From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
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,
walken@google.com, vincent.guittot@linaro.org,
laijs@cn.fujitsu.com
Cc: linux-arch@vger.kernel.org, nikunj@linux.vnet.ibm.com,
zhong@linux.vnet.ibm.com, linux-pm@vger.kernel.org,
fweisbec@gmail.com,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
linux-kernel@vger.kernel.org, rostedt@goodmis.org,
xiaoguangrong@linux.vnet.ibm.com, sbw@mit.edu,
Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
wangyun@linux.vnet.ibm.com,
"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
netdev@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
linuxppc-dev@lists.ozlabs.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH v2 02/45] CPU hotplug: Clarify the usage of different synchronization APIs
Date: Wed, 26 Jun 2013 01:56:01 +0530 [thread overview]
Message-ID: <20130625202601.16593.54501.stgit@srivatsabhat.in.ibm.com> (raw)
In-Reply-To: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com>
We have quite a few APIs now which help synchronize with CPU hotplug.
Among them, get/put_online_cpus() is the oldest and the most well-known,
so no problems there. By extension, its easy to comprehend the new
set : get/put_online_cpus_atomic().
But there is yet another set, which might appear tempting to use:
cpu_hotplug_disable()/cpu_hotplug_enable(). Add comments to clarify
that this latter set is NOT for general use and must be used only in
specific cases where the requirement is really to _disable_ hotplug
and not just to synchronize with it.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---
kernel/cpu.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 2d03398..860f51a 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -139,6 +139,13 @@ static void cpu_hotplug_done(void)
* the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
* hotplug path before performing hotplug operations. So acquiring that lock
* guarantees mutual exclusion from any currently running hotplug operations.
+ *
+ * Note: In most cases, this is *NOT* the function you need. If you simply
+ * want to avoid racing with CPU hotplug operations, use get/put_online_cpus()
+ * or get/put_online_cpus_atomic(), depending on the situation.
+ *
+ * This set of functions is reserved for cases where you really wish to
+ * _disable_ CPU hotplug and not just synchronize with it.
*/
void cpu_hotplug_disable(void)
{
next prev parent reply other threads:[~2013-06-25 20:29 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-25 20:25 [PATCH v2 00/45] CPU hotplug: stop_machine()-free CPU hotplug, part 1 Srivatsa S. Bhat
2013-06-25 20:25 ` [PATCH v2 01/45] CPU hotplug: Provide APIs to prevent CPU offline from atomic context Srivatsa S. Bhat
2013-06-25 20:26 ` Srivatsa S. Bhat [this message]
2013-06-25 20:26 ` [PATCH v2 03/45] Documentation, CPU hotplug: Recommend usage of get/put_online_cpus_atomic() Srivatsa S. Bhat
2013-06-25 20:26 ` [PATCH v2 04/45] CPU hotplug: Add infrastructure to check lacking hotplug synchronization Srivatsa S. Bhat
2013-06-25 20:26 ` [PATCH v2 05/45] CPU hotplug: Protect set_cpu_online() to avoid false-positives Srivatsa S. Bhat
2013-06-25 20:26 ` [PATCH v2 06/45] CPU hotplug: Sprinkle debugging checks to catch locking bugs Srivatsa S. Bhat
2013-06-25 20:26 ` [PATCH v2 07/45] CPU hotplug: Expose the new debug config option Srivatsa S. Bhat
2013-06-25 20:26 ` [PATCH v2 08/45] CPU hotplug: Convert preprocessor macros to static inline functions Srivatsa S. Bhat
