From patchwork Tue Jan 22 07:45:48 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Srivatsa S. Bhat" X-Patchwork-Id: 2017021 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) by patchwork2.kernel.org (Postfix) with ESMTP id B747EDF2EB for ; Tue, 22 Jan 2013 08:00:11 +0000 (UTC) Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1TxYjS-0003RV-UT; Tue, 22 Jan 2013 07:57:23 +0000 Received: from e23smtp08.au.ibm.com ([202.81.31.141]) by merlin.infradead.org with esmtps (Exim 4.76 #1 (Red Hat Linux)) id 1TxYaP-0001zN-Jl for linux-arm-kernel@lists.infradead.org; Tue, 22 Jan 2013 07:48:02 +0000 Received: from /spool/local by e23smtp08.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 22 Jan 2013 17:46:26 +1000 Received: from d23dlp01.au.ibm.com (202.81.31.203) by e23smtp08.au.ibm.com (202.81.31.205) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Tue, 22 Jan 2013 17:46:24 +1000 Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [9.190.235.152]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id AE69F2CE804A for ; Tue, 22 Jan 2013 18:47:55 +1100 (EST) Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.234.96]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r0M7a1jQ64159784 for ; Tue, 22 Jan 2013 18:36:01 +1100 Received: from d23av01.au.ibm.com (loopback [127.0.0.1]) by d23av01.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r0M7lrQk010175 for ; Tue, 22 Jan 2013 18:47:54 +1100 Received: from srivatsabhat.in.ibm.com (srivatsabhat.in.ibm.com [9.124.35.112]) by d23av01.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id r0M7lX53009755; Tue, 22 Jan 2013 18:47:35 +1100 From: "Srivatsa S. Bhat" Subject: [PATCH v5 45/45] Documentation/cpu-hotplug: Remove references to stop_machine() To: tglx@linutronix.de, peterz@infradead.org, tj@kernel.org, oleg@redhat.com, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org Date: Tue, 22 Jan 2013 13:15:48 +0530 Message-ID: <20130122074543.13822.44724.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> References: <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13012207-5140-0000-0000-000002A8FC54 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20130122_024802_116047_09731591 X-CRM114-Status: GOOD ( 14.75 ) X-Spam-Score: -4.6 (----) X-Spam-Report: SpamAssassin version 3.3.2 on merlin.infradead.org summary: Content analysis details: (-4.6 points) pts rule name description ---- ---------------------- -------------------------------------------------- -5.0 RCVD_IN_DNSWL_HI RBL: Sender listed at http://www.dnswl.org/, high trust [202.81.31.141 listed in list.dnswl.org] 3.0 KHOP_BIG_TO_CC Sent to 10+ recipients instaed of Bcc or a list -0.7 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Cc: linux-arch@vger.kernel.org, linux@arm.linux.org.uk, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, fweisbec@gmail.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, xiaoguangrong@linux.vnet.ibm.com, rjw@sisk.pl, sbw@mit.edu, wangyun@linux.vnet.ibm.com, srivatsa.bhat@linux.vnet.ibm.com, netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org Since stop_machine() is no longer used in the CPU offline path, we cannot disable CPU hotplug using preempt_disable()/local_irq_disable() etc. We need to use the newly introduced get/put_online_cpus_atomic() APIs. Reflect this in the documentation. Cc: Rob Landley Cc: linux-doc@vger.kernel.org Signed-off-by: Srivatsa S. Bhat Reviewed-by: Paul E. McKenney --- Documentation/cpu-hotplug.txt | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt index 9f40135..7f907ec 100644 --- a/Documentation/cpu-hotplug.txt +++ b/Documentation/cpu-hotplug.txt @@ -113,13 +113,15 @@ Never use anything other than cpumask_t to represent bitmap of CPUs. #include get_online_cpus() and put_online_cpus(): -The above calls are used to inhibit cpu hotplug operations. While the +The above calls are used to inhibit cpu hotplug operations, when invoked from +non-atomic context (because the above functions can sleep). While the cpu_hotplug.refcount is non zero, the cpu_online_mask will not change. -If you merely need to avoid cpus going away, you could also use -preempt_disable() and preempt_enable() for those sections. -Just remember the critical section cannot call any -function that can sleep or schedule this process away. The preempt_disable() -will work as long as stop_machine_run() is used to take a cpu down. + +However, if you are executing in atomic context (ie., you can't afford to +sleep), and you merely need to avoid cpus going offline, you can use +get_online_cpus_atomic() and put_online_cpus_atomic() for those sections. +Just remember the critical section cannot call any function that can sleep or +schedule this process away. CPU Hotplug - Frequently Asked Questions. @@ -360,6 +362,9 @@ A: There are two ways. If your code can be run in interrupt context, use return err; } + If my_func_on_cpu() itself cannot block, use get/put_online_cpus_atomic() + instead of get/put_online_cpus() to prevent CPUs from going offline. + Q: How do we determine how many CPUs are available for hotplug. A: There is no clear spec defined way from ACPI that can give us that information today. Based on some input from Natalie of Unisys,