linux-kernel - Re: linux-next ppc64: RCU mods cause __might

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Date:	Thu, 03 May 2012 07:20:15 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: linux-next ppc64: RCU mods cause __might_sleep BUGs

On Wed, 2012-05-02 at 13:25 -0700, Hugh Dickins wrote:
> Got it at last.  Embarrassingly obvious.  __rcu_read_lock() and
> __rcu_read_unlock() are not safe to be using __this_cpu operations,
> the cpu may change in between the rmw's read and write: they should
> be using this_cpu operations (or, I put preempt_disable/enable in the
> __rcu_read_unlock below).  __this_cpus there work out fine on x86,
> which was given good instructions to use; but not so well on PowerPC.
> 
> I've been running successfully for an hour now with the patch below;
> but I expect you'll want to consider the tradeoffs, and may choose a
> different solution.

Didn't Linus recently rant about these __this_cpu vs this_cpu nonsense ?

I thought that was going out..

Cheers,
Ben.


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