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

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Date:   Thu, 23 Feb 2023 13:26:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     longman@...hat.com, mingo@...hat.com, will@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        boqun.feng@...il.com
Subject: [PATCH 2/6] locking/rwsem: Enforce queueing when HANDOFF

Ensure that HANDOFF disables all spinning and stealing.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.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;