[tip: core/rcu] rcu/tree: Repeat the monitor if any free channel is busy

[tip-bot2 for Uladzislau Rezki (Sony)]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     594aa5975b9b5cfe9edaec06170e43b8c0607377
Gitweb:        https://git.kernel.org/tip/594aa5975b9b5cfe9edaec06170e43b8c0607377
Author:        Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
AuthorDate:    Mon, 25 May 2020 23:47:47 +02:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 29 Jun 2020 11:59:25 -07:00

rcu/tree: Repeat the monitor if any free channel is busy

It is possible that one of the channels cannot be detached
because its free channel is busy and previously queued data
has not been processed yet. On the other hand, another
channel can be successfully detached causing the monitor
work to stop.

Prevent that by rescheduling the monitor work if there are
any channels in the pending state after a detach attempt.

Fixes: 34c881745549e ("rcu: Support kfree_bulk() interface in kfree_rcu()")
Acked-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/tree.c |  9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e0425fa..5151fe4 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3105,7 +3105,7 @@ static void kfree_rcu_work(struct work_struct *work)
 static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
 {
 	struct kfree_rcu_cpu_work *krwp;
-	bool queued = false;
+	bool repeat = false;
 	int i;
 
 	lockdep_assert_held(&krcp->lock);
@@ -3143,11 +3143,14 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
 			 * been detached following each other, one by one.
 			 */
 			queue_rcu_work(system_wq, &krwp->rcu_work);
-			queued = true;
 		}
+
+		/* Repeat if any "free" corresponding channel is still busy. */
+		if (krcp->bhead || krcp->head)
+			repeat = true;
 	}
 
-	return queued;
+	return !repeat;
 }
 
 static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp,