[syzbot] riscv/fixes boot error: can't ssh into the instance

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f6f7fbb89bf8 riscv: dts: sifive unmatched: Link the tmp451..
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=1095f85bb00000
kernel config: https://syzkaller.appspot.com/x/.config?x=522544a2e0ef2a7d
dashboard link: https://syzkaller.appspot.com/bug?extid=330a558d94b58f7601be
compiler: riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: riscv64

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+330a55...@syzkaller.appspotmail.com



---
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 syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[Aleksandr Nogikh]

Hello,

syzbot has already not been able to fuzz its RISC-V instance for 97
days now because the compiled kernel cannot boot. I bisected the issue
to the following commit:

commit 54c5639d8f507ebefa814f574cb6f763033a72a5
Author: Alexandre Ghiti <alexand...@canonical.com>
Date: Fri Oct 29 06:59:27 2021 +0200

riscv: Fix asan-stack clang build

Apparently, the problem appears on GCC-built RISC-V kernels with KASAN
enabled. In the previous message syzbot mentions

"riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU

Binutils for Debian) 2.35.2", but the issue also reproduces finely on
a newer GCC compiler: "riscv64-linux-gnu-gcc (Debian 11.2.0-10)
11.2.0, GNU ld (GNU Binutils for Debian) 2.37".
For convenience, I also duplicate the .config file from the bot's
message: https://syzkaller.appspot.com/x/.config?x=522544a2e0ef2a7d

Can someone with KASAN and RISC-V expertise please take a look?

--
Best Regards,
Aleksandr

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[Alexandre Ghiti]

Hi Aleksandr,

On Wed, Feb 2, 2022 at 12:08 PM Aleksandr Nogikh <nog...@google.com> wrote:
>
> Hello,
>
> syzbot has already not been able to fuzz its RISC-V instance for 97

That's a longtime, I'll take a look more regularly.

> days now because the compiled kernel cannot boot. I bisected the issue
> to the following commit:
>
> commit 54c5639d8f507ebefa814f574cb6f763033a72a5
> Author: Alexandre Ghiti <alexand...@canonical.com>
> Date: Fri Oct 29 06:59:27 2021 +0200
>
> riscv: Fix asan-stack clang build
>
> Apparently, the problem appears on GCC-built RISC-V kernels with KASAN
> enabled. In the previous message syzbot mentions
> "riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU
> Binutils for Debian) 2.35.2", but the issue also reproduces finely on
> a newer GCC compiler: "riscv64-linux-gnu-gcc (Debian 11.2.0-10)
> 11.2.0, GNU ld (GNU Binutils for Debian) 2.37".
> For convenience, I also duplicate the .config file from the bot's
> message: https://syzkaller.appspot.com/x/.config?x=522544a2e0ef2a7d
>
> Can someone with KASAN and RISC-V expertise please take a look?

I'll take a look at that today.

Thanks for reporting the issue,

Alex

[Dmitry Vyukov]

On Wed, 2 Feb 2022 at 14:18, Alexandre Ghiti
<alexand...@canonical.com> wrote:
>
> Hi Aleksandr,
>
> On Wed, Feb 2, 2022 at 12:08 PM Aleksandr Nogikh <nog...@google.com> wrote:
> >
> > Hello,
> >
> > syzbot has already not been able to fuzz its RISC-V instance for 97
>
> That's a longtime, I'll take a look more regularly.
>
> > days now because the compiled kernel cannot boot. I bisected the issue
> > to the following commit:
> >
> > commit 54c5639d8f507ebefa814f574cb6f763033a72a5
> > Author: Alexandre Ghiti <alexand...@canonical.com>
> > Date: Fri Oct 29 06:59:27 2021 +0200
> >
> > riscv: Fix asan-stack clang build
> >
> > Apparently, the problem appears on GCC-built RISC-V kernels with KASAN
> > enabled. In the previous message syzbot mentions
> > "riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU
> > Binutils for Debian) 2.35.2", but the issue also reproduces finely on
> > a newer GCC compiler: "riscv64-linux-gnu-gcc (Debian 11.2.0-10)
> > 11.2.0, GNU ld (GNU Binutils for Debian) 2.37".
> > For convenience, I also duplicate the .config file from the bot's
> > message: https://syzkaller.appspot.com/x/.config?x=522544a2e0ef2a7d
> >
> > Can someone with KASAN and RISC-V expertise please take a look?
>
> I'll take a look at that today.
>
> Thanks for reporting the issue,

Hi Alex,

Do you have any updates on this? This is still blocking syzbot:
https://syzkaller.appspot.com/bug?extid=330a558d94b58f7601be

Do you use KASAN with clang or gcc? We can't boot riscv kernel with neither.

