From nobody Mon Oct 6 08:05:27 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5CAB71F5827 for ; Wed, 23 Jul 2025 15:36:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753284963; cv=none; b=O5lsKgji+RmqwRNcU0KTkI/AfkuHgyEKOyXV56FSySxrOBM23jhHfY69WxkLydRitUB+QYSTnDkwCLBTdouR8ZoKqcDbzjDGazI7ChPvIWG8QlBTmyIJS6e+f0WRpJPpChTXY5t3Kg1RScGUgodZrb9hsEBJnLS7ZvJw61sNaqk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753284963; c=relaxed/simple; bh=MyJ++kcHYsc3TCfHXbv+NA4FXvwX5QEPx0gAXoTb3hY=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=PjVvOwZVXuODVrhME2XPAvkAlaM8PMiUSDbaF3e9kP3ORcTghrDY4mTKMaUgpBoPmDvpx/n7Kxzdd68JgXfoLXOwZdyL9ohGLtVV10M+pwNJzXumwsuWDMjC9EMOTTX5MDsT39pgVTxoe5PCnRTj8fCge+eNXV8KyAAzhGkCtD8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=H/z1oUoq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="H/z1oUoq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8BB6C4CEF1; Wed, 23 Jul 2025 15:36:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753284962; bh=MyJ++kcHYsc3TCfHXbv+NA4FXvwX5QEPx0gAXoTb3hY=; h=Date:From:To:Cc:Subject:References:From; b=H/z1oUoqdE4mhVOrC6MhD8WXLFY2KK+JNvR4Umc7VhVsk6sFHUJq9as9Gs2rAW9gw tmek4m+csrLGTiT/JQcu4X5Z74tzHSpMYIKrljVXszOAsaxzryjoP5How8/kBRSF3x hHBVf5N7Bt8AlkPnk6/yAs9Ha4we6KSn6qD7jPXJdJHPyEsS7dgOqsFMWg0KfUYdDi xfv86byfUFsTyTxjKVsbWy36q9xcHHP5pG+p+w0Nl/nID+STNUj1aFRtMKV4XnfSFW 3B0pb+ocdjM/r+zsh2zsnSIn7grPJfCnNNcUaE4gKLMUcBhxvJefm3U7K+Ln/PAqTI /JJSsrSqdV/4Q== Received: from rostedt by gandalf with local (Exim 4.98.2) (envelope-from ) id 1ueame-00000000LRE-1LUB; Wed, 23 Jul 2025 10:49:28 -0400 Message-ID: <20250723144928.172299624@kernel.org> User-Agent: quilt/0.68 Date: Wed, 23 Jul 2025 10:49:12 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Gabriele Monaco , Nam Cao Subject: [for-next][PATCH 5/8] tracing: Remove pointless memory barriers References: <20250723144907.219256132@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Nam Cao Memory barriers are useful to ensure memory accesses from one CPU appear in the original order as seen by other CPUs. Some smp_rmb() and smp_wmb() are used, but they are not ordering multiple memory accesses. Remove them. Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Gabriele Monaco Link: https://lore.kernel.org/20250626151940.1756398-1-namcao@linutronix.de Signed-off-by: Nam Cao Signed-off-by: Steven Rostedt (Google) --- kernel/trace/rv/rv.c | 6 ------ kernel/trace/trace.c | 7 ------- 2 files changed, 13 deletions(-) diff --git a/kernel/trace/rv/rv.c b/kernel/trace/rv/rv.c index e4077500a91d..c04a49da4328 100644 --- a/kernel/trace/rv/rv.c +++ b/kernel/trace/rv/rv.c @@ -675,8 +675,6 @@ static bool __read_mostly monitoring_on; */ bool rv_monitoring_on(void) { - /* Ensures that concurrent monitors read consistent monitoring_on */ - smp_rmb(); return READ_ONCE(monitoring_on); } =20 @@ -696,8 +694,6 @@ static ssize_t monitoring_on_read_data(struct file *fil= p, char __user *user_buf, static void turn_monitoring_off(void) { WRITE_ONCE(monitoring_on, false); - /* Ensures that concurrent monitors read consistent monitoring_on */ - smp_wmb(); } =20 static void reset_all_monitors(void) @@ -713,8 +709,6 @@ static void reset_all_monitors(void) static void turn_monitoring_on(void) { WRITE_ONCE(monitoring_on, true); - /* Ensures that concurrent monitors read consistent monitoring_on */ - smp_wmb(); } =20 static void turn_monitoring_on_with_reset(void) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 95ae7c4e5835..0dff4298fc0e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -936,7 +936,6 @@ int tracing_is_enabled(void) * return the mirror variable of the state of the ring buffer. * It's a little racy, but we don't really care. */ - smp_rmb(); return !global_trace.buffer_disabled; } =20 @@ -1107,8 +1106,6 @@ void tracer_tracing_on(struct trace_array *tr) * important to be fast than accurate. */ tr->buffer_disabled =3D 0; - /* Make the flag seen by readers */ - smp_wmb(); } =20 /** @@ -1640,8 +1637,6 @@ void tracer_tracing_off(struct trace_array *tr) * important to be fast than accurate. */ tr->buffer_disabled =3D 1; - /* Make the flag seen by readers */ - smp_wmb(); } =20 /** @@ -2710,8 +2705,6 @@ void trace_buffered_event_enable(void) =20 static void enable_trace_buffered_event(void *data) { - /* Probably not needed, but do it anyway */ - smp_rmb(); this_cpu_dec(trace_buffered_event_cnt); } =20 --=20 2.47.2