On Thu, 2018-07-26 at 18:58 +0200, Sebastian Andrzej Siewior wrote:
> On 2018-07-11 17:19:59 [+0200], Mike Galbraith wrote:
> > Note: patch is the result of code inspection...
> >
> > cryptod disables preemption to provide request enqueue/dequeue exclusion,
> > use a LOCAL_IRQ_LOCK to do the same for RT, keeping preemption enabled.
>
> What about this:
Looks fine to me, I'll ask my arm-thing box for its opinion.
> -------- >8
>
> From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Date: Thu, 26 Jul 2018 18:52:00 +0200
> Subject: [PATCH] crypto: cryptd - add a lock instead
> preempt_disable/local_bh_disable
>
> 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@xxxxxxxxxxxxx>
> ---
> crypto/cryptd.c | 19 +++++++++----------
> 1 file changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/crypto/cryptd.c b/crypto/cryptd.c
> index addca7bae33f..8ad657cddc0a 100644
> --- a/crypto/cryptd.c
> +++ b/crypto/cryptd.c
> @@ -39,6 +39,7 @@ MODULE_PARM_DESC(cryptd_max_cpu_qlen, "Set cryptd Max queue depth");
> struct cryptd_cpu_queue {
> struct crypto_queue queue;
> struct work_struct work;
> + spinlock_t qlock;
> };
>
> struct cryptd_queue {
> @@ -117,6 +118,7 @@ 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);
> }
> pr_info("cryptd: max_cpu_qlen set to %d\n", max_cpu_qlen);
> return 0;
> @@ -141,8 +143,10 @@ static int cryptd_enqueue_request(struct cryptd_queue *queue,
> struct cryptd_cpu_queue *cpu_queue;
> atomic_t *refcnt;
>
> - 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);
> @@ -158,7 +162,7 @@ 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;
> }
> @@ -174,16 +178,11 @@ 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;
--
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