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

[Aleksandr Nogikh]

On Sat, May 6, 2023 at 12:07 AM Aleksandr Nogikh <nogikh@xxxxxxxxxx> 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

> 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
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> >
> > If the bug is already fixed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> >
> > If you want to change bug's subsystems, reply with:
> > #syz set subsystems: new-subsystem
> > (See the list of subsystem names on the web dashboard)
> >
> > If the bug is a duplicate of another bug, reply with:
> > #syz dup: exact-subject-of-another-report
> >
> > If you want to undo deduplication, reply with:
> > #syz undup
> >
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