linux-kernel - Re: [PATCH 3/9] x86/entry/32: fix the end of the stack for newly forked tasks

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Date:   Wed, 21 Sep 2016 06:35:16 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Nilay Vaish <nilayvaish@...il.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3/9] x86/entry/32: fix the end of the stack for newly
 forked tasks

On Tue, Sep 20, 2016 at 11:39:35PM -0700, Andy Lutomirski wrote:
> > And the ia64 entry code has some similar language:
> >
> >                 /*
> >                  * Invoke schedule_tail(task) while preserving in0-in7, which may be needed
> >                  * in case a system call gets restarted.
> >                  */
> >         GLOBAL_ENTRY(ia64_invoke_schedule_tail)
> >                 ...
> 
> That comment has to be wrong.  What syscall could possibly be
> restarted across schedule_tail()?  It's a brand new thread and has
> literally never done a syscall.

Hm, yeah, that comment doesn't make any sense.

> There may be another reason that the registers are live there, but I
> generally do my best to never look at ia64 asm code.

Yeah, I'm just going to turn around, pretend I never saw it, and slowly
walk away...

-- 
Josh