Date: Tue, 16 Feb 2010 11:23:32 +0100
From: Andi Kleen <andi@firstfloor.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>, "H. Peter Anvin" <hpa@zytor.com>,
       Roland McGrath <roland@redhat.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       linux-kernel@vger.kernel.org
Subject: Re: x86: get rid of the insane TIF_ABI_PENDING bit
Message-ID: <20100216102332.GL21783@one.firstfloor.org>
References: <20100215161752.GA19962@redhat.com> <4B799C3F.7010308@zytor.com> <20100215194123.96D49FC3@magilla.sf.frob.com> <4B79B202.5090006@zytor.com> <20100216101903.GA1057@redhat.com>
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On Tue, Feb 16, 2010 at 11:19:03AM +0100, Oleg Nesterov wrote:
> On 02/15, H. Peter Anvin wrote:
> >
> > On 02/15/2010 11:41 AM, Roland McGrath wrote:
> > > It affects whatever uses is_compat_task(), but I can't see anything
> > > where that matters except inside some particular syscall or for
> > > syscall restart after signals.
> >
> > FWIW, the origin of this is checkin
> > 4d9bc79cd28b779610d9590b3a96a28a0f64a25a (2.6.18-rc1), which somewhat
> > unhelpfully states "Make sure is_compat_task works early".  It doesn't
> > specify what the failure is if is_compat_task doesn't work early.
> 
> Perhaps Andi could explain us why this is needed,
> 
> > On
> > the other hand, it sure as heck seems better to set it and not need it
> > than the other way around.
> 
> Agreed, but otoh it is always good to understand the code. If we
> really have a reason for TS_COMPAT, a small comment can help other
> readers.

My memory is somewhat fuzzy on this one, but I think it was related
to VMA placement (probably for stack randomization or something like that)
This happens before the first call. I might be wrong on that.

There might also have been other is_compat_task checks in the exec init
path, so partly it was defensive programming.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.
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