linux-kernel - [PATCH 1/6] locking/rwsem: Minor code refactoring in rwsem_mark

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Date:   Thu, 23 Feb 2023 13:26:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     longman@...hat.com, mingo@...hat.com, will@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        boqun.feng@...il.com
Subject: [PATCH 1/6] locking/rwsem: Minor code refactoring in rwsem_mark_wake()

From: Waiman Long <longman@...hat.com>

Rename "oldcount" to "count" as it is not always old count value.
Also make some minor code refactoring to reduce indentation. There
is no functional change.

Signed-off-by: Waiman Long <longman@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20230216210933.1169097-2-longman@redhat.com
---
 kernel/locking/rwsem.c |   44 ++++++++++++++++++++++----------------------
 1 file changed, 22 insertions(+), 22 deletions(-)

--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -40,7 +40,7 @@
  *
  * When the rwsem is reader-owned and a spinning writer has timed out,
  * the nonspinnable bit will be set to disable optimistic spinning.
-
+ *
  * When a writer acquires a rwsem, it puts its task_struct pointer
  * into the owner field. It is cleared after an unlock.
  *
@@ -413,7 +413,7 @@ static void rwsem_mark_wake(struct rw_se
 			    struct wake_q_head *wake_q)
 {
 	struct rwsem_waiter *waiter, *tmp;
-	long oldcount, woken = 0, adjustment = 0;
+	long count, woken = 0, adjustment = 0;
 	struct list_head wlist;
 
 	lockdep_assert_held(&sem->wait_lock);
@@ -424,22 +424,23 @@ static void rwsem_mark_wake(struct rw_se
 	 */
 	waiter = rwsem_first_waiter(sem);
 
-	if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
-		if (wake_type == RWSEM_WAKE_ANY) {
-			/*
-			 * Mark writer at the front of the queue for wakeup.
-			 * Until the task is actually later awoken later by
-			 * the caller, other writers are able to steal it.
-			 * Readers, on the other hand, will block as they
-			 * will notice the queued writer.
-			 */
-			wake_q_add(wake_q, waiter->task);
-			lockevent_inc(rwsem_wake_writer);
-		}
+	if (waiter->type != RWSEM_WAITING_FOR_WRITE)
+		goto wake_readers;
 
-		return;
+	if (wake_type == RWSEM_WAKE_ANY) {
+		/*
+		 * Mark writer at the front of the queue for wakeup.
+		 * Until the task is actually later awoken later by
+		 * the caller, other writers are able to steal it.
+		 * Readers, on the other hand, will block as they
+		 * will notice the queued writer.
+		 */
+		wake_q_add(wake_q, waiter->task);
+		lockevent_inc(rwsem_wake_writer);
 	}
+	return;
 
+wake_readers:
 	/*
 	 * No reader wakeup if there are too many of them already.
 	 */
@@ -455,15 +456,15 @@ static void rwsem_mark_wake(struct rw_se
 		struct task_struct *owner;
 
 		adjustment = RWSEM_READER_BIAS;
-		oldcount = atomic_long_fetch_add(adjustment, &sem->count);
-		if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
+		count = atomic_long_fetch_add(adjustment, &sem->count);
+		if (unlikely(count & RWSEM_WRITER_MASK)) {
 			/*
 			 * When we've been waiting "too" long (for writers
 			 * to give up the lock), request a HANDOFF to
 			 * force the issue.
 			 */
 			if (time_after(jiffies, waiter->timeout)) {
-				if (!(oldcount & RWSEM_FLAG_HANDOFF)) {
+				if (!(count & RWSEM_FLAG_HANDOFF)) {
 					adjustment -= RWSEM_FLAG_HANDOFF;
 					lockevent_inc(rwsem_rlock_handoff);
 				}
@@ -524,21 +525,21 @@ static void rwsem_mark_wake(struct rw_se
 	adjustment = woken * RWSEM_READER_BIAS - adjustment;
 	lockevent_cond_inc(rwsem_wake_reader, woken);
 
-	oldcount = atomic_long_read(&sem->count);
+	count = atomic_long_read(&sem->count);
 	if (list_empty(&sem->wait_list)) {
 		/*
 		 * Combined with list_move_tail() above, this implies
 		 * rwsem_del_waiter().
 		 */
 		adjustment -= RWSEM_FLAG_WAITERS;
-		if (oldcount & RWSEM_FLAG_HANDOFF)
+		if (count & RWSEM_FLAG_HANDOFF)
 			adjustment -= RWSEM_FLAG_HANDOFF;
 	} else if (woken) {
 		/*
 		 * When we've woken a reader, we no longer need to force
 		 * writers to give up the lock and we can clear HANDOFF.
 		 */
-		if (oldcount & RWSEM_FLAG_HANDOFF)
+		if (count & RWSEM_FLAG_HANDOFF)
 			adjustment -= RWSEM_FLAG_HANDOFF;
 	}
 
@@ -844,7 +845,6 @@ static bool rwsem_optimistic_spin(struct
 		 * Try to acquire the lock
 		 */
 		taken = rwsem_try_write_lock_unqueued(sem);
-
 		if (taken)
 			break;