locking/rwsem: Simplify the is-owner-spinnable checks

Add the trivial owner_on_cpu() helper for rwsem_can_spin_on_owner() and
rwsem_spin_on_owner(), it also allows to make rwsem_can_spin_on_owner()
a bit more clear.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180518165534.GA22348@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 13 insertions, 12 deletions

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index a90336779375..3064c50e181e 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -347,6 +347,15 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
         }
 }
 
+static inline bool owner_on_cpu(struct task_struct *owner)
+{
+        /*
+         * As lock holder preemption issue, we both skip spinning if
+         * task is not on cpu or its cpu is preempted
+         */
+        return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
+}
+
 static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
 {
         struct task_struct *owner;
@@ -359,17 +368,10 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
 
         rcu_read_lock();
         owner = READ_ONCE(sem->owner);
-        if (!owner || !is_rwsem_owner_spinnable(owner)) {
-                ret = !owner;   /* !owner is spinnable */
-                goto done;
+        if (owner) {
+                ret = is_rwsem_owner_spinnable(owner) &&
+                      owner_on_cpu(owner);
         }
-
-        /*
-         * As lock holder preemption issue, we both skip spinning if task is not
-         * on cpu or its cpu is preempted
-         */
-        ret = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
-done:
         rcu_read_unlock();
         return ret;
 }
@@ -398,8 +400,7 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
                  * abort spinning when need_resched or owner is not running or
                  * owner's cpu is preempted.
                  */
-                if (!owner->on_cpu || need_resched() ||
-                                vcpu_is_preempted(task_cpu(owner))) {
+                if (need_resched() || !owner_on_cpu(owner)) {
                         rcu_read_unlock();
                         return false;
                 }