From mboxrd@z Thu Jan  1 00:00:00 1970
From: paulmck@linux.vnet.ibm.com (Paul E. McKenney)
Date: Fri, 4 Dec 2015 08:07:06 -0800
Subject: [PATCH] arm64: spinlock: serialise spin_unlock_wait against
 concurrent lockers
In-Reply-To: <20151204092110.GE17308@twins.programming.kicks-ass.net>
References: <1448624646-15863-1-git-send-email-will.deacon@arm.com>
 <20151130155839.GK17308@twins.programming.kicks-ass.net>
 <20151201164035.GE27751@arm.com>
 <20151203001141.GO28602@linux.vnet.ibm.com>
 <20151203132839.GA3816@twins.programming.kicks-ass.net>
 <20151203163243.GI11337@arm.com>
 <20151203172207.GR28602@linux.vnet.ibm.com>
 <20151204092110.GE17308@twins.programming.kicks-ass.net>
Message-ID: <20151204160706.GC28602@linux.vnet.ibm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Dec 04, 2015 at 10:21:10AM +0100, Peter Zijlstra wrote:
> On Thu, Dec 03, 2015 at 09:22:07AM -0800, Paul E. McKenney wrote:
> > >   2. Only PowerPC is going to see the (very occassional) failures, so
> > >      testing this is nigh on impossible :(
> > 
> > Indeed, we clearly cannot rely on normal testing, witness rcutorture
> > failing to find the missing smp_mb__after_unlock_lock() instances that
> > Peter found by inspection.  So I believe that augmented testing is
> > required, perhaps as suggested above.
> 
> To be fair, those were in debug code and non critical for correctness
> per se. That is, at worst the debug print would've observed an incorrect
> value.

True enough, but there is still risk from people repurposing debug code
for non-debug uses.  Still, thank you, I don't feel -quite- so bad about
rcutorture's failure to find these.  ;-)

							Thanx, Paul