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>
Acked-by: Peter Zijlstra <redacted>
CC: Chris Metcalf <redacted>
CC: Christoph Lameter <redacted>
CC: Frederic Weisbecker <redacted>
CC: Russell King <redacted>
CC: linux-mm@kvack.org
CC: Pekka Enberg <penberg@kernel.org>
CC: Matt Mackall <redacted>
CC: Sasha Levin <redacted>
CC: Rik van Riel <redacted>
CC: Andi Kleen <redacted>
CC: Alexander Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
CC: Avi Kivity <redacted>
CC: Michal Nazarewicz <redacted>
CC: Kosaki Motohiro <redacted>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Milton Miller <redacted>
---
 include/linux/smp.h |   24 ++++++++++++++++++++
 kernel/smp.c        |   60 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+), 0 deletions(-)

diff --git a/include/linux/smp.h b/include/linux/smp.h
index d0adb78..da4d034 100644
--- a/include/linux/smp.h
+++ b/include/linux/smp.h

@@ -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 {						\