From: Frederic Weisbecker <fweisbec@gmail.com>
To: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: [RFC PATCH 4/4] sched: Account PREEMPT_ACTIVE context as atomic
Date: Wed, 28 Jan 2015 01:24:12 +0100 [thread overview]
Message-ID: <1422404652-29067-5-git-send-email-fweisbec@gmail.com> (raw)
In-Reply-To: <1422404652-29067-1-git-send-email-fweisbec@gmail.com>
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
next prev parent reply other threads:[~2015-01-28 0:24 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-28 0:24 [PATCH 0/4] sched: schedule/preempt optimizations and cleanups Frederic Weisbecker
2015-01-28 0:24 ` [PATCH 1/4] sched: Pull resched loop to __schedule() callers Frederic Weisbecker
2015-02-04 14:36 ` [tip:sched/core] " tip-bot for Frederic Weisbecker
2015-01-28 0:24 ` [RFC PATCH 2/4] sched: Use traced preempt count operations to toggle PREEMPT_ACTIVE Frederic Weisbecker
2015-01-28 1:42 ` Steven Rostedt
2015-01-28 13:59 ` Frederic Weisbecker
2015-01-28 15:04 ` Steven Rostedt
2015-01-28 15:42 ` Peter Zijlstra
2015-02-02 17:22 ` Frederic Weisbecker
2015-01-28 0:24 ` [PATCH 3/4] sched: Pull preemption disablement to __schedule() caller Frederic Weisbecker
2015-01-28 15:50 ` Peter Zijlstra
2015-02-02 17:53 ` Frederic Weisbecker
2015-02-03 10:53 ` Peter Zijlstra
2015-02-04 17:31 ` Frederic Weisbecker
2015-02-04 17:48 ` Peter Zijlstra
2015-01-28 0:24 ` Frederic Weisbecker [this message]
2015-01-28 15:46 ` [RFC PATCH 4/4] sched: Account PREEMPT_ACTIVE context as atomic Peter Zijlstra
2015-02-02 17:29 ` Frederic Weisbecker
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