linux-kernel - Re: [patch] futex: Fix v4.6+ ltp futex

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Date:	Mon, 06 Jun 2016 15:46:06 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mel Gorman <mgorman@...e.de>, lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	kirill@...temov.name
Subject: Re: [patch] futex: Fix v4.6+ ltp futex_wait04 regression

On Mon, 2016-06-06 at 15:34 +0200, Mike Galbraith wrote:
> On Mon, 2016-06-06 at 15:07 +0200, Peter Zijlstra wrote:
> 
> > > @@ -654,12 +666,14 @@ get_futex_key(u32 __user *uaddr, int fsh
> > >  
> > >  > > 	> > 	> > key->both.offset |= FUT_OFF_INODE;
> > > /* inode-based key */
> > >  > > 	> > 	> > key->shared.inode = inode;
> > > -> > 	> > 	> > key->shared.pgoff =
> > > basepage_index(page);
> > > +> > 	> > 	> > key->shared.pgoff =
> > > basepage_index(pinned);
> > 
> > But this seems to be the actual fix;
> 
> Yup, the three 'pinned' lines alone work just fine.

I was going by what the code used to look like.

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
...
#else
        page_head = compound_head(page);
        if (page != page_head) {
                get_page(page_head);
                put_page(page);
        }
#endif

That all went away, but the pinned page that we used in the end was
stable until Mel's optimization landed, leaving me thinking I needed to
do both.  Hohum, close but no banana.

	-Mike