[PATCH 2/6] locking/rwsem: Enforce queueing when HANDOFF

From: Peter Zijlstra <peterz@infradead.org>
To: longman@redhat.com, mingo@redhat.com, will@kernel.org
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, boqun.feng@gmail.com
Subject: [PATCH 2/6] locking/rwsem: Enforce queueing when HANDOFF
Date: Thu, 23 Feb 2023 13:26:44 +0100	[thread overview]
Message-ID: <20230223123319.428168721@infradead.org> (raw)
In-Reply-To: 20230223122642.491637862@infradead.org

Ensure that HANDOFF disables all spinning and stealing.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/locking/rwsem.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -468,7 +468,12 @@ static void rwsem_mark_wake(struct rw_se
 					adjustment -= RWSEM_FLAG_HANDOFF;
 					lockevent_inc(rwsem_rlock_handoff);
 				}
+				/*
+				 * With HANDOFF set for reader, we must
+				 * terminate all spinning.
+				 */
 				waiter->handoff_set = true;
+				rwsem_set_nonspinnable(sem);
 			}
 
 			atomic_long_add(-adjustment, &sem->count);
@@ -755,6 +760,10 @@ rwsem_spin_on_owner(struct rw_semaphore
 
 	owner = rwsem_owner_flags(sem, &flags);
 	state = rwsem_owner_state(owner, flags);
+
+	if (owner == current)
+		return OWNER_NONSPINNABLE;	/* Handoff granted */
+
 	if (state != OWNER_WRITER)
 		return state;
 


