NVMe: Add pci suspend/resume driver callbacks

Hi Dan,

Does it? Let's follow this through:

static void put_nvmeq(struct nvme_queue *nvmeq) __releases(RCU) {
rcu_read_unlock(); put_cpu_var(nvmeq->dev->io_queue);
}

This will use 'NULL' in put_cpu_var, and here's that macro:

#define put_cpu_var(var) do { \
(void)&(var); \
preempt_enable(); \
} while (0)

That's a no-op, right? It is on my config, so it appears to be safe (for now). I'd agree it's not a good idea relying on that macro to never use this parameter, though.

Maybe do this instead:

@@ -282,6 +282,12 @@ static struct nvme_queue *get_nvmeq(struct nvme_dev *dev) __acquires(RCU)
return rcu_dereference(dev->queues[queue_id]);
}

+static void put_nvmeq(struct nvme_dev *dev) __releases(RCU)
+{
+ rcu_read_unlock();
+ put_cpu_var(dev->io_queue);
+}
+
static void put_nvmeq(struct nvme_queue *nvmeq) __releases(RCU)
{
rcu_read_unlock();
@@ -801,7 +807,7 @@ static void nvme_make_request(struct request_queue *q, struct bio *bio)
int result = -EBUSY;

if (!nvmeq) {
- put_nvmeq(NULL);
+ put_ioqueue(ns->dev);
bio_endio(bio, -EIO);
return;
}

Interesting. You're right it's not a problem to pass the NULL pointer here.

regards,
dan carpenter

Wait, no, your explanation is wrong. It's a macro, so it gets expanded by the preprocessor before it gets to the compiler. Like this:

static void put_nvmeq(struct nvme_queue *nvmeq) __releases(RCU)

{
	rcu_read_unlock();
	do {
		(void)&(nvmeq->dev->io_queue);
		preempt_enable();
	} while (0);
}

but it's never evaluated, so the fact that it *would* be a NULL pointer dereference is irrelevant.

Taking a step back, the API is kind of bogus. You shouldn't have to 'put' something that was NULL. So something like this, perhaps?

I wouldn't mind seeing lock_nvmeq() having the same semantics, but that's a larger patch.

index cd8a8bc7..0691e86 100644
@@ -275,29 +275,34 @@ static struct nvme_queue *raw_nvmeq(struct nvme_dev *dev, int qid)
 	return rcu_dereference_raw(dev->queues[qid]);
 }
 
-static struct nvme_queue *get_nvmeq(struct nvme_dev *dev) __acquires(RCU)
+static struct nvme_queue *lock_nvmeq(struct nvme_dev *dev, int q_idx)
+							__acquires(RCU)
 {
-	unsigned queue_id = get_cpu_var(*dev->io_queue);
 	rcu_read_lock();
-	return rcu_dereference(dev->queues[queue_id]);
+	return rcu_dereference(dev->queues[q_idx]);
 }
 
-static void put_nvmeq(struct nvme_queue *nvmeq) __releases(RCU)
+static void unlock_nvmeq(struct nvme_queue *nvmeq) __releases(RCU)
 {
 	rcu_read_unlock();
-	put_cpu_var(nvmeq->dev->io_queue);
 }
 
-static struct nvme_queue *lock_nvmeq(struct nvme_dev *dev, int q_idx)
-							__acquires(RCU)
+static struct nvme_queue *get_nvmeq(struct nvme_dev *dev) __acquires(RCU)
 {
-	rcu_read_lock();
-	return rcu_dereference(dev->queues[q_idx]);
+	struct nvme_queue *nvmeq;
+	unsigned queue_id = get_cpu_var(*dev->io_queue);
+	nvmeq = lock_nvmeq(dev, queue_id);
+	if (nvmeq)
+		return nvmeq;
+	unlock_nvmeq(nvmeq);
+	put_cpu_var(*dev->io_queue);
+	return NULL;
 }
 
-static void unlock_nvmeq(struct nvme_queue *nvmeq) __releases(RCU)
+static void put_nvmeq(struct nvme_queue *nvmeq) __releases(RCU)
 {
-	rcu_read_unlock();
+	unlock_nvmeq(nvmeq);
+	put_cpu_var(nvmeq->dev->io_queue);
 }
 
 /**

@@ -801,7 +806,6 @@ static void nvme_make_request(struct request_queue *q, struct bio *bio)
 	int result = -EBUSY;
 
 	if (!nvmeq) {
-		put_nvmeq(NULL);
 		bio_endio(bio, -EIO);
 		return;
 	}