[Alexandre Ghiti]

Hi Dmitry,

I took a quick look, not enough to fix it but I know the issue comes
from the inline instrumentation, I have no problem with the outline
instrumentation. I need to find some cycles to work on this, my goal is
to fix this for 5.17.

Sorry about the delay,

Alex

>
>
>>> --
>>> Best Regards,
>>> Aleksandr
>>>
>>>
>>> On Tue, Jan 18, 2022 at 11:26 AM syzbot
>>> <syzbot+330a55...@syzkaller.appspotmail.com> wrote:
>>>> Hello,
>>>>
>>>> syzbot found the following issue on:
>>>>
>>>> HEAD commit: f6f7fbb89bf8 riscv: dts: sifive unmatched: Link the tmp451..
>>>> 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=1095f85bb00000
>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=522544a2e0ef2a7d
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=330a558d94b58f7601be
>>>> compiler: riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>>>> userspace arch: riscv64
>>>>
>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>> Reported-by: syzbot+330a55...@syzkaller.appspotmail.com

> _______________________________________________
> linux-riscv mailing list
> linux...@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

[Aleksandr Nogikh]

Hi Alex,

Thanks for the update!

Can you please share the .config with which you tested the outline
instrumentation?
I updated the syzbot config to use KASAN_OUTLINE instead of KASAN_INLINE,
but it still does not boot :(

Here's what I used:
https://gist.github.com/a-nogikh/279c85c2d24f47efcc3e865c08844138

--
Best Regards,
Aleksandr

>
> Sorry about the delay,
>
> Alex
>
>
> >
> >
> >>> --
> >>> Best Regards,
> >>> Aleksandr
> >>>
> >>>
> >>> On Tue, Jan 18, 2022 at 11:26 AM syzbot
> >>> <syzbot+330a55...@syzkaller.appspotmail.com> wrote:
> >>>> Hello,
> >>>>
> >>>> syzbot found the following issue on:
> >>>>
> >>>> HEAD commit: f6f7fbb89bf8 riscv: dts: sifive unmatched: Link the tmp451..
> >>>> 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=1095f85bb00000
> >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=522544a2e0ef2a7d
> >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=330a558d94b58f7601be
> >>>> compiler: riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> >>>> userspace arch: riscv64
> >>>>
> >>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >>>> Reported-by: syzbot+330a55...@syzkaller.appspotmail.com
> > _______________________________________________
> > linux-riscv mailing list
> > linux...@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>

> --
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[Aleksandr Nogikh]

Update: it doesn't boot with that big config, but boots if I generate
a simple one with KASAN_OUTLINE:

make defconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-
./scripts/config -e KASAN -e KASAN_OUTLINE
make olddefconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-

And it indeed doesn't work if I use KASAN_INLINE.

[Dmitry Vyukov]

It may be an issue with code size. Full syzbot config + KASAN + KCOV
produce hugely massive .text. It may be hitting some limitation in the
bootloader/kernel bootstrap code.

[Aleksandr Nogikh]

I bisected the difference between the config we use on syzbot and the
simple one that was generated like I described above.
Turns out that it's the DEBUG_VIRTUAL config that makes the difference.

make defconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-
./scripts/config -e KASAN -e KASAN_OUTLINE -e DEBUG_VIRTUAL
make olddefconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-

And the resulting kernel does not boot.
My env: the `riscv/fixes` branch, commit
6df2a016c0c8a3d0933ef33dd192ea6606b115e3, qemu 6.2.0.

[Aleksandr Nogikh]

If I use just defconfig + DEBUG_VIRTUAL, without any KASAN, it begins
to boot, but overwhelms me with tons of `virt_to_phys used for
non-linear address:` errors.

