From: Thomas Gleixner <tglx@linutronix.de>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: Mel Gorman <mgorman@techsingularity.net>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Chris Mason <clm@fb.com>, Darren Hart <dvhart@linux.intel.com>,
Hugh Dickins <hughd@google.com>,
linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>,
Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v5] futex: Remove requirement for lock_page in get_futex_key
Date: Thu, 4 Feb 2016 18:50:07 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.11.1602041845280.25254@nanos> (raw)
In-Reply-To: <20160204174343.GA12375@linux-uzut.site>
On Thu, 4 Feb 2016, Davidlohr Bueso wrote:
> On Thu, 04 Feb 2016, Thomas Gleixner wrote:
>
> > On Wed, 3 Feb 2016, Davidlohr Bueso wrote:
> > > + * We are not calling into get_futex_key_refs() in file-backed
> > > + * cases, therefore a successful atomic_inc return below will
> > > + * guarantee that get_futex_key() will continue to imply MB
> > > (B).
> >
> > Can you please make that "MB (B)" part a bit more outstanding. I really had
> > to
> > search for it.
>
> Hmm as you know this is mostly explained at the begining of the file, and we
> sprinkle MB (B) around the code based on that description. So I'm a bit
> confused
> as to why you don't like like that comment.
The other "MB (B)" places are more outstanding. It did not spring in my eye
immideately. So it's a pure cosmetic issue.
> > > + */
> > > + if (WARN_ON_ONCE(!atomic_inc_not_zero(&inode->i_count))) {
> > > + rcu_read_unlock();
> > > + put_page(page);
> > > +
> > > + goto again;
> > > + }
> >
> > Don't we need
> >
> > smp_mb__after_atomic();
> >
> > here to make it a full barrier on all architectures?
>
> I had this initially but, as Peter mentioned, we get that barrier with the
> successful atomic_inc_not_zero call anyway. Or is it something else you had
> in mind?
Oh. I missed that comment from Peter. And yes, I missed that
atomic_inc_not_zero() already has the barrier in the success case. :(
Thanks,
tglx
next prev parent reply other threads:[~2016-02-04 17:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-04 6:28 [PATCH v5] futex: Remove requirement for lock_page in get_futex_key Davidlohr Bueso
2016-02-04 9:06 ` Thomas Gleixner
2016-02-04 17:43 ` Davidlohr Bueso
2016-02-04 17:50 ` Thomas Gleixner [this message]
2016-02-05 9:44 ` Ingo Molnar
2016-02-05 18:02 ` Davidlohr Bueso
2016-02-06 8:22 ` Ingo Molnar
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