Re: [PATCH] x86: fix app crashes after SMP resume

From: Hugh Dickins <hugh@veritas.com>
To: Glauber Costa <glommer@gmail.com>
Cc: Glauber Costa <gcosta@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
	"Theodore Ts'o" <tytso@mit.edu>,
	"Carlos R. Mafra" <crmafra2@gmail.com>,
	"Rafael J. Wysocki" <rjw@sisk.pl>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: fix app crashes after SMP resume
Date: Tue, 13 May 2008 16:12:10 +0100 (BST)	[thread overview]
Message-ID: <Pine.LNX.4.64.0805131556340.28566@blonde.site> (raw)
In-Reply-To: <5d6222a80805130703n68018048se32e7feadea26dc4@mail.gmail.com>

On Tue, 13 May 2008, Glauber Costa wrote:
> On Tue, May 13, 2008 at 10:26 AM, Hugh Dickins <hugh@veritas.com> wrote:
> >
> >  +#ifdef CONFIG_X86_32
> >  +       while (low_mappings)
> >  +               cpu_relax();
> >  +       __flush_tlb_all();
> >  +#endif
> >  +
> 
> If possible, we don't want to introduce any more ifdefs. Should be
> better to do it openly, define low_mappings as always 0 for x86_64.

You're right, something like that (but avoiding the __flush_tlb_all
on x86_64) would have been nicer; never mind, now it's going forward,
I'll leave it as is.

A bigger improvement would be to cut out all that swapper_pg_dir
to and fro, needing a global TLB flush on all cpus for each cpu.
Just have an alternate pg_dir (often already there as swsusp_pg_dir)
to point cr3 at for the bootup (or maybe it needs to be vice versa).

But that's harder to get right, and involves wider changes and much
more testing than I could afford for the bugfix.  Plus I expect it's
on your radar if not already done.

Hugh