linux-kernel - Re: [GIT] Sparc

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Date:	Wed, 22 Sep 2010 21:43:24 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>, akpm@...ux-foundation.org,
	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT] Sparc

On Wed, Sep 22, 2010 at 08:53:49PM +0100, Al Viro wrote:
> On Wed, Sep 22, 2010 at 12:08:53PM -0700, Linus Torvalds wrote:
> > On Wed, Sep 22, 2010 at 11:53 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
> > >
> > > Um, no. ?You've *already* called get_signal_to_deliver(). ?There had been
> > > no SIGSEGV in sight. ?You happily went on to set a sigframe for e.g.
> > > SIGHUP, but ran out of stack. ?At that point you get force_sigsegv()
> > > from handle_signal(). ?_NOW_ you have a pending SIGSEGV
> > 
> > Ahh. Ok. Different case from the one I thought you were worried about.
> > And yeah, I guess that one does require us to mess with the low-level
> > asm code (although I do wonder if we could not make the whole
> > do_notify_resume + reschedule code be generic C code - it's a lot of
> > duplicated subtle asm as it is).
> 
> Worse than just that...  Note that on sparc you need to deal with
> fault_in_user_windows(), which can also trigger signals.

	Actually, I wonder why don't we do the following:
1) check wsaved first, do fault_in_user_windows() if needed (and probably do
Something Cruel(tm) if we fail copy_to_user() in there)
2) in a loop check if we need to reschedule / if we need to handle signals
3) don't bother with wsaved checks in setup_frame() variants at all -
wsaved can't grow back at that point; we also can use flush_user_windows()
instead of full synchronize_user_stack() in there.

It's definitely a separate patch, but it looks like it might be worth
doing...  Comments?
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