On Fri, May 27, 2016 at 06:52:11PM +0200, Sebastian Andrzej Siewior wrote: > 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?
Yes, smp_store_release() is the most natural way to publish things like this. Note that rcu_assign_pointer() also switched to using that. See commit: 88c1863066cc ("rcu: Define rcu_assign_pointer() in terms of smp_store_release()") for detail on the difference.