selftests: ftrace: Internal error: Oops: sve_save_state

[Naresh Kamboju]

On Tue, 17 Oct 2023 at 17:52, Mark Brown <broonie at kernel.org> wrote:
>
> On Tue, Oct 17, 2023 at 01:34:18PM +0530, Naresh Kamboju wrote:
>
> > Following kernel crash noticed while running selftests: ftrace:
> > ftracetest-ktap on FVP models running stable-rc 6.5.8-rc2.
>
> > This is not an easy to reproduce issue and not seen on mainline and next.
> > We are investigating this report.
>
> To confirm have you seen this on other stables as well or is this only
> v6.5?  For how long have you been seeing this?

This is only seen on 6.5.8-rc2 and seen only once.
I have checked on mainline / next and other stable branches and this crash
is not seen anywhere else.

However, I will keep checking them on other branches and next and mainline.

>
> > [  764.987161] Unable to handle kernel NULL pointer dereference at
> > virtual address 0000000000000000
>
> > [  765.074221] Call trace:
> > [  765.075045]  sve_save_state+0x4/0xf0
> > [  765.076138]  fpsimd_thread_switch+0x2c/0xe8
> > [  765.077305]  __switch_to+0x20/0x158
> > [  765.078384]  __schedule+0x2cc/0xb38
> > [  765.079464]  preempt_schedule_irq+0x44/0xa8
> > [  765.080633]  el1_interrupt+0x4c/0x68
> > [  765.081691]  el1h_64_irq_handler+0x18/0x28
> > [  765.082829]  el1h_64_irq+0x64/0x68
> > [  765.083874]  ftrace_return_to_handler+0x98/0x158
> > [  765.085090]  return_to_handler+0x20/0x48
> > [  765.086205]  do_sve_acc+0x64/0x128
> > [  765.087272]  el0_sve_acc+0x3c/0xa0
> > [  765.088356]  el0t_64_sync_handler+0x114/0x130
> > [  765.089524]  el0t_64_sync+0x190/0x198
>
> So something managed to get flagged as having SVE state without having
> the backing storage allocated.  We *were* preempted in the SVE access
> handler which does the allocation but I can't see the path that would
> trigger that since we allocate the state before setting TIF_SVE.  It's
> possible the compiler did something funky, a decode of the backtrace
> might help show that?

We have not uploaded vmlinux and System.map to this specific build.
However, I have requested to have these files get uploaded for upcoming
builds.

- Naresh