[v6.1] BUG: unable to handle kernel paging request in fq_codel_enqueue

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3594f306da12 Linux 6.1.147
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=119c5834580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2be97b627a5d7554
dashboard link: https://syzkaller.appspot.com/bug?extid=339e7ece7243e5f5ff77
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0d2a884e198e/disk-3594f306.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/23d3643328c7/vmlinux-3594f306.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ef83d78711e3/Image-3594f306.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+339e7e...@syzkaller.appspotmail.com

Unable to handle kernel paging request at virtual address dfff800000000000
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
Mem abort info:
ESR = 0x0000000096000006
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x06: level 2 translation fault
Data abort info:
ISV = 0, ISS = 0x00000006
CM = 0, WnR = 0
[dfff800000000000] address between user and kernel address ranges
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 4297 Comm: udevd Not tainted 6.1.147-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : dequeue_head net/sched/sch_fq_codel.c:120 [inline]
pc : fq_codel_drop net/sched/sch_fq_codel.c:168 [inline]
pc : fq_codel_enqueue+0x79c/0xf38 net/sched/sch_fq_codel.c:230
lr : fq_codel_drop net/sched/sch_fq_codel.c:162 [inline]
lr : fq_codel_enqueue+0x728/0xf38 net/sched/sch_fq_codel.c:230
sp : ffff8000080074a0
x29: ffff8000080075a0 x28: 0000000000000000 x27: 0000000000000000
x26: 0000000000000000 x25: 0000000000000001 x24: ffff0000d9965c00
x23: 0000000000000000 x22: ffff0000dce652d0 x21: ffff800008007860
x20: dfff800000000000 x19: 0000000000000000 x18: 00000000ae1f9abe
x17: ffff8000181e7000 x16: ffff8000082d2374 x15: ffff800017cc7fc0
x14: ffff0000d3f44218 x13: 1ffff00002a160b1 x12: 0000000000ff0100
x11: ff0080000ff9d370 x10: 0000000000000000 x9 : 1fffe0001b32cb80
x8 : 0000000000000000 x7 : ffff8000083b9874 x6 : 0000000000000000
x5 : 0000000000000080 x4 : 0000000000000001 x3 : 0000000000000000
x2 : ffff0000dce65328 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
dequeue_head net/sched/sch_fq_codel.c:120 [inline]
fq_codel_drop net/sched/sch_fq_codel.c:168 [inline]
fq_codel_enqueue+0x79c/0xf38 net/sched/sch_fq_codel.c:230
qdisc_enqueue include/net/sch_generic.h:816 [inline]
sfb_enqueue+0x794/0x1294 net/sched/sch_sfb.c:405
dev_qdisc_enqueue+0x5c/0x38c net/core/dev.c:3863
__dev_xmit_skb net/core/dev.c:3952 [inline]
__dev_queue_xmit+0xad0/0x309c net/core/dev.c:4300
dev_queue_xmit include/linux/netdevice.h:3051 [inline]
tipc_l2_send_msg+0x29c/0x35c net/tipc/bearer.c:518
tipc_bearer_xmit_skb+0x244/0x384 net/tipc/bearer.c:577
tipc_disc_timeout+0x4c8/0x608 net/tipc/discover.c:338
call_timer_fn+0x1b8/0x964 kernel/time/timer.c:1504
expire_timers kernel/time/timer.c:1549 [inline]
__run_timers+0x460/0x6bc kernel/time/timer.c:1820
run_timer_softirq+0x7c/0x114 kernel/time/timer.c:1833
handle_softirqs+0x318/0xc6c kernel/softirq.c:596
__do_softirq+0x14/0x20 kernel/softirq.c:630
____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:80
call_on_irq_stack+0x24/0x30 arch/arm64/kernel/entry.S:849
do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:85
invoke_softirq kernel/softirq.c:477 [inline]
__irq_exit_rcu+0x23c/0x43c kernel/softirq.c:679
irq_exit_rcu+0x14/0x84 kernel/softirq.c:691
__el1_irq arch/arm64/kernel/entry-common.c:472 [inline]
el1_interrupt+0x38/0x54 arch/arm64/kernel/entry-common.c:486
el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:491
el1h_64_irq+0x64/0x68 arch/arm64/kernel/entry.S:581
arch_local_irq_restore arch/arm64/include/asm/irqflags.h:122 [inline]
seqcount_lockdep_reader_access include/linux/seqlock.h:104 [inline]
set_root+0x204/0x48c fs/namei.c:945
nd_jump_root+0x26c/0x3cc fs/namei.c:966
path_init+0x37c/0x1120 fs/namei.c:2389
path_openat+0x12c/0x2680 fs/namei.c:3778
do_filp_open+0x174/0x344 fs/namei.c:3810
do_sys_openat2+0x128/0x3d8 fs/open.c:1318
do_sys_open fs/open.c:1334 [inline]
__do_sys_openat fs/open.c:1350 [inline]
__se_sys_openat fs/open.c:1345 [inline]
__arm64_sys_openat+0x120/0x154 fs/open.c:1345
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
Code: aa1803e0 9624e4c0 f9400317 d343fee8 (38746908)
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
0: aa1803e0 mov x0, x24
4: 9624e4c0 bl 0xfffffffff8939304
8: f9400317 ldr x23, [x24]
c: d343fee8 lsr x8, x23, #3
* 10: 38746908 ldrb w8, [x8, x20] <-- trapping instruction


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.