[RFC][PATCH 1/5] sched: Introduce preempt_count accessor functions

Peter Zijlstra
2013-08-14T13:41:12Z

[-- Attachment #1: peterz-preempt_count-accessors.patch --]
[-- Type: text/plain, Size: 5025 bytes --]

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_ptr() - returns a pointer to the preempt_count

Then change all sites that modify the preempt count to use
preempt_count_ptr().

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-7zr0ph7cvibcp96lw02ln9nr@git.kernel.org
---
include/linux/preempt.h | 20 ++++++++++++++------
init/main.c | 2 +-
kernel/sched/core.c | 4 ++--
kernel/softirq.c | 4 ++--
kernel/timer.c | 8 ++++----
lib/smp_processor_id.c | 3 +--
6 files changed, 24 insertions(+), 17 deletions(-)

--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -10,19 +10,27 @@
#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;
+}
+
#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 +89,9 @@ 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)

--- a/init/main.c
+++ b/init/main.c
@@ -690,7 +690,7 @@ int __init_or_module do_one_initcall(ini

if (preempt_count() != count) {
sprintf(msgbuf, "preemption imbalance ");
- preempt_count() = count;
+ *preempt_count_ptr() = count;
}
if (irqs_disabled()) {
strlcat(msgbuf, "disabled interrupts ", sizeof(msgbuf));
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2233,7 +2233,7 @@ void __kprobes add_preempt_count(int val
if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
return;
#endif
- preempt_count() += val;
+ *preempt_count_ptr() += val;
#ifdef CONFIG_DEBUG_PREEMPT
/*
* Spinlock count overflowing soon?
@@ -2264,7 +2264,7 @@ void __kprobes sub_preempt_count(int val

if (preempt_count() == val)
trace_preempt_on(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
- preempt_count() -= val;
+ *preempt_count_ptr() -= val;
}
EXPORT_SYMBOL(sub_preempt_count);

--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -106,7 +106,7 @@ static void __local_bh_disable(unsigned
* We must manually increment preempt_count here and manually
* call the trace_preempt_off later.
*/
- preempt_count() += cnt;
+ *preempt_count_ptr() += cnt;
/*
* Were softirqs turned off above:
*/
@@ -256,7 +256,7 @@ asmlinkage void __do_softirq(void)
" exited with %08x?\n", vec_nr,
softirq_to_name[vec_nr], h->action,
prev_count, preempt_count());
- preempt_count() = prev_count;
+ *preempt_count_ptr() = prev_count;
}

rcu_bh_qs(cpu);
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1092,7 +1092,7 @@ static int cascade(struct tvec_base *bas
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_l

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_ptr() = count;
}
}

--- 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())