2013-06-25 20:27 ` [PATCH v2 09/45] smp: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-25 20:27 ` [PATCH v2 10/45] sched/core: " Srivatsa S. Bhat
2013-06-25 20:27 ` [PATCH v2 11/45] migration: Use raw_spin_lock/unlock since interrupts are already disabled Srivatsa S. Bhat
2013-06-25 20:27 ` [PATCH v2 12/45] sched/fair: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-25 20:27 ` [PATCH v2 13/45] timer: " Srivatsa S. Bhat
2013-06-25 20:27 ` [PATCH v2 14/45] sched/rt: " Srivatsa S. Bhat
2013-06-25 20:27 ` [PATCH v2 15/45] rcu: " Srivatsa S. Bhat
2013-06-25 22:00 ` Paul E. McKenney
2013-06-26 14:09 ` Srivatsa S. Bhat
2013-06-26 14:29 ` David Laight
2013-06-26 14:34 ` Paul E. McKenney
2013-06-26 14:51 ` Steven Rostedt
2013-06-26 15:21 ` Tejun Heo
2013-06-26 15:33 ` Steven Rostedt
2013-06-26 17:29 ` Tejun Heo
2013-06-26 18:28 ` Srivatsa S. Bhat
2013-06-26 21:34 ` Tejun Heo
2013-06-27 6:53 ` Srivatsa S. Bhat
2013-06-26 18:22 ` Srivatsa S. Bhat
2013-06-27 8:54 ` David Laight
2013-06-27 10:06 ` Srivatsa S. Bhat
2013-06-26 14:45 ` Paul E. McKenney
2013-06-26 18:18 ` Srivatsa S. Bhat
2013-06-26 14:33 ` Paul E. McKenney
2013-06-25 20:28 ` [PATCH v2 16/45] tick-broadcast: " Srivatsa S. Bhat
2013-06-25 20:28 ` [PATCH v2 17/45] time/clocksource: " Srivatsa S. Bhat
2013-06-25 20:28 ` [PATCH v2 18/45] softirq: " Srivatsa S. Bhat
2013-06-25 20:28 ` [PATCH v2 19/45] irq: " Srivatsa S. Bhat
2013-06-25 20:29 ` [PATCH v2 20/45] net: " Srivatsa S. Bhat
2013-06-25 20:29 ` [PATCH v2 21/45] block: " Srivatsa S. Bhat
2013-06-25 20:29 ` [PATCH v2 22/45] percpu_counter: " Srivatsa S. Bhat
2013-06-25 20:29 ` [PATCH v2 23/45] infiniband: ehca: " Srivatsa S. Bhat
2013-06-25 20:29 ` [PATCH v2 24/45] [SCSI] fcoe: " Srivatsa S. Bhat
2013-06-25 20:30 ` [PATCH v2 25/45] staging/octeon: " Srivatsa S. Bhat
2013-06-25 20:45 ` Greg Kroah-Hartman
2013-06-25 20:30 ` [PATCH v2 26/45] x86: " Srivatsa S. Bhat
2013-06-25 20:30 ` [PATCH v2 27/45] perf/x86: " Srivatsa S. Bhat
2013-06-25 20:30 ` [PATCH v2 28/45] KVM: " Srivatsa S. Bhat
2013-06-26 8:20 ` Paolo Bonzini
2013-06-25 20:30 ` [PATCH v2 29/45] kvm/vmx: " Srivatsa S. Bhat
2013-06-26 7:46 ` Paolo Bonzini
2013-06-26 8:06 ` Srivatsa S. Bhat
2013-06-26 8:23 ` Paolo Bonzini
2013-06-26 8:41 ` Srivatsa S. Bhat
2013-06-26 8:57 ` Paolo Bonzini
2013-06-25 20:30 ` [PATCH v2 30/45] x86/xen: " Srivatsa S. Bhat
2013-06-25 20:31 ` [PATCH v2 31/45] alpha/smp: " Srivatsa S. Bhat
2013-06-25 20:31 ` [PATCH v2 32/45] blackfin/smp: " Srivatsa S. Bhat
2013-06-25 20:31 ` [PATCH v2 33/45] cris/smp: " Srivatsa S. Bhat
2013-06-25 20:32 ` [PATCH v2 34/45] hexagon/smp: " Srivatsa S. Bhat
2013-06-25 20:32 ` [PATCH v2 35/45] ia64: irq, perfmon: " Srivatsa S. Bhat
2013-06-25 20:32 ` [PATCH v2 36/45] ia64: smp, tlb: " Srivatsa S. Bhat
2013-06-25 20:32 ` [PATCH v2 37/45] m32r: " Srivatsa S. Bhat
2013-06-25 20:32 ` [PATCH v2 38/45] MIPS: " Srivatsa S. Bhat
2013-06-26 13:39 ` Ralf Baechle
2013-06-27 7:08 ` Srivatsa S. Bhat
2013-06-25 20:33 ` [PATCH v2 39/45] mn10300: " Srivatsa S. Bhat
2013-06-25 20:33 ` [PATCH v2 40/45] powerpc, irq: Use GFP_ATOMIC allocations in atomic context Srivatsa S. Bhat
2013-06-25 20:33 ` [PATCH v2 41/45] powerpc: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-25 20:33 ` [PATCH v2 42/45] powerpc: Use get/put_online_cpus_atomic() to avoid false-positive warning Srivatsa S. Bhat
2013-06-25 20:33 ` [PATCH v2 43/45] sh: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-25 20:33 ` [PATCH v2 44/45] sparc: " Srivatsa S. Bhat
2013-06-25 20:34 ` [PATCH v2 45/45] tile: " Srivatsa S. Bhat
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