Re: Patch "tracing: Fix check for cpu online when event is disabled" has been added to the 3.10-stable tree

[Luis Henriques <luis.henriques@canonical.com>]

On Mon, Mar 14, 2016 at 01:25:27PM -0400, Steven Rostedt wrote:
> On Mon, 14 Mar 2016 17:18:52 +0000
> Luis Henriques <luis.henriques@canonical.com> wrote:
> 
> > On Fri, Mar 11, 2016 at 11:04:00PM -0800, Greg Kroah-Hartman wrote:
> > > 
> > > This is a note to let you know that I've just added the patch titled
> > > 
> > >     tracing: Fix check for cpu online when event is disabled
> > > 
> > > to the 3.10-stable tree which can be found at:
> > >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > > 
> > > The filename of the patch is:
> > >      tracing-fix-check-for-cpu-online-when-event-is-disabled.patch
> > > and it can be found in the queue-3.10 subdirectory.
> > > 
> > > If you, or anyone else, feels it should not be added to the stable tree,
> > > please let <stable@vger.kernel.org> know about it.
> > >  
> > 
> > Please note that this patch was tagged for stable 3.18+.
> > 
> 
> Correct. That's because:
> 
> > > 
> > > Commit f37755490fe9b ("tracepoints: Do not trace when cpu is offline") added
> > > a check to make sure that tracepoints only get called when the cpu is
> > > online, as it uses rcu_read_lock_sched() for protection.
> 
> This was added much earlier and fixes a real bug in various places.
> 
> > > 
> > > Commit 3a630178fd5f3 ("tracing: generate RCU warnings even when tracepoints
> > > are disabled") added lockdep checks (including rcu checks) for events that
> > > are not enabled to catch possible RCU issues that would only be triggered if
> > > a trace event was enabled. Commit f37755490fe9b only stopped the warnings
> > > when the trace event was enabled but did not prevent warnings if the trace
> > > event was called when disabled.
> 
> The above wasn't added till 3.18, which warns when the trace event is
> not enabled. With the backported patch, it now triggers false warnings.
> But the false warnings wont exist before 3.18.
> 
> It doesn't hurt to backport this patch further, it's just not
> necessary, unless 3a630178fd5f3 was backported too. Was it?
> 
> -- Steve
> 

Thanks for clarifying, Steve.  I don't think commit 3a630178fd5f3 has
been backport to stable kernels, so if you're saying it doesn't hurt
to backport dc17147de328 I guess that's up to the stable maintainers
to include it or not.  Thanks!

Cheers,
--
Lu�s