kernel/futex: Kill rt_mutex_next_owner()

Update wake_futex_pi() and kill the call altogether. This is possible because:

(i) The case of fixup_owner() in which the pi_mutex was stolen from the
signaled enqueued top-waiter which fails to trylock and doesn't see a
current owner of the rtmutex but needs to acknowledge an non-enqueued
higher priority waiter, which is the other alternative. This used to be
handled by rt_mutex_next_owner(), which guaranteed fixup_pi_state_owner('newowner')
never to be nil. Nowadays the logic is handled by an EAGAIN loop, without
the need of rt_mutex_next_owner(). Specifically:

    c1e2f0eaf015 (futex: Avoid violating the 10th rule of futex)
    9f5d1c336a10 (futex: Handle transient "ownerless" rtmutex state correctly)

(ii) rt_mutex_next_owner() and rt_mutex_top_waiter() are semantically
equivalent, as of:

    c28d62cf52d7 (locking/rtmutex: Handle non enqueued waiters gracefully in remove_waiter())

So instead of keeping the call around, just use the good ole rt_mutex_top_waiter().
No change in semantics.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210226175029.50335-1-dave@stgolabs.net

1 files changed, 0 insertions, 1 deletions

diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index ca6fb489007b..a5007f00c1b7 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -130,7 +130,6 @@ enum rtmutex_chainwalk {
 /*
  * PI-futex support (proxy locking functions, etc.):
  */
-extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock);
 extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
 				       struct task_struct *proxy_owner);
 extern void rt_mutex_proxy_unlock(struct rt_mutex *lock);