[syzbot] upstream boot error: BUG: unable to handle kernel NULL pointer dereference in load_balance

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1a5304fecee5 Merge tag 'parisc-for-6.4-1' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=125e1e5c280000
kernel config: https://syzkaller.appspot.com/x/.config?x=124f13edd5df0b0d
dashboard link: https://syzkaller.appspot.com/bug?extid=d4b00edc2d0c910d4bf4
compiler: arm-linux-gnueabi-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d4b00e...@syzkaller.appspotmail.com

8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 00000018 when read
[00000018] *pgd=80000080004003, *pmd=00000000
Internal error: Oops: 207 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.3.0-syzkaller #0
Hardware name: ARM-Versatile Express
PC is at find_next_and_bit include/linux/find.h:93 [inline]
PC is at should_we_balance kernel/sched/fair.c:10717 [inline]
PC is at load_balance+0x130/0xcdc kernel/sched/fair.c:10760
LR is at load_balance+0x78/0xcdc kernel/sched/fair.c:10743
pc : [<8028b604>] lr : [<8028b54c>] psr: 80000113
sp : df805df8 ip : df805e84 fp : df805ebc
r10: 8309a800 r9 : df805e84 r8 : 00000001
r7 : 8309a800 r6 : ddddb400 r5 : 830b4640 r4 : 00000001
r3 : 00000000 r2 : ddddb400 r1 : 00000000 r0 : df805e48
Flags: Nzcv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
Control: 30c5387d Table: 847ac040 DAC: 00000000
Register r0 information:
8<--- cut here ---
Unable to handle kernel paging request at virtual address df96bff8 when read
[df96bff8] *pgd=80000080007003, *pmd=83093003, *pte=8261d0a800000000
Internal error: Oops: 207 [#2] PREEMPT SMP ARM
Modules linked in:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.3.0-syzkaller #0
Hardware name: ARM-Versatile Express
PC is at __find_vmap_area mm/vmalloc.c:841 [inline]
PC is at find_vmap_area mm/vmalloc.c:1862 [inline]
PC is at find_vm_area mm/vmalloc.c:2623 [inline]
PC is at vmalloc_dump_obj+0x38/0xb4 mm/vmalloc.c:4221
LR is at __raw_spin_lock include/linux/spinlock_api_smp.h:132 [inline]
LR is at _raw_spin_lock+0x18/0x58 kernel/locking/spinlock.c:154
pc : [<8047a200>] lr : [<818015f4>] psr: a0000193
sp : df805c88 ip : df805c70 fp : df805c9c
r10: 831f4680 r9 : 8261c9a4 r8 : 8285041c
r7 : 60000113 r6 : 00000001 r5 : df806000 r4 : df96c000
r3 : 00000000 r2 : 00002268 r1 : 00000000 r0 : 00000001
Flags: NzCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment none
Control: 30c5387d Table: 847ac040 DAC: 00000000


---
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[Aleksandr Nogikh]

For the context: we've been seeing tons of different boot time errors
on the syzbot arm32 qemu instance.
Manual bisection points to this commit:

commit c76c6c4ecbec0deb56a4f9e932b26866024a508f
Author: Ard Biesheuvel <ar...@kernel.org>
Date: Wed Apr 12 09:50:20 2023 +0100

ARM: 9294/2: vfp: Fix broken softirq handling with instrumentation enabled

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[Aleksandr Nogikh]

On Sat, May 6, 2023 at 12:07 AM Aleksandr Nogikh <nog...@google.com> wrote:
>
> For the context: we've been seeing tons of different boot time errors
> on the syzbot arm32 qemu instance.

If that might help, here are some of those reports:
https://syzkaller.appspot.com/upstream?only_manager=ci-qemu2-arm32

[Ard Biesheuvel]

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git
f4fd69d8877146677709f66778c40bc3c7bcb40f

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+d4b00e...@syzkaller.appspotmail.com

Tested on:

commit: f4fd69d8 ARM: vfp: avoid unbalanced stack on 'success'..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git
kernel config: https://syzkaller.appspot.com/x/.config?x=c8dd4e2cced46f7e

dashboard link: https://syzkaller.appspot.com/bug?extid=d4b00edc2d0c910d4bf4
compiler: arm-linux-gnueabi-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.