From: Ingo Molnar <mingo@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
Mel Gorman <mgorman@techsingularity.net>,
Peter Zijlstra <peterz@infradead.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: Fri, 5 Feb 2016 10:44:42 +0100 [thread overview]
Message-ID: <20160205094441.GB7551@gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1602041845280.25254@nanos>
* Thomas Gleixner <tglx@linutronix.de> wrote:
> 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.
So I too didn't understand that sentence at first, because the capitalization
really throws off quick parsing of that comment, as 'MB' ususally denotes
megabytes.
So please change it to "mb(); (A)" or so - and I think all of these comments
should be changed to use a standard API name for the barrier they imply, as the
head of futex.c does:
* waiters++; (a)
* mb(); (A) <-- paired with -.
* |
* lock(hash_bucket(futex)); |
* |
* uval = *futex; |
* | *futex = newval;
* | sys_futex(WAKE, futex);
* | futex_wake(futex);
* |
* `-------> mb(); (B)
Btw., pedantic: shouldn't that be smp_mb()? Futexes don't operate on IO spaces, so
on UP they only need compiler barriers.
Thanks,
Ingo
next prev parent reply other threads:[~2016-02-05 9:44 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
2016-02-05 9:44 ` Ingo Molnar [this message]
2016-02-05 18:02 ` Davidlohr Bueso
2016-02-06 8:22 ` Ingo Molnar
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