On Wed, Oct 07, 2015 at 09:20:38AM +0200, Peter Zijlstra wrote:
> On Tue, Oct 06, 2015 at 02:03:48PM -0700, Paul E. McKenney wrote:
> > On Tue, Oct 06, 2015 at 10:32:24PM +0200, Peter Zijlstra wrote:
> > > On Tue, Oct 06, 2015 at 01:19:15PM -0700, Paul E. McKenney wrote:
> > > > 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?
> > >
> > > Depends a bit on why we needed this change in the first place -- which,
> > > going by the other branch of this thread, seems lost. However,
> > > preempt_{dis,en}able_notrace() will not end up in any tracer/lockdep and
> > > generate the minimum code that preserves the required semantics.
> >
> > True enough! But can all architectures locate the TIF in all contexts?
>
> They had better, otherwise we have a problem with NMIs touching it :-)
Fair enough! ;-)
Thanx, Paul
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