linux-kernel - Re: selftests: ftrace: Internal error: Oops: sve_save

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Message-ID: <ad5b7442-385d-41db-9202-a36414460610@sirena.org.uk>
Date:   Tue, 17 Oct 2023 13:22:14 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org,
        linux-stable <stable@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Marc Zyngier <maz@...nel.org>
Subject: Re: selftests: ftrace: Internal error: Oops: sve_save_state

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?

> [  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?

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