Message-Id: <20190812134859.16061-1-sst2005@gmail.com>
Date:   Mon, 12 Aug 2019 19:18:59 +0530
From:   Satendra Singh Thakur <sst2005@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Satendra Singh Thakur <sst2005@...il.com>,
        Satendra Singh Thakur <satendrasingh.thakur@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1] [semaphore] Removed redundant code from semaphore's down family of function

-The semaphore code has four funcs
down,
down_interruptible,
down_killable,
down_timeout
-These four funcs have almost similar code except that
they all call lower level function __down_xyz.
-This lower level func in-turn call inline func
__down_common with appropriate arguments.
-This patch creates a common macro for above family of funcs
so that duplicate code is eliminated.
-Also, __down_common has been made noinline so that code is
functionally similar to previous one
-For example, earlier down_killable would call __down_killable
, which in-turn would call inline func __down_common
Now, down_killable calls noinline __down_common directly
through a macro
-The funcs __down_interruptible, __down_killable etc have been
removed as they were just wrapper to __down_common

Signed-off-by: Satendra Singh Thakur <satendrasingh.thakur@....com>
---
 v1: removed disclaimer appended automatically by company mail policy

 kernel/locking/semaphore.c | 107 +++++++++++++------------------------
 1 file changed, 38 insertions(+), 69 deletions(-)

diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index d9dd94defc0a..0468bc335908 100644
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -33,11 +33,33 @@
 #include <linux/spinlock.h>
 #include <linux/ftrace.h>
 
-static noinline void __down(struct semaphore *sem);
-static noinline int __down_interruptible(struct semaphore *sem);
-static noinline int __down_killable(struct semaphore *sem);
-static noinline int __down_timeout(struct semaphore *sem, long timeout);
+static noinline int __sched __down_common(struct semaphore *sem, long state,
+								long timeout);
 static noinline void __up(struct semaphore *sem);
+/**
+ * down_common - acquire the semaphore
+ * @sem: the semaphore to be acquired
+ * @state: new state of the task
+ * @timeout: either MAX_SCHEDULE_TIMEOUT or actual specified
+ * timeout
+ * Acquires the semaphore. If no more tasks are allowed to
+ * acquire the semaphore, calling this macro will put the task
+ * to sleep until the semaphore is released.
+ *
+ * This internally calls another func __down_common.
+ */
+#define down_common(sem, state, timeout)	\
+({	\
+	int ret = 0;	\
+	unsigned long flags;	\
+	raw_spin_lock_irqsave(&(sem)->lock, flags);	\
+	if (likely((sem)->count > 0))	\
+		(sem)->count--;	\
+	else	\
+		ret = __down_common(sem, state, timeout);	\
+	raw_spin_unlock_irqrestore(&(sem)->lock, flags);	\
+	ret;	\
+})
 
 /**
  * down - acquire the semaphore
@@ -52,14 +74,7 @@ static noinline void __up(struct semaphore *sem);
  */
 void down(struct semaphore *sem)
 {
-	unsigned long flags;
-
-	raw_spin_lock_irqsave(&sem->lock, flags);
-	if (likely(sem->count > 0))
-		sem->count--;
-	else
-		__down(sem);
-	raw_spin_unlock_irqrestore(&sem->lock, flags);
+	down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
 }
 EXPORT_SYMBOL(down);
 
@@ -74,17 +89,7 @@ EXPORT_SYMBOL(down);
  */
 int down_interruptible(struct semaphore *sem)
 {
-	unsigned long flags;
-	int result = 0;
-
-	raw_spin_lock_irqsave(&sem->lock, flags);
-	if (likely(sem->count > 0))
-		sem->count--;
-	else
-		result = __down_interruptible(sem);
-	raw_spin_unlock_irqrestore(&sem->lock, flags);
-
-	return result;
+	return down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
 }
 EXPORT_SYMBOL(down_interruptible);
 
@@ -100,17 +105,7 @@ EXPORT_SYMBOL(down_interruptible);
  */
 int down_killable(struct semaphore *sem)
 {
-	unsigned long flags;
-	int result = 0;
-
-	raw_spin_lock_irqsave(&sem->lock, flags);
-	if (likely(sem->count > 0))
-		sem->count--;
-	else
-		result = __down_killable(sem);
-	raw_spin_unlock_irqrestore(&sem->lock, flags);
-
-	return result;
+	return down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
 }
 EXPORT_SYMBOL(down_killable);
 
@@ -154,17 +149,7 @@ EXPORT_SYMBOL(down_trylock);
  */
 int down_timeout(struct semaphore *sem, long timeout)
 {
-	unsigned long flags;
-	int result = 0;
-
-	raw_spin_lock_irqsave(&sem->lock, flags);
-	if (likely(sem->count > 0))
-		sem->count--;
-	else
-		result = __down_timeout(sem, timeout);
-	raw_spin_unlock_irqrestore(&sem->lock, flags);
-
-	return result;
+	return down_common(sem, TASK_UNINTERRUPTIBLE, timeout);
 }
 EXPORT_SYMBOL(down_timeout);
 
@@ -196,12 +181,15 @@ struct semaphore_waiter {
 	bool up;
 };
 
-/*
- * Because this function is inlined, the 'state' parameter will be
- * constant, and thus optimised away by the compiler.  Likewise the
- * 'timeout' parameter for the cases without timeouts.
+/**
+ * __down_common - Adds the current task to wait list
+ * puts the task to sleep until signal, timeout or up flag
+ * @sem: the semaphore to be acquired
+ * @state: the state of the calling task
+ * @timeout: either MAX_SCHEDULE_TIMEOUT or actual specified
+ * timeout
  */
-static inline int __sched __down_common(struct semaphore *sem, long state,
+static noinline int __sched __down_common(struct semaphore *sem, long state,
 								long timeout)
 {
 	struct semaphore_waiter waiter;
@@ -232,25 +220,6 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
 	return -EINTR;
 }
 
-static noinline void __sched __down(struct semaphore *sem)
-{
-	__down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
-}
-
-static noinline int __sched __down_interruptible(struct semaphore *sem)
-{
-	return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
-}
-
-static noinline int __sched __down_killable(struct semaphore *sem)
-{
-	return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
-}
-
-static noinline int __sched __down_timeout(struct semaphore *sem, long timeout)
-{
-	return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout);
-}
 
 static noinline void __sched __up(struct semaphore *sem)
 {
-- 
2.17.1

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