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    SubjectRe: [tip:smp/hotplug] cpu/hotplug: Restructure FROZEN state handling
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    On 3/1/16 2:51 PM, tip-bot for Thomas Gleixner wrote:
    > Commit-ID: 090e77c391dd983c8945b8e2e16d09f378d2e334
    > Gitweb: http://git.kernel.org/tip/090e77c391dd983c8945b8e2e16d09f378d2e334
    > Author: Thomas Gleixner <tglx@linutronix.de>
    > AuthorDate: Fri, 26 Feb 2016 18:43:23 +0000
    > Committer: Thomas Gleixner <tglx@linutronix.de>
    > CommitDate: Tue, 1 Mar 2016 20:36:53 +0100
    >
    > cpu/hotplug: Restructure FROZEN state handling
    >
    > There are only a few callbacks which really care about FROZEN
    > vs. !FROZEN. No need to have extra states for this.
    >
    > Publish the frozen state in an extra variable which is updated under
    > the hotplug lock and let the users interested deal with it w/o
    > imposing that extra state checks on everyone.
    >
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    > Cc: linux-arch@vger.kernel.org
    > Cc: Rik van Riel <riel@redhat.com>
    > Cc: Rafael Wysocki <rafael.j.wysocki@intel.com>
    > Cc: "Srivatsa S. Bhat" <srivatsa@mit.edu>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Cc: Arjan van de Ven <arjan@linux.intel.com>
    > Cc: Sebastian Siewior <bigeasy@linutronix.de>
    > Cc: Rusty Russell <rusty@rustcorp.com.au>
    > Cc: Steven Rostedt <rostedt@goodmis.org>
    > Cc: Oleg Nesterov <oleg@redhat.com>
    > Cc: Tejun Heo <tj@kernel.org>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
    > Cc: Linus Torvalds <torvalds@linux-foundation.org>
    > Cc: Paul Turner <pjt@google.com>
    > Link: http://lkml.kernel.org/r/20160226182340.334912357@linutronix.de
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    > ---
    > include/linux/cpu.h | 2 ++
    > kernel/cpu.c | 69 ++++++++++++++++++++++-------------------------------
    > 2 files changed, 31 insertions(+), 40 deletions(-)
    >
    > diff --git a/include/linux/cpu.h b/include/linux/cpu.h
    > index d2ca8c3..f2fb549 100644
    > --- a/include/linux/cpu.h
    > +++ b/include/linux/cpu.h
    > @@ -118,6 +118,7 @@ enum {
    >
    >
    > #ifdef CONFIG_SMP
    > +extern bool cpuhp_tasks_frozen;
    > /* Need to know about CPUs going up/down? */
    > #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE)
    > #define cpu_notifier(fn, pri) { \
    > @@ -177,6 +178,7 @@ extern void cpu_maps_update_done(void);
    > #define cpu_notifier_register_done cpu_maps_update_done
    >
    > #else /* CONFIG_SMP */
    > +#define cpuhp_tasks_frozen 0
    >
    > #define cpu_notifier(fn, pri) do { (void)(fn); } while (0)
    > #define __cpu_notifier(fn, pri) do { (void)(fn); } while (0)
    > diff --git a/kernel/cpu.c b/kernel/cpu.c
    > index 5b9d396..41a6cb8 100644
    > --- a/kernel/cpu.c
    > +++ b/kernel/cpu.c
    > @@ -29,6 +29,8 @@
    > #ifdef CONFIG_SMP
    > /* Serializes the updates to cpu_online_mask, cpu_present_mask */
    > static DEFINE_MUTEX(cpu_add_remove_lock);
    > +bool cpuhp_tasks_frozen;
    > +EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);
    >

    One small nitpick though: we don't need to export this symbol yet; it can
    be deferred until the callbacks that need it are actually modified to use
    this value (presumably in a later patchset).

    Regards,
    Srivatsa S. Bhat

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