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    Subject[PATCH v9 4/8] smp: add func to IPI cpus based on parameter func
    Date
    Add the on_each_cpu_cond() function that wraps on_each_cpu_mask()
    and calculates the cpumask of cpus to IPI by calling a function supplied
    as a parameter in order to determine whether to IPI each specific cpu.

    The function works around allocation failure of cpumask variable in
    CONFIG_CPUMASK_OFFSTACK=y by itereating over cpus sending an IPI a
    time via smp_call_function_single().

    The function is useful since it allows to seperate the specific
    code that decided in each case whether to IPI a specific cpu for
    a specific request from the common boilerplate code of handling
    creating the mask, handling failures etc.

    Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Acked-by: Michal Nazarewicz <mina86@mina86.com>
    Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    CC: Chris Metcalf <cmetcalf@tilera.com>
    CC: Christoph Lameter <cl@linux-foundation.org>
    CC: Frederic Weisbecker <fweisbec@gmail.com>
    CC: Russell King <linux@arm.linux.org.uk>
    CC: linux-mm@kvack.org
    CC: Pekka Enberg <penberg@kernel.org>
    CC: Matt Mackall <mpm@selenic.com>
    CC: Sasha Levin <levinsasha928@gmail.com>
    CC: Rik van Riel <riel@redhat.com>
    CC: Andi Kleen <andi@firstfloor.org>
    CC: Alexander Viro <viro@zeniv.linux.org.uk>
    CC: linux-fsdevel@vger.kernel.org
    CC: Avi Kivity <avi@redhat.com>
    CC: Kosaki Motohiro <kosaki.motohiro@gmail.com>
    CC: Milton Miller <miltonm@bga.com>
    ---
    include/linux/smp.h | 25 ++++++++++++++++++++
    kernel/smp.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++
    2 files changed, 87 insertions(+), 0 deletions(-)

    diff --git a/include/linux/smp.h b/include/linux/smp.h
    index d0adb78..46e2267 100644
    --- a/include/linux/smp.h
    +++ b/include/linux/smp.h
    @@ -109,6 +109,15 @@ void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
    void *info, bool wait);

    /*
    + * Call a function on each processor for which the supplied function
    + * cond_func returns a positive value. This may include the local
    + * processor.
    + */
    +void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
    + smp_call_func_t func, void *info, bool wait,
    + gfp_t gfp_flags);
    +
    +/*
    * Mark the boot cpu "online" so that it can call console drivers in
    * printk() and can access its per-cpu storage.
    */
    @@ -153,6 +162,22 @@ static inline int up_smp_call_function(smp_call_func_t func, void *info)
    local_irq_enable(); \
    } \
    } while (0)
    +/*
    + * Preemption is disabled here to make sure the
    + * cond_func is called under the same condtions in UP
    + * and SMP.
    + */
    +#define on_each_cpu_cond(cond_func, func, info, wait, gfp_flags) \
    + do {
    + void *__info = (info); \
    + preempt_disable(); \
    + if ((cond_func)(0, __info)) { \
    + local_irq_disable(); \
    + (func)(__info); \
    + local_irq_enable(); \
    + } \
    + preempt_enable(); \
    + } while (0)

    static inline void smp_send_reschedule(int cpu) { }
    #define num_booting_cpus() 1
    diff --git a/kernel/smp.c b/kernel/smp.c
    index a081e6c..893e588 100644
    --- a/kernel/smp.c
    +++ b/kernel/smp.c
    @@ -730,3 +730,65 @@ void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
    put_cpu();
    }
    EXPORT_SYMBOL(on_each_cpu_mask);
    +
    +/*
    + * on_each_cpu_cond(): Call a function on each processor for which
    + * the supplied function cond_func returns true, optionally waiting
    + * for all the required CPUs to finish. This may include the local
    + * processor.
    + * @cond_func: A callback function that is passed a cpu id and
    + * the the info parameter. The function is called
    + * with preemption disabled. The function should
    + * return a blooean value indicating whether to IPI
    + * the specified CPU.
    + * @func: The function to run on all applicable CPUs.
    + * This must be fast and non-blocking.
    + * @info: An arbitrary pointer to pass to both functions.
    + * @wait: If true, wait (atomically) until function has
    + * completed on other CPUs.
    + * @gfp_flags: GFP flags to use when allocating the cpumask
    + * used internally by the function.
    + *
    + * The function might sleep if the GFP flags indicates a non
    + * atomic allocation is allowed.
    + *
    + * Preemption is disabled to protect against CPU going offline but not
    + * online. CPUs going online during the call will not be seen or sent
    + * an IPI.
    + *
    + * You must not call this function with disabled interrupts or
    + * from a hardware interrupt handler or from a bottom half handler.
    + */
    +void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
    + smp_call_func_t func, void *info, bool wait,
    + gfp_t gfp_flags)
    +{
    + cpumask_var_t cpus;
    + int cpu, ret;
    +
    + might_sleep_if(gfp_flags & __GFP_WAIT);
    +
    + if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) {
    + preempt_disable();
    + for_each_online_cpu(cpu)
    + if (cond_func(cpu, info))
    + cpumask_set_cpu(cpu, cpus);
    + on_each_cpu_mask(cpus, func, info, wait);
    + preempt_enable();
    + free_cpumask_var(cpus);
    + } else {
    + /*
    + * No free cpumask, bother. No matter, we'll
    + * just have to IPI them one by one.
    + */
    + preempt_disable();
    + for_each_online_cpu(cpu)
    + if (cond_func(cpu, info)) {
    + ret = smp_call_function_single(cpu, func,
    + info, wait);
    + WARN_ON_ONCE(!ret);
    + }
    + preempt_enable();
    + }
    +}
    +EXPORT_SYMBOL(on_each_cpu_cond);
    --
    1.7.0.4


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