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Date: Fri, 27 May 2016 18:52:11 +0200
From: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>, LKML <linux-kernel@vger.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Darren Hart <darren@dvhart.com>, Ingo Molnar <mingo@kernel.org>,
        Michael Kerrisk <mtk.manpages@googlemail.com>,
        Davidlohr Bueso <dave@stgolabs.net>, Chris Mason <clm@fb.com>,
        "Carlos O'Donell" <carlos@redhat.com>,
        Torvald Riegel <triegel@redhat.com>,
        Eric Dumazet <edumazet@google.com>
Subject: Re: [patch V2 2/7] futex: Hash private futexes per process
Message-ID: <20160527165211.GB28561@breakpoint.cc>
References: <20160505204230.932454245@linutronix.de>
 <20160505204353.973009518@linutronix.de>
 <20160519122148.GZ3192@twins.programming.kicks-ass.net>
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On 2016-05-19 14:21:48 [+0200], Peter Zijlstra wrote:
> > +static void futex_populate_hash(unsigned int hash_bits)
> > +{
…
> > +	raw_spin_lock(&mm->futex_hash.lock);
> > +	/* We might have raced with another task allocating the hash. */
> > +	if (!mm->futex_hash.hash) {
> > +		mm->futex_hash.hash_bits = hash_bits;
> > +		/*
> > +		 * Ensure that the above is visible before we store
> > +		 * the pointer.
> > +		 */
> > +		smp_wmb(); /* (A0) Pairs with (B) */
> > +		mm->futex_hash.hash = hb;
> 
> 		smp_store_release(&mm->futex_hash.hash, hb); ?

just to be clear: You suggest to use "smp_store_release()" instead
smp_wmb() followed by the assignment?

Sebastian