linux-kernel - Re: [PATCH RFC] doc: rcu: remove obsolete (non-)requirement about disabling preemption

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Message-ID: <20181018211245.10baf496@vmware.local.home>
Date:   Thu, 18 Oct 2018 21:12:45 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Nikolay Borisov <nborisov@...e.com>,
        linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-doc@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH RFC] doc: rcu: remove obsolete (non-)requirement about
 disabling preemption

On Thu, 18 Oct 2018 17:19:32 -0700
"Paul E. McKenney" <paulmck@...ux.ibm.com> wrote:

> I figured that whoever calls preempt_enable_no_resched() is taking the
> responsibility for permitting preemption in the near future, and if they
> fail to do so, they will get called on it.  Hard to hide from the latency
> tracer, after all.  ;-)

Correct, and doing a search of preempt_enable_no_resched() I see
there's one in the ftrace ring buffer code, that was added a long time
ago (2008) to fix a recursion bug that no longer exists, and this now
can leak a preemption point.

I'll have to go fix that :-(

-- Steve