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From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Joel Fernandes <joel@joelfernandes.org>,
	Byungchul Park <byungchul.park@lge.com>,
	jiangshanlai@gmail.com, josh@joshtriplett.org,
	mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org,
	kernel-team@lge.com, peterz@infradead.org
Subject: Re: [PATCH] rcu: Report a quiescent state when it's exactly in the state
Date: Sat, 12 May 2018 13:26:47 -0400	[thread overview]
Message-ID: <20180512132647.2923f7cf@gandalf.local.home> (raw)
In-Reply-To: <20180512144119.GJ26088@linux.vnet.ibm.com>

On Sat, 12 May 2018 07:41:19 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> Don't get me wrong, this discussion was quite useful to me.  We probably
> need to at least change the comments, and perhaps the code as well.  But
> I agree that we need input from Peter and Steven to make much more forward
> progress.

It's the weekend so I skimmed more than read this thread, but I will
just add this.

The table Joel posted is interesting, and perhaps we should keep things
consistent with that. But that said, with respect to task-RCU, as
nothing on a trampoline should ever call cond_resched() (and perhaps I
should add code in lockdep that verifies this), we just want a
quiescent state that tells us that the task has left the trampoline. A
cond_resched() should be one of those points that does.

It really has nothing to do with scheduling or preemption. The issue is
that if a task is on a trampoline and gets preempted, there's no
knowing when it is off that trampoline where we can free it. We need to
have places in the kernel that we know is a quiescent state to move
task-RCU forward. cond_resched() seems to be one of them. schedule
itself can not be, because it can be called from an interrupt preempting
a task while it is on the trampoline.

-- Steve

  reply	other threads:[~2018-05-12 17:26 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-11  8:30 Byungchul Park
2018-05-11 12:57 ` Byungchul Park
2018-05-11 16:17   ` Paul E. McKenney
2018-05-11 16:23     ` Steven Rostedt
2018-05-11 16:25       ` Steven Rostedt
2018-05-11 16:27         ` Steven Rostedt
2018-05-11 17:27           ` Paul E. McKenney
2018-05-11 17:29             ` Steven Rostedt
2018-05-11 22:41     ` Joel Fernandes
2018-05-12  5:08       ` Paul E. McKenney
2018-05-12  6:30         ` Joel Fernandes
2018-05-12 14:41           ` Paul E. McKenney
2018-05-12 17:26             ` Steven Rostedt [this message]
2018-05-14  3:11               ` Byungchul Park
2018-05-13  0:09             ` Joel Fernandes
2018-05-14  2:59       ` Byungchul Park
2018-05-14 14:25         ` Byungchul Park
2018-05-14 21:04         ` Paul E. McKenney
2018-05-15  0:18           ` Byungchul Park

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