linux-kernel - Re: WARNING: Kernel stack regs has bad 'bp' value

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Date:   Fri, 11 Sep 2020 10:14:41 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: WARNING: Kernel stack regs has bad 'bp' value



On 2020-09-11 10:00 a.m., Josh Poimboeuf wrote:
> Hi Logan,
> 
> Thanks for the bug report.  (Sorry I missed the first one, Naresh.)
> 
> The problem is that ret_from_fork() is no longer in .entry.text, so the
> following check in the FP unwinder doesn't work when ret_from_fork()
> gets interrupted.
> 
> 	/*
> 	 * Don't warn if the unwinder got lost due to an interrupt in entry
> 	 * code or in the C handler before the first frame pointer got set up:
> 	 */
> 	if (state->got_irq && in_entry_code(state->ip))
> 		goto the_end;
> 
> If you have the ability to recreate, can you try the following patch?

Sorry, but I can not reliably hit this bug. I hit it randomly twice last
week however, despite doing a bunch more runs this week, I haven't hit
it again.

I can add the patch to my testing next week but I ca not give you a
definitive answer on whether this fixes the bug.

Perhaps Naresh's test is a better reproducer.

Thanks!

Logan