From: Joel Fernandes <joel@joelfernandes.org>
To: Scott Wood <swood@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
"Paul E . McKenney" <paulmck@linux.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Clark Williams <williams@redhat.com>
Subject: Re: [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep
Date: Fri, 23 Aug 2019 23:10:14 -0400 [thread overview]
Message-ID: <20190824031014.GB2731@google.com> (raw)
In-Reply-To: <433936e4c720e6b81f9b297fefaa592fd8a961ad.camel@redhat.com>
On Fri, Aug 23, 2019 at 02:28:46PM -0500, Scott Wood wrote:
> On Fri, 2019-08-23 at 18:20 +0200, Sebastian Andrzej Siewior wrote:
> > On 2019-08-21 18:19:05 [-0500], Scott Wood wrote:
> > > Without this, rcu_note_context_switch() will complain if an RCU read
> > > lock is held when migrate_enable() calls stop_one_cpu().
> > >
> > > Signed-off-by: Scott Wood <swood@redhat.com>
> > > ---
> > > v2: Added comment.
> > >
> > > If my migrate disable changes aren't taken, then pin_current_cpu()
> > > will also need to use sleeping_lock_inc() because calling
> > > __read_rt_lock() bypasses the usual place it's done.
> > >
> > > include/linux/sched.h | 4 ++--
> > > kernel/rcu/tree_plugin.h | 2 +-
> > > kernel/sched/core.c | 8 ++++++++
> > > 3 files changed, 11 insertions(+), 3 deletions(-)
> > >
> > > --- a/kernel/sched/core.c
> > > +++ b/kernel/sched/core.c
> > > @@ -7405,7 +7405,15 @@ void migrate_enable(void)
> > > unpin_current_cpu();
> > > preempt_lazy_enable();
> > > preempt_enable();
> > > +
> > > + /*
> > > + * sleeping_lock_inc suppresses a debug check for
> > > + * sleeping inside an RCU read side critical section
> > > + */
> > > + sleeping_lock_inc();
> > > stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
> > > + sleeping_lock_dec();
> >
> > this looks like an ugly hack. This sleeping_lock_inc() is used where we
> > actually hold a sleeping lock and schedule() which is okay. But this
> > would mean we hold a RCU lock and schedule() anyway. Is that okay?
>
> Perhaps the name should be changed, but the concept is the same -- RT-
> specific sleeping which should be considered involuntary for the purpose of
> debug checks. Voluntary sleeping is not allowed in an RCU critical section
> because it will break the critical section on certain flavors of RCU, but
> that doesn't apply to the flavor used on RT. Sleeping for a long time in an
> RCU critical section would also be a bad thing, but that also doesn't apply
> here.
I think the name should definitely be changed. At best, it is super confusing to
call it "sleeping_lock" for this scenario. In fact here, you are not even
blocking on a lock.
Maybe "sleeping_allowed" or some such.
thanks,
- Joel
next prev parent reply other threads:[~2019-08-24 3:10 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 23:19 [PATCH RT v2 0/3] RCU fixes Scott Wood
2019-08-21 23:19 ` [PATCH RT v2 1/3] rcu: Acquire RCU lock when disabling BHs Scott Wood
2019-08-21 23:33 ` Paul E. McKenney
2019-08-22 13:39 ` Joel Fernandes
2019-08-22 15:27 ` Paul E. McKenney
2019-08-23 1:50 ` Joel Fernandes
2019-08-23 2:11 ` Paul E. McKenney
2019-08-23 3:23 ` Scott Wood
2019-08-23 12:30 ` Paul E. McKenney
2019-08-23 16:17 ` Sebastian Andrzej Siewior
2019-08-23 19:46 ` Scott Wood
2019-08-26 15:59 ` Sebastian Andrzej Siewior
2019-08-26 23:21 ` Scott Wood
2019-08-23 2:36 ` Scott Wood
2019-08-23 2:54 ` Paul E. McKenney
2019-08-21 23:19 ` [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep Scott Wood
2019-08-21 23:35 ` Paul E. McKenney
2019-08-23 1:21 ` Scott Wood
2019-08-23 16:20 ` Sebastian Andrzej Siewior
2019-08-23 19:28 ` Scott Wood
2019-08-24 3:10 ` Joel Fernandes [this message]
2019-08-26 15:25 ` Sebastian Andrzej Siewior
2019-08-26 16:29 ` Paul E. McKenney
2019-08-26 17:49 ` Scott Wood
2019-08-26 18:12 ` Paul E. McKenney
2019-08-27 9:23 ` Sebastian Andrzej Siewior
2019-08-27 13:08 ` Joel Fernandes
2019-08-27 15:58 ` Paul E. McKenney
2019-08-27 16:06 ` Joel Fernandes
2019-08-27 15:53 ` Paul E. McKenney
2019-08-28 9:27 ` Sebastian Andrzej Siewior
2019-08-28 12:54 ` Paul E. McKenney
2019-08-28 13:14 ` Sebastian Andrzej Siewior
2019-08-28 13:59 ` Joel Fernandes
2019-08-28 15:51 ` Paul E. McKenney
2019-08-28 15:50 ` Paul E. McKenney
2019-08-21 23:19 ` [PATCH RT v2 3/3] rcu: Disable use_softirq on PREEMPT_RT Scott Wood
2019-08-21 23:40 ` Paul E. McKenney
2019-08-23 16:32 ` Sebastian Andrzej Siewior
2019-08-22 13:59 ` Joel Fernandes
2019-08-22 15:29 ` Paul E. McKenney
2019-08-22 19:31 ` Scott Wood
2019-08-23 0:52 ` Joel Fernandes
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