linux-kernel - Re: [PATCH 1/2] x86/dumpstack: on oops do not rewind stack for kthread

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Date:   Fri, 21 Oct 2016 10:05:08 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Andy Lutomirski <luto@...capital.net>,
        Roman Pen <roman.penyaev@...fitbricks.com>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Tejun Heo <tj@...nel.org>, X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86/dumpstack: on oops do not rewind stack for
 kthread

On Fri, 21 Oct 2016, Peter Zijlstra wrote:
> We need to preserve the entire struct kthread on the stack, kthread just
> abuses that pointer to stash an on-stack kthread descriptor. See
> kthread():
> 
>   current->vfork_done = &self.exited;
> 
> Its a horrible horrible thing kthread does. I suppose there might have
> been some intent by keeping that exited completion last in the
> structure, but *shudder*.
> 
> But yes, leaving enough stack to not clobber that might keep this horror
> show working.
> 
> ISTR talk about alternative schemes for this a long time ago, but I
> cannot recall :-(

The simplest solution would be to stick struct kthread into task_struct,
but that's bloat.

But we can allocate it seperately along with kthread_create_info. That's
pretty straight forward.

Thanks,

	tglx