linux-kernel - Re: 2.6.39-rc6-mmotm0506 - lockdep splat in RCU code on page fault

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Date:	Tue, 10 May 2011 10:57:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Valdis.Kletnieks@...edu, Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: 2.6.39-rc6-mmotm0506 - lockdep splat in RCU code on page fault


* Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> -	raw_spin_lock_irqsave(&rnp->lock, flags);
> -	rnp->wakemask |= rdp->grpmask;
> -	raw_spin_unlock_irqrestore(&rnp->lock, flags);
> +	do {
> +		old = rnp->wakemask;
> +		new = old | rdp->grpmask;
> +	} while (cmpxchg(&rnp->wakemask, old, new) != old);

Hm, isnt this an inferior version of atomic_or_long() in essence?

Note that atomic_or_long() is x86 only, so a generic one would have to be 
offered too i suspect, atomic_cmpxchg() driven or so - which would look like 
the above loop.

Most architectures could offer atomic_or_long() i suspect.

Thanks,

	Ingo
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