Re: selftests: ftrace: Internal error: Oops: sve_save_state

On Tue, 17 Oct 2023 at 17:52, Mark Brown [off-list ref] wrote:

On Tue, Oct 17, 2023 at 01:34:18PM +0530, Naresh Kamboju wrote:

quoted

Following kernel crash noticed while running selftests: ftrace:
ftracetest-ktap on FVP models running stable-rc 6.5.8-rc2.

quoted

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.

quoted

[  764.987161] Unable to handle kernel NULL pointer dereference at
virtual address 0000000000000000

quoted

[  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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel