From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Byungchul Park <byungchul.park@lge.com>,
Scott Wood <swood@redhat.com>,
Joel Fernandes <joel@joelfernandes.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
rcu <rcu@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Josh Triplett <josh@joshtriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs
Date: Sat, 29 Jun 2019 21:35:48 +0200 [thread overview]
Message-ID: <20190629193548.GA8308@andrea> (raw)
In-Reply-To: <20190629191515.GM26519@linux.ibm.com>
On Sat, Jun 29, 2019 at 12:15:15PM -0700, Paul E. McKenney wrote:
> On Sat, Jun 29, 2019 at 08:09:10PM +0200, Andrea Parri wrote:
> > On Sat, Jun 29, 2019 at 09:55:33AM -0700, Paul E. McKenney wrote:
> > > On Sat, Jun 29, 2019 at 05:12:36PM +0200, Andrea Parri wrote:
> > > > Hi Steve,
> > > >
> > > > > As Paul stated, interrupts are synchronization points. Archs can only
> > > > > play games with ordering when dealing with entities outside the CPU
> > > > > (devices and other CPUs). But if you have assembly that has two stores,
> > > > > and an interrupt comes in, the arch must guarantee that the stores are
> > > > > done in that order as the interrupt sees it.
> > > >
> > > > Hopefully I'm not derailing the conversation too much with my questions
> > > > ... but I was wondering if we had any documentation (or inline comments)
> > > > elaborating on this "interrupts are synchronization points"?
> > >
> > > I don't know of any, but I would suggest instead looking at something
> > > like the Hennessey and Patterson computer-architecture textbook.
> > >
> > > Please keep in mind that the rather detailed documentation on RCU is a
> > > bit of an outlier due to the fact that there are not so many textbooks
> > > that cover RCU. If we tried to replicate all of the relevant textbooks
> > > in the Documentation directory, it would be quite a large mess. ;-)
> >
> > You know some developers considered it worth to develop formal specs in
> > order to better understand concepts such as "synchronization" and "IRQs
> > (processing)"! ... ;-) I still think that adding a few paragraphs (if
> > only in informal prose) to explain that "interrupts are synchronization
> > points" wouln't hurt. And you're right, I guess we may well start from
> > a reference to H&P...
> >
> > Remark: we do have code which (while acknowledging that "interrupts are
> > synchronization points") doesn't quite seem to "believe it", c.f., e.g.,
> > kernel/sched/membarrier.c:ipi_mb(). So, I guess the follow-up question
> > would be "Would we better be (more) paranoid? ..."
>
> As Steve said that I said, they are synchronization points from the
> viewpoint of code within the interrupted CPU. Unless the architecture
> code does as smp_mb() on interrupt entry and exit (which perhaps some
> do, for all I know, maybe all of them do by now), memory accesses could
> still be reordered across the interrupt from the perspective of other
> CPUs and devices on the system.
Yes, I got it. See:
https://lkml.kernel.org/r/20190629182132.GA5666@andrea
Still...
Andrea
next prev parent reply other threads:[~2019-06-29 19:35 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-26 13:54 [RFC] Deadlock via recursive wakeup via RCU with threadirqs Sebastian Andrzej Siewior
2019-06-26 16:25 ` Paul E. McKenney
2019-06-27 7:47 ` Sebastian Andrzej Siewior
2019-06-27 15:52 ` Paul E. McKenney
2019-06-27 14:24 ` Joel Fernandes
2019-06-27 14:34 ` Steven Rostedt
2019-06-27 15:30 ` Joel Fernandes
2019-06-27 15:37 ` Joel Fernandes
2019-06-27 15:40 ` Sebastian Andrzej Siewior
2019-06-27 15:42 ` Joel Fernandes
2019-06-27 17:43 ` Joel Fernandes
2019-06-27 17:46 ` Joel Fernandes
2019-06-27 18:11 ` Paul E. McKenney
2019-06-27 18:27 ` Joel Fernandes
2019-06-27 18:51 ` Joel Fernandes
2019-06-27 19:14 ` Paul E. McKenney
2019-06-27 19:15 ` Paul E. McKenney
2019-06-27 18:30 ` Paul E. McKenney
2019-06-27 20:45 ` Paul E. McKenney
2019-06-27 15:55 ` Paul E. McKenney
2019-06-27 16:47 ` Joel Fernandes
2019-06-27 17:38 ` Paul E. McKenney
2019-06-27 18:16 ` Joel Fernandes
2019-06-27 18:41 ` Paul E. McKenney
2019-06-27 20:17 ` Scott Wood
2019-06-27 20:36 ` Paul E. McKenney
2019-06-28 7:31 ` Byungchul Park
2019-06-28 7:43 ` Byungchul Park
2019-06-28 8:14 ` Byungchul Park
2019-06-28 8:24 ` Byungchul Park
2019-06-28 12:24 ` Paul E. McKenney
2019-06-28 9:10 ` Byungchul Park
2019-06-28 9:28 ` Byungchul Park
2019-06-28 12:21 ` Paul E. McKenney
2019-06-28 10:40 ` Byungchul Park
2019-06-28 12:27 ` Paul E. McKenney
2019-06-28 15:44 ` Steven Rostedt
2019-06-29 15:12 ` Andrea Parri
2019-06-29 16:55 ` Paul E. McKenney
2019-06-29 18:09 ` Andrea Parri
2019-06-29 18:21 ` Andrea Parri
2019-06-29 19:15 ` Paul E. McKenney
2019-06-29 19:35 ` Andrea Parri [this message]
2019-06-30 23:55 ` Byungchul Park
2019-06-28 14:15 ` Peter Zijlstra
2019-06-28 15:54 ` Paul E. McKenney
2019-06-28 16:04 ` Peter Zijlstra
2019-06-28 17:20 ` Paul E. McKenney
2019-07-01 9:42 ` Peter Zijlstra
2019-07-01 10:24 ` Sebastian Andrzej Siewior
2019-07-01 12:23 ` Paul E. McKenney
2019-07-01 14:00 ` Peter Zijlstra
2019-07-01 16:01 ` Paul E. McKenney
2019-06-28 20:01 ` Scott Wood
2019-07-01 9:45 ` Peter Zijlstra
2019-06-28 13:54 ` Peter Zijlstra
2019-06-28 15:30 ` Paul E. McKenney
2019-06-28 18:40 ` Sebastian Andrzej Siewior
2019-06-28 18:52 ` Paul E. McKenney
2019-06-28 19:24 ` Joel Fernandes
2019-06-28 20:04 ` Paul E. McKenney
2019-06-28 21:40 ` Joel Fernandes
2019-06-28 22:25 ` Paul E. McKenney
2019-06-28 23:12 ` Joel Fernandes
2019-06-29 0:06 ` Paul E. McKenney
2019-06-28 16:40 ` Joel Fernandes
2019-06-28 16:45 ` Joel Fernandes
2019-06-28 17:30 ` Paul E. McKenney
2019-06-28 17:41 ` Paul E. McKenney
2019-06-28 17:45 ` Sebastian Andrzej Siewior
2019-06-28 18:07 ` Joel Fernandes
2019-06-28 18:20 ` Sebastian Andrzej Siewior
2019-07-01 2:08 ` Joel Fernandes
2019-06-28 18:22 ` Paul E. McKenney
2019-06-28 19:29 ` Joel Fernandes
2019-06-28 20:06 ` Paul E. McKenney
2019-06-28 18:05 ` Joel Fernandes
2019-06-28 18:23 ` Paul E. McKenney
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