On Wed, 5 Nov 2014, Steven Rostedt wrote: > On Wed, 5 Nov 2014 14:50:41 +0100 > Juerg Haefliger <juergh@xxxxxxxxx> wrote: > > > On Sun, Nov 2, 2014 at 8:30 AM, Mike Galbraith <umgwanakikbuti@xxxxxxxxx> > > wrote: > > > > > > On Fri, 2014-10-31 at 17:03 -0400, Steven Rostedt wrote: > > > > Dear RT Folks, > > > > > > > > I'm pleased to announce the 3.14.23-rt20 stable release. > > > > > > > > This is the first 3.14-rt release in the stable-rt series. Normally I > > > > wait till the next development release is out before I pull in a new > > > > one. That is, I would pull in 3.14-rt when 3.16-rt or later was > > > > released. But because development is now moving at a "hobbyist rate" > > > > (read http://lwn.net/Articles/617140/ for details) > > > > and 3.14-rt is no longer being developed against, I figured it was > > > time > > > > to put it under the "stable-rt" umbrella. > > > > > > I piddled about with it yesterday, found that you can't change cpufreq > > > governor IFF the tree is configured as rt, but works fine as voluntary > > > preempt. > > > > The problem seems to be this patch: https://lkml.org/lkml/2014/4/8/584 > > > > The cpufreq code does nested down_read_trylocks and only the first one > > succeeds: > > > > drivers/cpufreq/cpufreq.c: > > store > > down_read_trylock(cpufreq_rwsem) <- succeeds > > store_scaling_governor > > cpufreq_get_policy > > cpufreq_cpu_get > > down_read_trylock(cpufreq_rwsem) <-- fails > > > > Reverting the above patch 'fixes' the problem. I don't understand Steven's > > commit comment that readers of rwsem are not allowed to nest in mainline > > since this works just fine in mainline. > > When we allow multiple readers, this will be allowed. But even in > mainline, if a writer were to come in and block between those two > down_read_trylocks(), the second trylock would fail. > > PREEMPT_RT just has that fail all the time as we only allow an rwsem to > be held by a single reader. Errm. The reader holds the sem already. So that's a recursive read lock which should always succeed. And rt_read_trylock() has that implemented. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
