Re: [PATCH] locking/qspinlock: Fix typo of lock word transition in the uncontended case

From: Waiman Long
Date: Mon Aug 09 2021 - 12:22:47 EST


On 8/9/21 9:40 AM, Will Deacon wrote:
On Thu, Jul 15, 2021 at 11:08:47AM +0800, Zenghui Yu wrote:
If the queue head is the only one in the queue and nobody is concurrently
setting PENDING bit, the uncontended transition should be n,0,0 -> 0,0,1.

Fix the typo.

Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
---
kernel/locking/qspinlock.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index cbff6ba53d56..591835415698 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -355,7 +355,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
* If we observe contention, there is a concurrent locker.
*
* Undo and queue; our setting of PENDING might have made the
- * n,0,0 -> 0,0,0 transition fail and it will now be waiting
+ * n,0,0 -> 0,0,1 transition fail and it will now be waiting
* on @next to become !NULL.
*/
I think this is an important typo fix as you're right that we don't
transition directly from having a waitqueue installed in the tail straight
to an unlocked state.

Acked-by: Will Deacon <will@xxxxxxxxxx>

Then again, I acked the patch introducing this comment so what do I know?

We usually focus more on the actual code than the associated comment. I am not surprise we may miss that. I do agree that the proposed change is better.

Acked-by: Waiman Long <longman@xxxxxxxxxx>