linux-kernel - Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read

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Message-ID: <20151006201915.GV3910@linux.vnet.ibm.com>
Date:	Tue, 6 Oct 2015 13:19:15 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of
 __srcu_read_lock()

On Tue, Oct 06, 2015 at 10:07:25PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 06, 2015 at 09:13:42AM -0700, Paul E. McKenney wrote:
> > Currently, __srcu_read_lock() cannot be invoked from restricted
> > environments because it contains calls to preempt_disable() and
> > preempt_enable(), both of which can invoke lockdep, which is a bad
> > idea in some restricted execution modes.  This commit therefore moves
> > the preempt_disable() and preempt_enable() from __srcu_read_lock()
> > to srcu_read_lock().  It also inserts the preempt_disable() and
> > preempt_enable() around the call to __srcu_read_lock() in do_exit().
> 
> Did you not simply want to use: preempt_disable_notrace() ?

I believe that tracing the preempt_disable() in srcu_read_lock() and
srcu_read_unlock() is actually a good thing.  Or am I missing your
point?

							Thanx, Paul

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