linux-kernel - Re: [PATCH RFC] rcu: Make __rcu_read

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Message-ID: <20120327163902.GQ2450@linux.vnet.ibm.com>
Date:	Tue, 27 Mar 2012 09:39:03 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH RFC] rcu: Make __rcu_read_lock() inlinable

On Tue, Mar 27, 2012 at 08:26:07AM -0400, Steven Rostedt wrote:
> On Mon, 2012-03-26 at 22:15 -0700, Paul E. McKenney wrote:
> 
> > Hmmm...  I am not yet sure whether it is easier to make RCU use legal
> > in switch_to() or to detect it.  I am inclined to take whatever course
> > is easiest, which is likely to make it legal.  :-/
> 
> We could just declare that we do not allow tracepoints in arch specific
> "switch_to" code. Then you shouldn't need to worry about RCU in
> switch_to().

Heh.  I expect that to work about as well as the earlier declaration
that RCU not be used in the idle loop.  ;-)

> sched_rcu can still work there correct? That is, a synchronize_sched()
> should not be affected. As that is needed for the function tracing, and
> that may be called within a switch_to.

Yep, good point.

							Thanx, Paul

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