Like that

[ 2.701271] virt_to_phys used for non-linear address:
00000000b59e31b6 (0xffffffff806c2000)
[ 2.701727] WARNING: CPU: 0 PID: 1 at arch/riscv/mm/physaddr.c:16
__virt_to_phys+0x7e/0x86
[ 2.702207] Modules linked in:
[ 2.702393] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W
5.17.0-rc1 #1
[ 2.702806] Hardware name: riscv-virtio,qemu (DT)
[ 2.703051] epc : __virt_to_phys+0x7e/0x86
[ 2.703298] ra : __virt_to_phys+0x7e/0x86
[ 2.703547] epc : ffffffff80008448 ra : ffffffff80008448 sp :
ffff8f800021bde0
[ 2.703977] gp : ffffffff80ed9b30 tp : ffffaf8001230000 t0 :
ffffffff80eea56f
[ 2.704704] t1 : ffffffff80eea560 t2 : 0000000000000000 s0 :
ffff8f800021be00
[ 2.705153] s1 : ffffffff806c2000 a0 : 000000000000004f a1 :
ffffffff80e723d8
[ 2.705555] a2 : 0000000000000010 a3 : fffffffffffffffe a4 :
0000000000000000
[ 2.706027] a5 : 0000000000000000 a6 : 0000000000000005 a7 :
ffffffffffffffff
[ 2.706474] s2 : ffffffff80b80b08 s3 : 00000000000000c2 s4 :
ffffffff806c2000
[ 2.706891] s5 : ffffffff80edba10 s6 : ffffffff80edb960 s7 :
0000000000000001
[ 2.707290] s8 : 00000000000000ff s9 : ffffffff80b80b40 s10:
00000000000000cc
[ 2.707689] s11: ffffaf807e1fcf00 t3 : 0000000000000076 t4 :
ffffffffffffffff
[ 2.708092] t5 : 00000000000001f2 t6 : ffff8f800021bb48
[ 2.708433] status: 0000000000000120 badaddr: 0000000000000000
cause: 0000000000000003
[ 2.708919] [<ffffffff8011416a>] free_reserved_area+0x72/0x19a
[ 2.709296] [<ffffffff80003a5a>] free_initmem+0x6c/0x7c
[ 2.709648] [<ffffffff805f60c8>] kernel_init+0x3a/0x10a
[ 2.709993] [<ffffffff80002fda>] ret_from_exception+0x0/0xc
[ 2.710310] ---[ end trace 0000000000000000 ]---

[Alexandre Ghiti]

First, thank you for working on this.

I was able to reproduce this: the first one regarding init_zero_pfn is
legit but not wrong, I have to check when it was introduced and how to
fix this.
Regarding the huge batch that follows, at first sight, I would say
this is linked to my sv48 patchset but that does not seem important as
the address is a kernel mapping address so the use of virt_to_phys is
right.

I took a quick glance and it traps on a KASAN address that is not
mapped, either because it is too soon or because the mapping failed
somehow.

I'll definitely dive into that tomorrow, sorry for being slow here and
thanks again for all your work, that helps a lot.

Thanks,

Alex

[Alexandre Ghiti]

Aleksandr,

I fixed a few things today: KASAN + SPARSE_VMEMMAP, DEBUG_VIRTUAL and
maybe KASAN + KCOV.

With those small fixes, I was able to boot your large dotconfig with
KASAN_OUTLINE, the inline version still fails, this is my next target
:)
I'll push that tomorrow!

Thanks again,

Alex

[Aleksandr Nogikh]

Hi Alex,

On Thu, Feb 17, 2022 at 5:53 PM Alexandre Ghiti

Awesome, thank you very much!
Looking forward to finally seeing the instance run :)

--
Best Regards,
Aleksandr

>
> Thanks again,
>
> Alex

[Alexandre Ghiti]

Hi Aleksandr,

I sent a patchset which should fix your config with *outline* instrumentation.

However, as you'll see in the cover letter, I have an issue with
another KASAN config and if you can take a look at the stacktrace and
see if that rings a bell, that would be great.

Don't hesitate next time to ping me when the riscv syzbot instance fails :)

Alex

[Aleksandr Nogikh]

Hi Alex,

On Fri, Feb 18, 2022 at 2:45 PM Alexandre Ghiti

Thank you very much for the patch series and for the update!

