Re: FAILED: patch "[PATCH] srcu: Allow use of Classic SRCU from both process and" failed to apply to 4.9-stable tree

Paul E. McKenney
2017-06-12T20:15:06Z

On Mon, Jun 12, 2017 at 09:17:34PM +0200, Greg KH wrote:
> On Mon, Jun 12, 2017 at 09:31:51AM -0700, Paul E. McKenney wrote:
> > On Mon, Jun 12, 2017 at 02:17:59PM +0200, gregkh@linuxfoundation.org wrote:
> > >
> > > The patch below does not apply to the 4.9-stable tree.
> > > If someone wants it applied there, or to any other stable or longterm
> > > tree, then please email the backport, including the original git commit
> > > id to <stable@vger.kernel.org>.
> >
> > Indeed, this won't apply cleanly to 4.9 and earlier because of some
> > changes to the way SRCU works. And if you try to make the obvious
> > adjustments to make the patch apply, you will break SRCU.
>
> Oh good, I was wondering about that, I thought I had backported it
> properly, but then I figured I really don't know how rcu works in
> detail, so decided to just punt and reject it :)

If it makes you feel better, the reason I know that it breaks SRCU is
because I backported the patches early this morning before I was fully
awake. Fortunately, rcutorture protested vigorously, saying this about
a 30-minute run:

WARNING: Summary: Bugs: 3494 Call Traces: 3494

Paolo pointed out at least one of the additional patches that would have
to be backported along with this one. If people start seeing failures on
the older kernels, I will of course make sure that the backport happens.

Thanx, Paul