From: Peter Zijlstra <peterz@infradead.org>
To: Amol Grover <frextrite@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
linux-kernel@vger.kernel.org,
linux-kernel-mentees@lists.linuxfoundation.org,
Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH 2/2] events: callchain: Use RCU API to access RCU pointer
Date: Thu, 30 Jan 2020 14:32:48 +0100 [thread overview]
Message-ID: <20200130133248.GW14914@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200130101451.GA11015@workstation-portable>
On Thu, Jan 30, 2020 at 03:44:51PM +0530, Amol Grover wrote:
> > > > diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> > > > index f91e1f41d25d..a672d02a1b3a 100644
> > > > --- a/kernel/events/callchain.c
> > > > +++ b/kernel/events/callchain.c
> > > > @@ -62,7 +62,8 @@ static void release_callchain_buffers(void)
> > > > {
> > > > struct callchain_cpus_entries *entries;
> > > >
> > > > - entries = callchain_cpus_entries;
> > > > + entries = rcu_dereference_protected(callchain_cpus_entries,
> > > > + lockdep_is_held(&callchain_mutex));
> > >
> > >
> > > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> >
> > Do we really need that smp_read_barrier_depends() here? Then again, I
> > don't suppose this is a fast path.
> >
>
> rcu_dereference_protected is actually a lightweight API and IIRC it
> omits the READ_ONCE() and hence the memory barriers.
Oh argh, indeed. I suppose I should've had more tea this morning.
next prev parent reply other threads:[~2020-01-30 13:33 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 16:08 [PATCH 1/2] events: callchain: Annotate RCU pointer with __rcu Amol Grover
2020-01-29 16:08 ` [PATCH 2/2] events: callchain: Use RCU API to access RCU pointer Amol Grover
2020-01-29 22:19 ` Joel Fernandes
2020-01-30 8:23 ` Peter Zijlstra
2020-01-30 10:14 ` Amol Grover
2020-01-30 13:32 ` Peter Zijlstra [this message]
2020-01-29 22:19 ` [PATCH 1/2] events: callchain: Annotate RCU pointer with __rcu Joel Fernandes
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