I'll try to take a closer look on Monday. To be honest, I don't really
have expertise in KASAN internals, so it's rather unlikely that I
could be of much help here :(

>
> >
> > --
> > Best Regards,
> > Aleksandr
> >
> > >
> > > Thanks again,
> > >
> > > Alex
>

> --
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[Dmitry Vyukov]

On Fri, 18 Feb 2022 at 14:45, Alexandre Ghiti

Was this fix merged? The riscv instance still does not boot:
https://syzkaller.appspot.com/bug?id=5f2ff52ad42cba9f222202219baebd4e63e35127

> However, as you'll see in the cover letter, I have an issue with
> another KASAN config and if you can take a look at the stacktrace and
> see if that rings a bell, that would be great.
>
> Don't hesitate next time to ping me when the riscv syzbot instance fails :)
>
> Alex
>
>
> >
> > --
> > Best Regards,
> > Aleksandr
> >
> > >
> > > Thanks again,
> > >
> > > Alex
>

> --
> You received this message because you are subscribed to the Google Groups "kasan-dev" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+...@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/CA%2BzEjCtB0rTuNAJkrM2q3JQL7D-9fAXBo0Ud0w__gy9CAfo_Ag%40mail.gmail.com.

[Alexandre Ghiti]

Yes it has been in Linus tree since 5.18-rc1. I'll take a look at that
this week.

Thanks,

Alex

[Atish Patra]

Are you seeing this error or a different one ? I used the
syzkaller_defconfig from the patch below on v5.18.

https://lore.kernel.org/all/2022041917495...@rivosinc.com/

[ 15.076116][ T1] Mandatory Access Control activated.
[ 15.158241][ T1] AppArmor: AppArmor Filesystem Enabled
[ 16.150870][ T1] NET: Registered PF_INET protocol family
[ 16.166167][ T1] IP idents hash table entries: 32768 (order: 6,
262144 bytes, linear)
[ 16.188727][ T1] Unable to handle kernel paging request at
virtual address ffebfffeffff2000
[ 16.192727][ T1] Oops [#1]
[ 16.193479][ T1] Modules linked in:
[ 16.194687][ T1] CPU: 3 PID: 1 Comm: swapper/0 Not tainted
5.18.0-00001-g37ac279268bf-dirty #9
[ 16.196486][ T1] Hardware name: riscv-virtio,qemu (DT)
[ 16.197836][ T1] epc : kasan_check_range+0x9e/0x14e
[ 16.199104][ T1] ra : memset+0x1e/0x4c
[ 16.200091][ T1] epc : ffffffff804787e0 ra : ffffffff80478f30 sp
: ff600000073ffb70
[ 16.201420][ T1] gp : ffffffff85879e80 tp : ff600000073f0000 t0
: 7300000000000000
[ 16.202762][ T1] t1 : ffebfffeffff21ff t2 : 73746e6564692050 s0
: ff600000073ffba0
[ 16.204047][ T1] s1 : 0000000000001000 a0 : ffebfffeffff2200 a1
: 0000000000001000
[ 16.205312][ T1] a2 : 0000000000000001 a3 : ffffffff803a4f32 a4
: ff5ffffffff90000
[ 16.206592][ T1] a5 : ffebfffeffff2000 a6 : 0000004000000000 a7
: ff5ffffffff90fff
[ 16.207865][ T1] s2 : ff5ffffffff90000 s3 : 0000000000000000 s4
: ffffffff8467ea90
[ 16.209134][ T1] s5 : 0000000000000000 s6 : ff5ffffffff90000 s7
: 0000000000000000
[ 16.210394][ T1] s8 : 0000000000001000 s9 : ffffffff8587ca40
s10: 0000000000000004
[ 16.211952][ T1] s11: ffffffff858a03a0 t3 : 0000000000000000 t4
: 0000000000000040
[ 16.213469][ T1] t5 : ffebfffeffff2200 t6 : ff600000073ff738
[ 16.214853][ T1] status: 0000000200000120 badaddr:
ffebfffeffff2000 cause: 000000000000000d
[ 16.216910][ T1] Call Trace:
[ 16.217816][ T1] [<ffffffff803a4f32>] pcpu_alloc+0x844/0x1254
[ 16.219110][ T1] [<ffffffff803a59a0>] __alloc_percpu+0x28/0x34
[ 16.220244][ T1] [<ffffffff8328824a>] ip_rt_init+0x17e/0x382
[ 16.221606][ T1] [<ffffffff8328861c>] ip_init+0x18/0x30
[ 16.222719][ T1] [<ffffffff8328a0ee>] inet_init+0x2a6/0x550
[ 16.223863][ T1] [<ffffffff80003204>] do_one_initcall+0x130/0x7dc
[ 16.225002][ T1] [<ffffffff83201fbc>] kernel_init_freeable+0x510/0x5b4
[ 16.226273][ T1] [<ffffffff8319842a>] kernel_init+0x28/0x21c
[ 16.227337][ T1] [<ffffffff80005818>] ret_from_exception+0x0/0x10
[ 16.229910][ T1] ---[ end trace 0000000000000000 ]---
[ 16.231880][ T1] Kernel panic - not syncing: Fatal exception

