sched: Introduce preempt_count accessor functions

Replace the single preempt_count() 'function' that's an lvalue with
two proper functions:

 preempt_count() - returns the preempt_count value as rvalue
 preempt_count_set() - Allows setting the preempt-count value

Also provide preempt_count_ptr() as a convenience wrapper to implement
all modifying operations.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-orxrbycjozopqfhb4dxdkdvb@git.kernel.org
[ Fixed build failure. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

7 files changed, 30 insertions, 18 deletions

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index f5d4723cdb3d..eaac52a8fe6a 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -10,19 +10,32 @@
 #include <linux/linkage.h>
 #include <linux/list.h>
 
+static __always_inline int preempt_count(void)
+{
+        return current_thread_info()->preempt_count;
+}
+
+static __always_inline int *preempt_count_ptr(void)
+{
+        return &current_thread_info()->preempt_count;
+}
+
+static __always_inline void preempt_count_set(int pc)
+{
+        *preempt_count_ptr() = pc;
+}
+
 #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
   extern void add_preempt_count(int val);
   extern void sub_preempt_count(int val);
 #else
-# define add_preempt_count(val) do { preempt_count() += (val); } while (0)
-# define sub_preempt_count(val) do { preempt_count() -= (val); } while (0)
+# define add_preempt_count(val) do { *preempt_count_ptr() += (val); } while (0)
+# define sub_preempt_count(val) do { *preempt_count_ptr() -= (val); } while (0)
 #endif
 
 #define inc_preempt_count() add_preempt_count(1)
 #define dec_preempt_count() sub_preempt_count(1)
 
-#define preempt_count() (current_thread_info()->preempt_count)
-
 #ifdef CONFIG_PREEMPT
 
 asmlinkage void preempt_schedule(void);
@@ -81,9 +94,9 @@ do { \
 
 /* For debugging and tracer internals only! */
 #define add_preempt_count_notrace(val)                  \
-        do { preempt_count() += (val); } while (0)
+        do { *preempt_count_ptr() += (val); } while (0)
 #define sub_preempt_count_notrace(val)                  \
-        do { preempt_count() -= (val); } while (0)
+        do { *preempt_count_ptr() -= (val); } while (0)
 #define inc_preempt_count_notrace() add_preempt_count_notrace(1)
 #define dec_preempt_count_notrace() sub_preempt_count_notrace(1)
 
diff --git a/init/main.c b/init/main.c
index af310afbef28..7cc4b7889a88 100644
--- a/init/main.c
+++ b/init/main.c
@@ -692,7 +692,7 @@ int __init_or_module do_one_initcall(initcall_t fn)
 
         if (preempt_count() != count) {
                 sprintf(msgbuf, "preemption imbalance ");
-                preempt_count() = count;
+                preempt_count_set(count);
         }
         if (irqs_disabled()) {
                 strlcat(msgbuf, "disabled interrupts ", sizeof(msgbuf));
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 242da0c03aba..fe89afac4d09 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2219,7 +2219,7 @@ void __kprobes add_preempt_count(int val)
         if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
                 return;
 #endif
-        preempt_count() += val;
+        add_preempt_count_notrace(val);
 #ifdef CONFIG_DEBUG_PREEMPT
         /*
          * Spinlock count overflowing soon?
@@ -2250,7 +2250,7 @@ void __kprobes sub_preempt_count(int val)
 
         if (preempt_count() == val)
                 trace_preempt_on(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
-        preempt_count() -= val;
+        sub_preempt_count_notrace(val);
 }
 EXPORT_SYMBOL(sub_preempt_count);
 
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 53cc09ceb0b8..a90de70cf1f3 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -106,7 +106,7 @@ static void __local_bh_disable(unsigned long ip, unsigned int cnt)
          * We must manually increment preempt_count here and manually
          * call the trace_preempt_off later.
          */
-        preempt_count() += cnt;
+        add_preempt_count_notrace(cnt);
         /*
          * Were softirqs turned off above:
          */
@@ -256,7 +256,7 @@ restart:
                                        " exited with %08x?\n", vec_nr,
                                        softirq_to_name[vec_nr], h->action,
                                        prev_count, preempt_count());
-                                preempt_count() = prev_count;
+                                preempt_count_set(prev_count);
                         }
 
                         rcu_bh_qs(cpu);
diff --git a/kernel/timer.c b/kernel/timer.c
index 4296d13db3d1..6582b82fa966 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1092,7 +1092,7 @@ static int cascade(struct tvec_base *base, struct tvec *tv, int index)
 static void call_timer_fn(struct timer_list *timer, void (*fn)(unsigned long),
                           unsigned long data)
 {
-        int preempt_count = preempt_count();
+        int count = preempt_count();
 
 #ifdef CONFIG_LOCKDEP
         /*
@@ -1119,16 +1119,16 @@ static void call_timer_fn(struct timer_list *timer, void (*fn)(unsigned long),
 
         lock_map_release(&lockdep_map);
 
-        if (preempt_count != preempt_count()) {
+        if (count != preempt_count()) {
                 WARN_ONCE(1, "timer: %pF preempt leak: %08x -> %08x\n",
-                          fn, preempt_count, preempt_count());
+                          fn, count, preempt_count());
                 /*
                  * Restore the preempt count. That gives us a decent
                  * chance to survive and extract information. If the
                  * callback kept a lock held, bad luck, but not worse
                  * than the BUG() we had.
                  */
-                preempt_count() = preempt_count;
+                preempt_count_set(count);
         }
 }
 
diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 6dc09d8f4c24..872a15a2a637 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -1002,7 +1002,7 @@ static void dotest(void (*testcase_fn)(void), int expected, int lockclass_mask)
          * Some tests (e.g. double-unlock) might corrupt the preemption
          * count, so restore it:
          */
-        preempt_count() = saved_preempt_count;
+        preempt_count_set(saved_preempt_count);
 #ifdef CONFIG_TRACE_IRQFLAGS
         if (softirq_count())
                 current->softirqs_enabled = 0;
diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index 4c0d0e51d49e..04abe53f12a1 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -9,10 +9,9 @@
 
 notrace unsigned int debug_smp_processor_id(void)
 {
-        unsigned long preempt_count = preempt_count();
         int this_cpu = raw_smp_processor_id();
 
-        if (likely(preempt_count))
+        if (likely(preempt_count()))
                 goto out;
 
         if (irqs_disabled())