From: Davidlohr Bueso <dave@stgolabs.net>
To: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
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 10:02:39 -0800 [thread overview]
Message-ID: <20160205180239.GB12375@linux-uzut.site> (raw)
In-Reply-To: <20160205094441.GB7551@gmail.com>
On Fri, 05 Feb 2016, Ingo Molnar wrote:
>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.
Sure, fair enough.
>
>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.
Right, but we do in fact use smp barriers in this cases in the real code, that mb() is
just in the comments, I guess it would be desirable to change it to smp_mb nonetheless.
However, could these changes be in a followup? Mainly because the barrier B references
will be updated across all futex.c... unless there are still concerns about this particular
patch, of course.
Thanks,
Davidlohr
next prev parent reply other threads:[~2016-02-05 18:02 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
2016-02-05 18:02 ` Davidlohr Bueso [this message]
2016-02-06 8:22 ` Ingo Molnar
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