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Subject[PATCH v2 2/8] locking/rwsem: Enforce queueing when HANDOFF
Date
From: Peter Zijlstra <peterz@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(+)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index e589f69793df..4b9e492abd59 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -468,7 +468,12 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
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 *sem)

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;

--
2.31.1
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