From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 4ED535F0001 for ; Tue, 7 Apr 2009 16:17:08 -0400 (EDT) Date: Tue, 7 Apr 2009 22:17:08 +0200 From: Johannes Weiner Subject: Re: [PATCH] [8/16] POISON: Add various poison checks in mm/memory.c Message-ID: <20090407201708.GA4220@cmpxchg.org> References: <20090407509.382219156@firstfloor.org> <20090407151005.4E24B1D046D@basil.firstfloor.org> <20090407190330.GB3818@cmpxchg.org> <20090407193145.GU17934@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090407193145.GU17934@one.firstfloor.org> Sender: owner-linux-mm@kvack.org To: Andi Kleen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org List-ID: On Tue, Apr 07, 2009 at 09:31:45PM +0200, Andi Kleen wrote: > On Tue, Apr 07, 2009 at 09:03:30PM +0200, Johannes Weiner wrote: > > On Tue, Apr 07, 2009 at 05:10:05PM +0200, Andi Kleen wrote: > > > > > > Bail out early when poisoned pages are found in page fault handling. > > > Since they are poisoned they should not be mapped freshly > > > into processes. > > > > > > This is generally handled in the same way as OOM, just a different > > > error code is returned to the architecture code. > > > > > > Signed-off-by: Andi Kleen > > > > > > --- > > > mm/memory.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > Index: linux/mm/memory.c > > > =================================================================== > > > --- linux.orig/mm/memory.c 2009-04-07 16:39:39.000000000 +0200 > > > +++ linux/mm/memory.c 2009-04-07 16:39:39.000000000 +0200 > > > @@ -2560,6 +2560,10 @@ > > > goto oom; > > > __SetPageUptodate(page); > > > > > > + /* Kludge for now until we take poisoned pages out of the free lists */ > > > + if (unlikely(PagePoison(page))) > > > + return VM_FAULT_POISON; > > > + > > > > When memory_failure() hits a page still on the free list > > It won't free it then. Later on it will take it out of the free lists, > but that code is not written yet. > > > (!page_count()) then the get_page() in memory_failure() will trigger a > > VM_BUG. So either this check is unneeded or it should be > > So no bug > > get_page_unless_zero() in memory_failure()? > > That's not what this is handling. The issue is that sometimes > the process can still freeing it and we need to make sure it > never hits the free lists. I think we missed each other here. I wasn't talking about _why_ you take that reference -- that is clear. But I see these two possibilities: a) memory_failure() is called on a page on the free list, the get_page() will trigger a bug because the refcount is 0 b) if that is not possible, the above check is not needed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org