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

[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 <ardb@xxxxxxxxxx>
Date:   Wed Apr 12 09:50:20 2023 +0100

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


On Sat, May 6, 2023 at 12:04 AM syzbot
<syzbot+d4b00edc2d0c910d4bf4@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> 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+d4b00edc2d0c910d4bf4@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> 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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>
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