From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Mark Rutland <mark.rutland@arm.com>,
David Howells <dhowells@redhat.com>,
linux-arch <linux-arch@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH RFC tip/core/rcu 11/15] tracepoint: Remove smp_read_barrier_depends() from comment
Date: Tue, 10 Oct 2017 01:12:38 +0000 (UTC) [thread overview]
Message-ID: <506678791.34748.1507597958832.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20171009203116.4246818c@gandalf.local.home>
----- On Oct 9, 2017, at 8:31 PM, rostedt rostedt@goodmis.org wrote:
> [ added Mathieu ]
>
> On Mon, 9 Oct 2017 17:22:45 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
>> The comment in tracepoint_add_func() mentions smp_read_barrier_depends(),
>> whose use should be quite restricted. This commit updates the comment
>> to instead mention the smp_store_release() and rcu_dereference_sched()
>> that the current code actually uses.
>>
>> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>> Cc: Ingo Molnar <mingo@kernel.org>
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>
> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
>
Yeah I think we don't need to spell out the implementation of
rcu_dereference_sched() there (which actually uses lockless_dereference(),
which indeed ends up relying on smp_read_barrier_depends()). The comment
was a bit too low-level for the benefit of its audience.
I agree with the change.
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Thanks,
Mathieu
> -- Steve
>
>> ---
>> kernel/tracepoint.c | 9 ++++-----
>> 1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
>> index 685c50ae6300..671b13457387 100644
>> --- a/kernel/tracepoint.c
>> +++ b/kernel/tracepoint.c
>> @@ -212,11 +212,10 @@ static int tracepoint_add_func(struct tracepoint *tp,
>> }
>>
>> /*
>> - * rcu_assign_pointer has a smp_wmb() which makes sure that the new
>> - * probe callbacks array is consistent before setting a pointer to it.
>> - * This array is referenced by __DO_TRACE from
>> - * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
>> - * is used.
>> + * rcu_assign_pointer has as smp_store_release() which makes sure
>> + * that the new probe callbacks array is consistent before setting
>> + * a pointer to it. This array is referenced by __DO_TRACE from
>> + * include/linux/tracepoint.h using rcu_dereference_sched().
>> */
>> rcu_assign_pointer(tp->funcs, tp_funcs);
> > if (!static_key_enabled(&tp->key))
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2017-10-10 1:10 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-10 0:19 [PATCH RFC tip/core/rcu 0/15] Remove to-be-unneeded smp_read_barrier_depends() Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 01/15] doc: READ_ONCE() now implies smp_barrier_depends() Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 02/15] mn10300: READ_ONCE() now implies smp_read_barrier_depends() Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 03/15] drivers/net/ethernet/qlogic/qed: Fix __qed_spq_block() ordering Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 04/15] fs/dcache: Use release-acquire for name/length update Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 05/15] percpu: READ_ONCE() now implies smp_read_barrier_depends() Paul E. McKenney
2017-10-10 14:08 ` Tejun Heo
2017-10-10 15:30 ` Paul E. McKenney
2017-10-10 15:49 ` Tejun Heo
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 06/15] rcu: Adjust read-side accessor comments for READ_ONCE() Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 07/15] rtnetlink: Update now-misleading smp_read_barrier_depends() comment Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 08/15] seqlock: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 09/15] uprobes: " Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 10/15] locking: Remove smp_read_barrier_depends() from queued_spin_lock_slowpath() Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 11/15] tracepoint: Remove smp_read_barrier_depends() from comment Paul E. McKenney
2017-10-10 0:31 ` Steven Rostedt
2017-10-10 1:12 ` Mathieu Desnoyers [this message]
2017-10-10 15:32 ` Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends() Paul E. McKenney
2017-10-10 8:39 ` Peter Zijlstra
2017-10-10 9:36 ` David Howells
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 13/15] mm/ksm: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 14/15] netfilter: " Paul E. McKenney
2017-10-10 8:43 ` Peter Zijlstra
2017-10-10 15:56 ` Paul E. McKenney
2017-10-10 0:22 ` [PATCH RFC tip/core/rcu 15/15] keyring: " Paul E. McKenney
2017-10-10 9:35 ` [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends() David Howells
2017-10-10 15:50 ` Paul E. McKenney
2017-10-10 15:54 ` Peter Zijlstra
2017-10-10 16:05 ` Paul E. McKenney
2017-10-11 12:19 ` David Howells
2017-10-11 12:22 ` Will Deacon
2017-10-11 12:54 ` Paul E. McKenney
2017-10-11 14:18 ` Will Deacon
2017-10-11 14:50 ` Paul E. McKenney
2017-10-11 12:58 ` Paul E. McKenney
2017-10-11 15:17 ` David Howells
2017-10-11 15:59 ` Paul E. McKenney
2017-10-11 16:12 ` Peter Zijlstra
2017-10-11 16:24 ` Peter Zijlstra
2017-10-11 16:47 ` Paul E. McKenney
2017-10-11 16:54 ` Peter Zijlstra
2017-10-11 17:06 ` Paul E. McKenney
2017-10-11 17:11 ` Peter Zijlstra
2017-10-11 17:34 ` Paul E. McKenney
2017-10-11 18:43 ` Dmitry Vyukov
2017-10-11 18:56 ` Linus Torvalds
2017-10-11 19:28 ` Paul E. McKenney
2017-10-11 19:59 ` Dmitry Vyukov
2017-10-11 17:14 ` Paul E. McKenney
2017-10-11 17:19 ` Mark Rutland
2017-10-11 16:50 ` Paul E. McKenney
2017-10-11 16:07 ` David Howells
2017-10-11 16:17 ` Peter Zijlstra
2017-10-11 16:19 ` Paul E. McKenney
2017-10-11 15:28 ` David Howells
2017-10-11 16:02 ` Paul E. McKenney
2017-10-10 9:59 ` David Howells
2017-10-10 15:52 ` Paul E. McKenney
2017-10-11 12:21 ` [PATCH RFC tip/core/rcu 0/15] Remove to-be-unneeded smp_read_barrier_depends() David Howells
2017-10-11 12:56 ` Paul E. McKenney
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