percpu: Resolve ambiguities in __get_cpu_var/cpumask_var_t

__get_cpu_var can paper over differences in the definitions of
cpumask_var_t and either use the address of the cpumask variable
directly or perform a fetch of the address of the struct cpumask
allocated elsewhere. This is important particularly when using per cpu
cpumask_var_t declarations because in one case we have an offset into
a per cpu area to handle and in the other case we need to fetch a
pointer from the offset.

This patch introduces a new macro

this_cpu_cpumask_var_ptr()

that is defined where cpumask_var_t is defined and performs the proper
actions. All use cases where __get_cpu_var is used with cpumask_var_t
are converted to the use of this_cpu_cpumask_var_ptr().

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

7 files changed, 17 insertions, 7 deletions

diff --git a/arch/x86/include/asm/perf_event_p4.h b/arch/x86/include/asm/perf_event_p4.h
index 85e13ccf15c4..d725382c2ae0 100644
--- a/arch/x86/include/asm/perf_event_p4.h
+++ b/arch/x86/include/asm/perf_event_p4.h
@@ -189,7 +189,7 @@ static inline int p4_ht_thread(int cpu)
 {
 #ifdef CONFIG_SMP
         if (smp_num_siblings == 2)
-                return cpu != cpumask_first(__get_cpu_var(cpu_sibling_map));
+                return cpu != cpumask_first(this_cpu_cpumask_var_ptr(cpu_sibling_map));
 #endif
         return 0;
 }
diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c
index 6ce600f9bc78..1f5d5f2ffae6 100644
--- a/arch/x86/kernel/apic/x2apic_cluster.c
+++ b/arch/x86/kernel/apic/x2apic_cluster.c
@@ -42,8 +42,7 @@ __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
          * We are to modify mask, so we need an own copy
          * and be sure it's manipulated with irq off.
          */
-        ipi_mask_ptr = __raw_get_cpu_var(ipi_mask);
-        cpumask_copy(ipi_mask_ptr, mask);
+        ipi_mask_ptr = this_cpu_cpumask_var_ptr(ipi_mask);
 
         /*
          * The idea is to send one IPI per cluster.
diff --git a/arch/x86/oprofile/op_model_p4.c b/arch/x86/oprofile/op_model_p4.c
index 98ab13058f89..ad1d91f475ab 100644
--- a/arch/x86/oprofile/op_model_p4.c
+++ b/arch/x86/oprofile/op_model_p4.c
@@ -372,7 +372,7 @@ static unsigned int get_stagger(void)
 {
 #ifdef CONFIG_SMP
         int cpu = smp_processor_id();
-        return cpu != cpumask_first(__get_cpu_var(cpu_sibling_map));
+        return cpu != cpumask_first(this_cpu_cpumask_var_ptr(cpu_sibling_map));
 #endif
         return 0;
 }
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 2997af6d2ccd..0a9a6da21e74 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -666,10 +666,19 @@ static inline size_t cpumask_size(void)
  *
  * This code makes NR_CPUS length memcopy and brings to a memory corruption.
  * cpumask_copy() provide safe copy functionality.
+ *
+ * Note that there is another evil here: If you define a cpumask_var_t
+ * as a percpu variable then the way to obtain the address of the cpumask
+ * structure differently influences what this_cpu_* operation needs to be
+ * used. Please use this_cpu_cpumask_var_t in those cases. The direct use
+ * of this_cpu_ptr() or this_cpu_read() will lead to failures when the
+ * other type of cpumask_var_t implementation is configured.
  */
 #ifdef CONFIG_CPUMASK_OFFSTACK
 typedef struct cpumask *cpumask_var_t;
 
+#define this_cpu_cpumask_var_ptr(x) this_cpu_read(x)
+
 bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node);
 bool alloc_cpumask_var(cpumask_var_t *mask, gfp_t flags);
 bool zalloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node);
@@ -681,6 +690,8 @@ void free_bootmem_cpumask_var(cpumask_var_t mask);
 #else
 typedef struct cpumask cpumask_var_t[1];
 
+#define this_cpu_cpumask_var_ptr(x) this_cpu_ptr(x)
+
 static inline bool alloc_cpumask_var(cpumask_var_t *mask, gfp_t flags)
 {
         return true;
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 255ce138b652..4a608cfaecbd 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1158,7 +1158,7 @@ static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
 static int find_later_rq(struct task_struct *task)
 {
         struct sched_domain *sd;
-        struct cpumask *later_mask = __get_cpu_var(local_cpu_mask_dl);
+        struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
         int this_cpu = smp_processor_id();
         int best_cpu, cpu = task_cpu(task);
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bfa3c86d0d68..197d659c144c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6539,7 +6539,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
         struct sched_group *group;
         struct rq *busiest;
         unsigned long flags;
-        struct cpumask *cpus = __get_cpu_var(load_balance_mask);
+        struct cpumask *cpus = this_cpu_cpumask_var_ptr(load_balance_mask);
 
         struct lb_env env = {
                 .sd             = sd,
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 5f6edca4fafd..a4c50fce9b90 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1526,7 +1526,7 @@ static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);
 static int find_lowest_rq(struct task_struct *task)
 {
         struct sched_domain *sd;
-        struct cpumask *lowest_mask = __get_cpu_var(local_cpu_mask);
+        struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);
         int this_cpu = smp_processor_id();
         int cpu      = task_cpu(task);