Re: [syzbot] [riscv?] kernel panic: Kernel stack overflow (3)

On 24/12/2024 14:29, syzbot wrote:

Hello,

syzbot found the following issue on:

HEAD commit:    21f1b85c8912 riscv: mm: Do not call pmd dtor on vmemmap pa..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
console output: https://syzkaller.appspot.com/x/log.txt?x=14d32adf980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=90afd41d36b4291d
dashboard link: https://syzkaller.appspot.com/bug?extid=f694b8c2ba2919587a3d
compiler:       riscv64-linux-gnu-gcc (Debian 12.2.0-13) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: riscv64

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/a741b348759c/non_bootable_disk-21f1b85c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/69f16f8d759e/vmlinux-21f1b85c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1e170e1b7a02/Image-21f1b85c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f694b8c2ba2919587a3d@syzkaller.appspotmail.com

  s11: ff6000001cefcec0 t3 : ff6000001cefd9e0 t4 : 1fec0000039dfb3b
  t5 : 1fec0000039dfba9 t6 : 0000000000000015
status: 0000000200000100 badaddr: ff20000005acff40 cause: 000000000000000f
Kernel panic - not syncing: Kernel stack overflow
CPU: 0 UID: 0 PID: 11449 Comm: syz.2.1759 Not tainted 6.13.0-rc2-syzkaller-g21f1b85c8912 #0
Hardware name: riscv-virtio,qemu (DT)
Call Trace:
[<ffffffff80071bae>] dump_backtrace+0x2e/0x3c arch/riscv/kernel/stacktrace.c:130
[<ffffffff8000325c>] show_stack+0x30/0x3c arch/riscv/kernel/stacktrace.c:136
[<ffffffff8005e1d6>] __dump_stack lib/dump_stack.c:94 [inline]
[<ffffffff8005e1d6>] dump_stack_lvl+0x110/0x1a6 lib/dump_stack.c:120
[<ffffffff8005e288>] dump_stack+0x1c/0x24 lib/dump_stack.c:129
[<ffffffff80003e62>] panic+0x38c/0x86e kernel/panic.c:354
[<ffffffff80071372>] handle_bad_stack+0xd4/0xfc arch/riscv/kernel/traps.c:427
[<ffffffff802b37e2>] mark_usage kernel/locking/lockdep.c:4658 [inline]
[<ffffffff802b37e2>] __lock_acquire+0xaa6/0x8594 kernel/locking/lockdep.c:5180
SMP: stopping secondary CPUs
Rebooting in 86400 seconds..


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We have the same stack size as x86 and arm64, which is 32KB. Given the 
fault address (ff20000005acff40), we indeed overflow the kernel stack:

[ 5560.063329][T11449] Task stack:     [0xff20000005ad0000..0xff20000005ad8000]

I noticed the following warning right before we lack space on the stack 
(which in the comments indicate a "recursion"):

[ 5560.055175][T11449] Dead loop on virtual device ipvlan1, fix it urgently!

Can the overflow be explained by this? Or should we again increase stack space? Or could this be a riscv specific issue?

I have no idea, so +cc netdev in case they can explain this.

Thanks for your help,

Alex