linux-kernel - Re: RCU: how to suppress warnings from rcu_assign

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Message-ID: <1312188453.2719.1.camel@edumazet-laptop>
Date:	Mon, 01 Aug 2011 10:47:33 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	David Miller <davem@...emloft.net>, shemminger@...tta.com,
	mchan@...adcom.com, linux-kernel@...r.kernel.org
Subject: Re: RCU: how to suppress warnings from rcu_assign_pointer?

Le dimanche 31 juillet 2011 à 22:23 -0700, Paul E. McKenney a écrit :
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> rcu: Make rcu_assign_pointer() unconditionally insert a memory barrier
> 
> Recent changes to gcc give warning messages on rcu_assign_pointers()'s
> checks that allow it to determine when it is OK to omit the memory
> barrier.  Stephen Hemminger tried a number of gcc tricks to silence
> this warning, but #pragmas and CPP macros do not work together in the
> way that would be required to make this work.
> 
> However, we now have RCU_INIT_POINTER(), which already omits this
> memory barrier, and which therefore may be used when assigning NULL to
> an RCU-protected pointer that is accessible to readers.  This commit
> therefore makes rcu_assign_pointer() unconditionally emit the memory
> barrier.
> 
> Reported-by: Stephen Hemminger <shemminger@...tta.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> Acked-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>  

Sure Paul, thanks for doing this. I have _very_ limited access to
Internet this week.

Eric


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