[PATCH v2 1/3] locking/rwsem: Minor code refactoring in rwsem_mark_wake()

Waiman Long
2023-02-16T21:10:39Z

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@redhat.com>
---
kernel/locking/rwsem.c | 44 +++++++++++++++++++++---------------------
1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index acb5a50309a1..e589f69793df 100644
--- 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_semaphore *sem,
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_semaphore *sem,
*/
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_semaphore *sem,
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_semaphore *sem,
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 rw_semaphore *sem)
* Try to acquire the lock
*/
taken = rwsem_try_write_lock_unqueued(sem);
-
if (taken)
break;

--
2.31.1