[PATCH RT 16/22] crypto: cryptd - add a lock instead preempt_disable/local_bh_disable

[Steven Rostedt]

4.14.63-rt41-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bige...@linutronix.de>

[ Upstream commit 21aedb30d85979697f79a72a084e5d781e323663 ]

cryptd has a per-CPU lock which protected with local_bh_disable() and
preempt_disable().
Add an explicit spin_lock to make the locking context more obvious and
visible to lockdep. Since it is a per-CPU lock, there should be no lock
contention on the actual spinlock.
There is a small race-window where we could be migrated to another CPU
after the cpu_queue has been obtain. This is not a problem because the
actual ressource is protected by the spinlock.

Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
---
 crypto/cryptd.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/crypto/cryptd.c b/crypto/cryptd.c
index 248f6ba41688..54b7985c8caa 100644
--- a/crypto/cryptd.c
+++ b/crypto/cryptd.c
@@ -37,6 +37,7 @@
 struct cryptd_cpu_queue {
        struct crypto_queue queue;
        struct work_struct work;
+       spinlock_t qlock;
 };
 
 struct cryptd_queue {
@@ -115,6 +116,7 @@ static int cryptd_init_queue(struct cryptd_queue *queue,
                cpu_queue = per_cpu_ptr(queue->cpu_queue, cpu);
                crypto_init_queue(&cpu_queue->queue, max_cpu_qlen);
                INIT_WORK(&cpu_queue->work, cryptd_queue_worker);
+               spin_lock_init(&cpu_queue->qlock);
        }
        return 0;
 }
@@ -139,8 +141,10 @@ static int cryptd_enqueue_request(struct cryptd_queue 
*queue,
        atomic_t *refcnt;
        bool may_backlog;
 
-       cpu = get_cpu();
-       cpu_queue = this_cpu_ptr(queue->cpu_queue);
+       cpu_queue = raw_cpu_ptr(queue->cpu_queue);
+       spin_lock_bh(&cpu_queue->qlock);
+       cpu = smp_processor_id();
+
        err = crypto_enqueue_request(&cpu_queue->queue, request);
 
        refcnt = crypto_tfm_ctx(request->tfm);
@@ -157,7 +161,7 @@ static int cryptd_enqueue_request(struct cryptd_queue 
*queue,
        atomic_inc(refcnt);
 
 out_put_cpu:
-       put_cpu();
+       spin_unlock_bh(&cpu_queue->qlock);
 
        return err;
 }
@@ -173,16 +177,11 @@ static void cryptd_queue_worker(struct work_struct *work)
        cpu_queue = container_of(work, struct cryptd_cpu_queue, work);
        /*
         * Only handle one request at a time to avoid hogging crypto workqueue.
-        * preempt_disable/enable is used to prevent being preempted by
-        * cryptd_enqueue_request(). local_bh_disable/enable is used to prevent
-        * cryptd_enqueue_request() being accessed from software interrupts.
         */
-       local_bh_disable();
-       preempt_disable();
+       spin_lock_bh(&cpu_queue->qlock);
        backlog = crypto_get_backlog(&cpu_queue->queue);
        req = crypto_dequeue_request(&cpu_queue->queue);
-       preempt_enable();
-       local_bh_enable();
+       spin_unlock_bh(&cpu_queue->qlock);
 
        if (!req)
                return;
-- 
2.18.0