linux-kernel - Re: [PATCH] futex: Ensure get_futex_key

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Date:	Sat, 18 Oct 2014 13:25:07 -0700
From:	Darren Hart <dvhart@...radead.org>
To:	Davidlohr Bueso <dave@...olabs.net>,
	Darren Hart <dvhart@...ux.intel.com>
CC:	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org,
	Matteo Franchin <Matteo.Franchin@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>
Subject: Re: [PATCH] futex: Ensure get_futex_key_refs() always implies a barrier



On October 18, 2014 3:19:50 PM CDT, Davidlohr Bueso <dave@...olabs.net> wrote:
>On Sat, 2014-10-18 at 14:32 -0500, Darren Hart wrote:
>> Which is not incomplete (lacking the explicit smp_mb()) added by this
>> patch. Perhaps the MB implementation of get_futex_key_refs() need not
>be
>> explicitly enumerated here?
>
>Agreed, how about this:
>
>diff --git a/kernel/futex.c b/kernel/futex.c
>index 21f7e41..7a0805a 100644
>--- a/kernel/futex.c
>+++ b/kernel/futex.c
>@@ -143,9 +143,8 @@
>  *
>* Where (A) orders the waiters increment and the futex value read
>through
>* atomic operations (see hb_waiters_inc) and where (B) orders the write
>- * to futex and the waiters read -- this is done by the barriers in
>- * get_futex_key_refs(), through either ihold or atomic_inc, depending
>on the
>- * futex type.
>+ * to futex and the waiters read -- this is done by the barriers for
>both
>+ * shared and private futexes in get_futex_key_refs().

Works for me.

-- 
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