[RFC PATCH 4/4] sched: Account PREEMPT_ACTIVE context as atomic

Frederic Weisbecker
2015-01-28T00:24:30Z

PREEMPT_ACTIVE implies non-preemptible context and thus atomic context
despite what in_atomic*() APIs reports about it. These functions
shouldn't ignore this value like they are currently doing.

It appears that these APIs were ignoring PREEMPT_ACTIVE in order to
ease the check in schedule_debug(). Meanwhile it is sufficient to rely
on PREEMPT_ACTIVE in order to disable preemption in __schedule().

So lets fix the in_atomic*() APIs and simplify the preempt count ops
on __schedule() callers.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
include/linux/preempt_mask.h | 4 ++--
kernel/sched/core.c | 12 ++++++------
2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/linux/preempt_mask.h b/include/linux/preempt_mask.h
index dbeec4d..4b8c9b7 100644
--- a/include/linux/preempt_mask.h
+++ b/include/linux/preempt_mask.h
@@ -99,14 +99,14 @@
* used in the general case to determine whether sleeping is possible.
* Do not use in_atomic() in driver code.
*/
-#define in_atomic() ((preempt_count() & ~PREEMPT_ACTIVE) != 0)
+#define in_atomic() (preempt_count() != 0)

/*
* Check whether we were atomic before we did preempt_disable():
* (used by the scheduler, *after* releasing the kernel lock)
*/
#define in_atomic_preempt_off() \
- ((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET)
+ (preempt_count() & ~(PREEMPT_ACTIVE | PREEMPT_CHECK_OFFSET))

#ifdef CONFIG_PREEMPT_COUNT
# define preemptible() (preempt_count() == 0 && !irqs_disabled())
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1c0e5b1..c017a5f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2882,9 +2882,9 @@ void __sched schedule_preempt_disabled(void)
static void preempt_schedule_common(void)
{
do {
- preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
+ preempt_count_add(PREEMPT_ACTIVE);
__schedule();
- preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
+ preempt_count_sub(PREEMPT_ACTIVE);

/*
* Check again in case we missed a preemption opportunity
@@ -2937,7 +2937,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void)
return;

do {
- preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
+ preempt_count_add(PREEMPT_ACTIVE);
/*
* Needs preempt disabled in case user_exit() is traced
* and the tracer calls preempt_enable_notrace() causing
@@ -2946,7 +2946,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void)
prev_ctx = exception_enter();
__schedule();
exception_exit(prev_ctx);
- preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
+ preempt_count_sub(PREEMPT_ACTIVE);
barrier();
} while (need_resched());
}
@@ -2971,11 +2971,11 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
prev_state = exception_enter();

do {
- preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
+ preempt_count_add(PREEMPT_ACTIVE);
local_irq_enable();
__schedule();
local_irq_disable();
- preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
+ preempt_count_sub(PREEMPT_ACTIVE);

/*
* Check again in case we missed a preemption opportunity
--
2.1.4