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authorMichel Lespinasse <walken@google.com>2013-05-07 06:45:58 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-05-07 07:20:16 -0700
commit8cf5322ce69afea1fab6a6270db24d057d664798 (patch)
treea7b49b135dc7703a4a709562178a847fb9bc4f77 /lib
parent9b0fc9c09f1b262b7fe697eba6b05095d78850e5 (diff)
downloadlinux-linaro-stable-8cf5322ce69afea1fab6a6270db24d057d664798.tar.gz
rwsem: simplify __rwsem_do_wake
This is mostly for cleanup value: - We don't need several gotos to handle the case where the first waiter is a writer. Two simple tests will do (and generate very similar code). - In the remainder of the function, we know the first waiter is a reader, so we don't have to double check that. We can use do..while loops to iterate over the readers to wake (generates slightly better code). Signed-off-by: Michel Lespinasse <walken@google.com> Reviewed-by: Peter Hurley <peter@hurleysoftware.com> Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/rwsem-spinlock.c23
-rw-r--r--lib/rwsem.c26
2 files changed, 19 insertions, 30 deletions
diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
index 5f117f37ac0a..9be8a9144978 100644
--- a/lib/rwsem-spinlock.c
+++ b/lib/rwsem-spinlock.c
@@ -70,26 +70,17 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
- if (!wakewrite) {
- if (waiter->type == RWSEM_WAITING_FOR_WRITE)
- goto out;
- goto dont_wake_writers;
- }
-
- /*
- * as we support write lock stealing, we can't set sem->activity
- * to -1 here to indicate we get the lock. Instead, we wake it up
- * to let it go get it again.
- */
if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
- wake_up_process(waiter->task);
+ if (wakewrite)
+ /* Wake up a writer. Note that we do not grant it the
+ * lock - it will have to acquire it when it runs. */
+ wake_up_process(waiter->task);
goto out;
}
/* grant an infinite number of read locks to the front of the queue */
- dont_wake_writers:
woken = 0;
- while (waiter->type == RWSEM_WAITING_FOR_READ) {
+ do {
struct list_head *next = waiter->list.next;
list_del(&waiter->list);
@@ -99,10 +90,10 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
wake_up_process(tsk);
put_task_struct(tsk);
woken++;
- if (list_empty(&sem->wait_list))
+ if (next == &sem->wait_list)
break;
waiter = list_entry(next, struct rwsem_waiter, list);
- }
+ } while (waiter->type != RWSEM_WAITING_FOR_WRITE);
sem->activity += woken;
diff --git a/lib/rwsem.c b/lib/rwsem.c
index 0d50e46d5b0c..9a675fa9d78e 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -68,20 +68,17 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
signed long woken, loop, adjustment;
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
- if (waiter->type != RWSEM_WAITING_FOR_WRITE)
- goto readers_only;
-
- if (wake_type == RWSEM_WAKE_READ_OWNED)
- /* Another active reader was observed, so wakeup is not
- * likely to succeed. Save the atomic op.
- */
+ if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
+ if (wake_type != RWSEM_WAKE_READ_OWNED)
+ /* Wake writer at the front of the queue, but do not
+ * grant it the lock yet as we want other writers
+ * to be able to steal it. Readers, on the other hand,
+ * will block as they will notice the queued writer.
+ */
+ wake_up_process(waiter->task);
goto out;
+ }
- /* Wake up the writing waiter and let the task grab the sem: */
- wake_up_process(waiter->task);
- goto out;
-
- readers_only:
/* If we come here from up_xxxx(), another thread might have reached
* rwsem_down_failed_common() before we acquired the spinlock and
* woken up a waiter, making it now active. We prefer to check for
@@ -125,7 +122,8 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
rwsem_atomic_add(adjustment, sem);
next = sem->wait_list.next;
- for (loop = woken; loop > 0; loop--) {
+ loop = woken;
+ do {
waiter = list_entry(next, struct rwsem_waiter, list);
next = waiter->list.next;
tsk = waiter->task;
@@ -133,7 +131,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
- }
+ } while (--loop);
sem->wait_list.next = next;
next->prev = &sem->wait_list;