futex/requeue: Revert "Prevent NULL pointer dereference in remove_waiter() on self-deadlock""

The commit cited below should not have been merged. It attemted to fix an
existing problem ansd thereby introduced new problems by keeping the
pi_state in state Q_REQUEUE_PI_IN_PROGRESS and leaking it.

Based on the commit description the intention was to handle the case
when task_blocks_on_rt_mutex() returns -EDEADLK and the following
remove_waiter() dereferences the NULL pointer in waiter->task.

That is already handled by Davidlohr in commit 40a25d5
("locking/rtmutex: Skip remove_waiter() when waiter is not enqueued") and
requires no further acting.

Revert the commit breaking the "waiter == owner" case again.

Fixes: 74e1442 ("futex/requeue: Prevent NULL pointer dereference in remove_waiter() on self-deadlock")
Reported-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260701131150.0Ijhq4Dw@linutronix.de
Closes: https://lore.kernel.org/all/20260629020049.2082397-1-michael.bommarito@gmail.com

Author: Sebastian Andrzej Siewior

kernel/futex/requeue.c

@@ -645,12 +645,6 @@ int futex_requeue(u32 __user *uaddr1, unsigned int flags1,
 				continue;
 			}
 
-			/* Self-deadlock: non-top waiter already owns the PI futex. */
-			if (rt_mutex_owner(&pi_state->pi_mutex) == this->task) {
-				ret = -EDEADLK;
-				break;
-			}
-
 			ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
 							this->rt_waiter,
 							this->task);