fs/bcachefs/rebalance.c:557 [inline]
 bch2_rebalance_thread+0x17b0/0x1f80 fs/bcachefs/rebalance.c:626
 kthread+0x70e/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 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:ffffc9000d49ec18 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff8880532c75a0
RDX: 1ffff1100a658eb4 RSI: 0000000000000000 RDI: 0000000000092800
RBP: ffffc9000d49ed70 R08: ffffc9000d49ece7 R09: 0000000000000000
R10: ffffc9000d49ecc0 R11: 0000000000000000 R12: 1ffff92001a93d94
R13: ffff8880532c75a0 R14: 0000000000092c40 R15: 0000000000092800
FS:  0000000000000000(0000) GS:ffff88808d20c000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000400eb000 CR4: 0000000000352ef0


---
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