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Subject[PATCH RT 16/22] crypto: cryptd - add a lock instead preempt_disable/local_bh_disable
4.14.63-rt41-rc1 stable review patch.
If anyone has any objections, please let me know.

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

From: Sebastian Andrzej Siewior <bigeasy@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 <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@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

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