> Thanks,
>
> Alex
>
>
> >
> >> However, as you'll see in the cover letter, I have an issue with
> >> another KASAN config and if you can take a look at the stacktrace and
> >> see if that rings a bell, that would be great.
> >>
> >> Don't hesitate next time to ping me when the riscv syzbot instance fails :)
> >>
> >> Alex
> >>
> >>
> >>> --
> >>> Best Regards,
> >>> Aleksandr
> >>>
> >>>> Thanks again,
> >>>>
> >>>> Alex
> >> --
> >> You received this message because you are subscribed to the Google Groups "kasan-dev" group.
> >> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+...@googlegroups.com.
> >> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/CA%2BzEjCtB0rTuNAJkrM2q3JQL7D-9fAXBo0Ud0w__gy9CAfo_Ag%40mail.gmail.com.
>

> _______________________________________________
> linux-riscv mailing list
> linux...@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv



--

Regards,
Atish

[Atish Patra]

Enabling CONFIG_KASAN_VMALLOC=y solves the issue and I am able to boot
to the userspace.
I have tried enabling/disabling CONFIG_VMAP_STACK as well. Both works fine.

Looking at the ARM64 Kconfig, KASAN_VMALLOC is enabled if KASAN is enabled.
This diff seems to work for me.
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 00fd9c548f26..cbf0fe227c77 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -122,6 +122,7 @@ config RISCV
select TRACE_IRQFLAGS_SUPPORT
select UACCESS_MEMCPY if !MMU
select ZONE_DMA32 if 64BIT
+ select KASAN_VMALLOC if KASAN

I am not a kasan expert so I am not sure if this is the correct fix or
just hides the real issue. pcpu_alloc seems to use vmalloc though.

> > Thanks,
> >
> > Alex
> >
> >
> > >
> > >> However, as you'll see in the cover letter, I have an issue with
> > >> another KASAN config and if you can take a look at the stacktrace and
> > >> see if that rings a bell, that would be great.
> > >>
> > >> Don't hesitate next time to ping me when the riscv syzbot instance fails :)
> > >>
> > >> Alex
> > >>
> > >>
> > >>> --
> > >>> Best Regards,
> > >>> Aleksandr
> > >>>
> > >>>> Thanks again,
> > >>>>
> > >>>> Alex
> > >> --
> > >> You received this message because you are subscribed to the Google Groups "kasan-dev" group.
> > >> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+...@googlegroups.com.
> > >> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/CA%2BzEjCtB0rTuNAJkrM2q3JQL7D-9fAXBo0Ud0w__gy9CAfo_Ag%40mail.gmail.com.
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux...@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>
>
>
> --
> Regards,
> Atish

--
Regards,
Atish

[Dmitry Vyukov]

Hi Atish,

Enabling KASAN_VMALLOC in syzbot config actually makes it boot for me!
It's probably good to enforce it and/or give better diagnostics and/or
fix KASAN w/o KASAN_VMALLOC, but I've sent a fix up for syzbot config
for now:
https://github.com/google/syzkaller/pull/3167
Thanks for looking into it.

[Alexandre Ghiti]

Hi Atish,

When this type of thing happens, generally this is because of an error
in the kasan page table, I'll take a look this time, sorry I did not
do this before.

Thanks for finding this,

Alex

[Dmitry Vyukov]

On Fri, 27 May 2022 at 09:33, Alexandre Ghiti
<alexand...@canonical.com> wrote:
>
> Hi Atish,

Unfortunately riscv still does not work for syzbot, other bugs piled up.
Something has changes wrt user-space pointers:
https://groups.google.com/g/syzkaller-bugs/c/lU0GQTZoNQQ/m/iuRBTgU3AAAJ
https://syzkaller.appspot.com/bug?extid=2c5da6a0a16a0c4f34aa

[Atish Patra]

On Fri, May 27, 2022 at 12:33 AM Alexandre Ghiti

No worries. But the above diff is applicable anyways. Correct ?

--
Regards,
Atish

[Alexandre Ghiti]

Yes, we can use that until I fix the underlying issue.

[syzbot]

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