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From: Ingo Molnar <mingo@elte.hu>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Valdis.Kletnieks@vt.edu,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: 2.6.39-rc6-mmotm0506 - lockdep splat in RCU code on page fault
Date: Tue, 10 May 2011 10:57:46 +0200	[thread overview]
Message-ID: <20110510085746.GG27426@elte.hu> (raw)
In-Reply-To: <20110510082029.GF2258@linux.vnet.ibm.com>


* Paul E. McKenney <paulmck@linux.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

WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo@elte.hu>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Valdis.Kletnieks@vt.edu,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: 2.6.39-rc6-mmotm0506 - lockdep splat in RCU code on page fault
Date: Tue, 10 May 2011 10:57:46 +0200	[thread overview]
Message-ID: <20110510085746.GG27426@elte.hu> (raw)
In-Reply-To: <20110510082029.GF2258@linux.vnet.ibm.com>


* Paul E. McKenney <paulmck@linux.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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  reply	other threads:[~2011-05-10  8:58 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-10  1:04 2.6.39-rc6-mmotm0506 - lockdep splat in RCU code on page fault Valdis.Kletnieks
2011-05-10  8:20 ` Paul E. McKenney
2011-05-10  8:20   ` Paul E. McKenney
2011-05-10  8:57   ` Ingo Molnar [this message]
2011-05-10  8:57     ` Ingo Molnar
2011-05-10 16:21     ` Paul E. McKenney
2011-05-10 16:21       ` Paul E. McKenney
2011-05-10 20:44       ` Ingo Molnar
2011-05-10 20:44         ` Ingo Molnar
2011-05-11  7:44         ` Paul E. McKenney
2011-05-11  7:44           ` Paul E. McKenney
2011-05-11 23:11   ` Valdis.Kletnieks
2011-05-12  9:47     ` Paul E. McKenney
2011-05-12  9:47       ` Paul E. McKenney
2011-05-12 16:05       ` Valdis.Kletnieks
2011-05-13  7:18         ` Paul E. McKenney
2011-05-13  7:18           ` Paul E. McKenney

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