linux-kernel - [PATCH tip/core/rcu 03/15] preempt: Cleanup PREEMPT

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Date:   Mon, 28 Sep 2020 16:30:50 -0700
From:   paulmck@...nel.org
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org, mhocko@...nel.org,
        mgorman@...hsingularity.net, torvalds@...ux-foundation.org,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH tip/core/rcu 03/15] preempt: Cleanup PREEMPT_COUNT leftovers

From: Thomas Gleixner <tglx@...utronix.de>

CONFIG_PREEMPT_COUNT is now unconditionally enabled and will be
removed. Cleanup the leftovers before doing so.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 include/linux/preempt.h | 37 ++++---------------------------------
 1 file changed, 4 insertions(+), 33 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 7d9c1c0..513769b 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -56,8 +56,7 @@
 #define PREEMPT_DISABLED	(PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
 
 /*
- * Disable preemption until the scheduler is running -- use an unconditional
- * value so that it also works on !PREEMPT_COUNT kernels.
+ * Disable preemption until the scheduler is running.
  *
  * Reset by start_kernel()->sched_init()->init_idle()->init_idle_preempt_count().
  */
@@ -69,7 +68,6 @@
  *
  *    preempt_count() == 2*PREEMPT_DISABLE_OFFSET
  *
- * Note: PREEMPT_DISABLE_OFFSET is 0 for !PREEMPT_COUNT kernels.
  * Note: See finish_task_switch().
  */
 #define FORK_PREEMPT_COUNT	(2*PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
@@ -106,11 +104,7 @@
 /*
  * The preempt_count offset after preempt_disable();
  */
-#if defined(CONFIG_PREEMPT_COUNT)
-# define PREEMPT_DISABLE_OFFSET	PREEMPT_OFFSET
-#else
-# define PREEMPT_DISABLE_OFFSET	0
-#endif
+#define PREEMPT_DISABLE_OFFSET	PREEMPT_OFFSET
 
 /*
  * The preempt_count offset after spin_lock()
@@ -122,8 +116,8 @@
  *
  *  spin_lock_bh()
  *
- * Which need to disable both preemption (CONFIG_PREEMPT_COUNT) and
- * softirqs, such that unlock sequences of:
+ * Which need to disable both preemption and softirqs, such that unlock
+ * sequences of:
  *
  *  spin_unlock();
  *  local_bh_enable();
@@ -164,8 +158,6 @@ extern void preempt_count_sub(int val);
 #define preempt_count_inc() preempt_count_add(1)
 #define preempt_count_dec() preempt_count_sub(1)
 
-#ifdef CONFIG_PREEMPT_COUNT
-
 #define preempt_disable() \
 do { \
 	preempt_count_inc(); \
@@ -231,27 +223,6 @@ do { \
 	__preempt_count_dec(); \
 } while (0)
 
-#else /* !CONFIG_PREEMPT_COUNT */
-
-/*
- * Even if we don't have any preemption, we need preempt disable/enable
- * to be barriers, so that we don't have things like get_user/put_user
- * that can cause faults and scheduling migrate into our preempt-protected
- * region.
- */
-#define preempt_disable()			barrier()
-#define sched_preempt_enable_no_resched()	barrier()
-#define preempt_enable_no_resched()		barrier()
-#define preempt_enable()			barrier()
-#define preempt_check_resched()			do { } while (0)
-
-#define preempt_disable_notrace()		barrier()
-#define preempt_enable_no_resched_notrace()	barrier()
-#define preempt_enable_notrace()		barrier()
-#define preemptible()				0
-
-#endif /* CONFIG_PREEMPT_COUNT */
-
 #ifdef MODULE
 /*
  * Modules have no business playing preemption tricks.
-- 
2.9.5