linux-kernel - Re: [PATCH][RFC] fix kernel BUG at mm/migrate.c:719! in 2.6.26-rc5-mm3

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Message-Id: <20080618134128.828156bc.nishimura@mxp.nes.nec.co.jp>
Date:	Wed, 18 Jun 2008 13:41:28 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org
Subject: Re: [PATCH][RFC] fix kernel BUG at mm/migrate.c:719! in
 2.6.26-rc5-mm3

On Wed, 18 Jun 2008 10:54:00 +0900, Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> On Wed, 18 Jun 2008 00:33:18 +0900, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> > > @@ -715,13 +725,7 @@ unlock:
> > >   		 * restored.
> > >   		 */
> > >   		list_del(&page->lru);
> > > -		if (!page->mapping) {
> > > -			VM_BUG_ON(page_count(page) != 1);
> > > -			unlock_page(page);
> > > -			put_page(page);		/* just free the old page */
> > > -			goto end_migration;
> > > -		} else
> > > -			unlock = putback_lru_page(page);
> > > +		unlock = putback_lru_page(page);
> > >  	}
> > >  
> > >  	if (unlock)
> > 
> > this part is really necessary?
> > I tryed to remove it, but any problem doesn't happend.
> > 
> I made this part first, and added a fix for migration_entry_wait later.
> 
> So, I haven't test without this part, and I think it will cause
> VM_BUG_ON() here without this part.
> 
> Anyway, I will test it.
> 
I got this VM_BUG_ON() as expected only by doing:

  # echo $$ >/cgroup/cpuset/02/tasks

So, I beleive that both fixes for migration_entry_wait and
unmap_and_move (and, of course, removal VM_BUG_ON from
putback_lru_page) are needed.


Thanks,
Daisuke Nishimura.
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