BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof (2)

Status: fixed on 2025/09/04 16:56
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+56edda805363e0a093b8@syzkaller.appspotmail.com
Fix commit: 56be92c63f02 bcachefs: Fix pool->alloc NULL pointer dereference
First crash: 460d, last: 403d
Cause bisection: introduced by (bisect log) :
commit d4d71b58e5139afc5f9bda0139b99404eb216d8a
Author: Kent Overstreet <kent.overstreet@linux.dev>
Date: Sat Apr 5 21:36:04 2025 +0000

  bcachefs: RO mounts now use less memory

Crash: BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof (log)
Repro: C syz .config
  
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [bcachefs?] BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof (2) 1 (3) 2025/07/18 17:48
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof block 10 3 760d 789d 0/29 auto-obsoleted due to no activity on 2024/09/23 15:37
upstream BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof (3) fs 10 1 319d 314d 0/29 auto-obsoleted due to no activity on 2025/12/18 14:09
▶ ▼ Last patch testing requests (4)
Created Duration User Patch Repo Result
2025/07/02 01:52 2h05m retest repro upstream OK log
2025/07/02 01:52 1h53m retest repro upstream OK log
2025/07/02 01:52 1h29m retest repro upstream OK log
2025/07/01 12:11 21m retest repro upstream OK log

Sample crash report:
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 PTI
CPU: 0 UID: 0 PID: 5834 Comm: syz-executor375 Not tainted 6.16.0-rc1-syzkaller-00157-g02adc1490e6d #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc900041b6d98 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff888072e03ef0
RDX: 1ffff1100e5c07de RSI: 0000000000000000 RDI: 0000000000092800
RBP: ffffc900041b6ef0 R08: ffffc900041b6e67 R09: 0000000000000000
R10: ffffc900041b6e40 R11: 0000000000000000 R12: 1ffff92000836dc4
R13: ffff888072e03ef0 R14: 0000000000092c40 R15: 0000000000092800
FS:  0000000000000000(0000) GS:ffff888125c84000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000339f4000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 mempool_alloc_noprof+0x1a4/0x510 mm/mempool.c:402
 bch2_btree_update_start+0x572/0x1dc0 fs/bcachefs/btree_update_interior.c:1219
 bch2_btree_node_rewrite+0x17e/0x1120 fs/bcachefs/btree_update_interior.c:2245
 bch2_move_btree+0x6f0/0xc60 fs/bcachefs/move.c:1145
 bch2_scan_old_btree_nodes+0x95/0x240 fs/bcachefs/move.c:1266
 bch2_data_job+0x646/0x910 fs/bcachefs/move.c:1404
 bch2_data_thread+0x8f/0x1d0 fs/bcachefs/chardev.c:315
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 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:ffffc900041b6d98 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff888072e03ef0
RDX: 1ffff1100e5c07de RSI: 0000000000000000 RDI: 0000000000092800
RBP: ffffc900041b6ef0 R08: ffffc900041b6e67 R09: 0000000000000000
R10: ffffc900041b6e40 R11: 0000000000000000 R12: 1ffff92000836dc4
R13: ffff888072e03ef0 R14: 0000000000092c40 R15: 0000000000092800
FS:  0000000000000000(0000) GS:ffff888125c84000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000339f4000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Crashes (8):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/14 02:53 upstream 02adc1490e6d 0e8da31f .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-upstream-fs BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof
2025/06/14 00:59 upstream 02adc1490e6d 0e8da31f .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-upstream-fs BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof
2025/06/01 09:06 upstream 4cb6c8af8591 3d2f584d .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-upstream-fs BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof
2025/06/17 11:48 upstream 9afe652958c3 cfebc887 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof
2025/06/04 12:32 upstream 5abc7438f1e9 e565f08d .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof
2025/06/01 06:05 upstream 4cb6c8af8591 3d2f584d .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] [mounted in repro #1] [mounted in repro #2 (corrupt fs)] ci-snapshot-upstream-root BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof
2025/06/01 05:18 upstream 4cb6c8af8591 3d2f584d .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof
2025/04/21 05:14 upstream 6fea5fabd332 2a20f901 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root BUG: unable to handle kernel NULL pointer dereference in mempool_alloc_noprof
* Struck through repros no longer work on HEAD.