From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: [PATCH v5 45/45] Documentation/cpu-hotplug: Remove references to stop_machine() Date: Tue, 22 Jan 2013 13:15:48 +0530 Message-ID: <20130122074543.13822.44724.stgit@srivatsabhat.in.ibm.com> References: <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> Sender: linux-kernel-owner@vger.kernel.org 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 Cc: rostedt@goodmis.org, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, rjw@sisk.pl, sbw@mit.edu, fweisbec@gmail.com, linux@arm.linux.org.uk, nikunj@linux.vnet.ibm.com, srivatsa.bhat@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-arch.vger.kernel.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 --- 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, From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp08.au.ibm.com ([202.81.31.141]:50604 "EHLO e23smtp08.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754743Ab3AVHsC (ORCPT ); Tue, 22 Jan 2013 02:48:02 -0500 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 17:46:29 +1000 From: "Srivatsa S. Bhat" Subject: [PATCH v5 45/45] Documentation/cpu-hotplug: Remove references to stop_machine() 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> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: 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 Cc: rostedt@goodmis.org, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, rjw@sisk.pl, sbw@mit.edu, fweisbec@gmail.com, linux@arm.linux.org.uk, nikunj@linux.vnet.ibm.com, srivatsa.bhat@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <20130122074548.Nnb1owosbdabhQYvl52XNQjo4DdZKG3k0ZLd1VgjFic@z> 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 --- 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,