linux-kernel - Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v5)

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Message-ID: <1264091529.31321.223.camel@gandalf.stny.rr.com>
Date:	Thu, 21 Jan 2010 11:32:09 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	tglx@...utronix.de, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	laijs@...fujitsu.com, dipankar@...ibm.com
Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
 barrier (v5)

On Thu, 2010-01-21 at 11:22 -0500, Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@...dmis.org) wrote:

> > You may also need spin_lock_irqsave, et al. variants too.
> 
> Yep, or we simply use the local_irq_save/restore separately. That could
> be a good idea given that only few specialized sites are affected.

If it gets used more often, then we need to consider RT. RT modifies
spin_lock_irqsave into a standard mutex that does not disable
interrupts. But if something does:

	local_irq_save(flags);
	spin_lock_mb(&lock);
	[...]

Then it will break RT (if lock is to be converted).

-- Steve


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