smp: add func to IPI cpus based on parameter func

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.

[akpm@linux-foundation.org: s/gfpflags/gfp_flags/]
[akpm@linux-foundation.org: avoid double-evaluation of `info' (per Michal), parenthesise evaluation of `cond_func']
[akpm@linux-foundation.org: s/CPU/CPUs, use all 80 cols in comment]
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
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: Avi Kivity <avi@redhat.com>
Acked-by: Michal Nazarewicz <mina86@mina86.org>
Cc: Kosaki Motohiro <kosaki.motohiro@gmail.com>
Cc: Milton Miller <miltonm@bga.com>
Reviewed-by: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 85 insertions, 0 deletions

diff --git a/include/linux/smp.h b/include/linux/smp.h
index d0adb7898d54..10530d92c04b 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 +162,21 @@ 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 a081e6ce0e0a..2f8b10ecf759 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -730,3 +730,64 @@ 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 CPUs 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);