[PATCH v2 1/2] nvme: switch to RCU freeing the namespace

[keith.busch@intel.com (Keith Busch)]

On Thu, May 19, 2016@04:48:29PM -0400, Keith Busch wrote:
> On Wed, May 18, 2016@10:52:26PM -0700, Ming Lin wrote:
> > I have not found the root cause yet.
> > Below patch makes reset not occur during active scan work.
> > And I didn't see the crash any more with this patch.
> > 
> > So it seems there is a race somewhere between reset work and scan work.

I haven't been able to reproduce the same failure you're getting. What I
see is namespaces being validated fail because the user interrupted the
process by disabling the controller in the middle of discovery. That's
not good either.

We can't just fence off resets during discovery since we need to let
recovery occur if a controller fails.

There's no good reason to let a user interrupt the process, though.

How about for user initiated resets, we synchronize with the scan
work and set a controller state that allows resets but not scan:

---
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 1a51584..f7e15df 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1209,6 +1209,13 @@ out_unlock:
 	return ret;
 }
 
+static int nvme_reset_ctrl(struct nvme_ctrl *ctrl)
+{
+	ctrl->state = NVME_CTRL_NEW;
+	flush_work(&ctrl->scan_work);
+	return ctrl->ops->reset_ctrl(ctrl);
+}
+
 static long nvme_dev_ioctl(struct file *file, unsigned int cmd,
 		unsigned long arg)
 {
@@ -1222,7 +1229,7 @@ static long nvme_dev_ioctl(struct file *file, unsigned int cmd,
 		return nvme_dev_user_cmd(ctrl, argp);
 	case NVME_IOCTL_RESET:
 		dev_warn(ctrl->device, "resetting controller\n");
-		return ctrl->ops->reset_ctrl(ctrl);
+		return nvme_reset_ctrl(ctrl);
 	case NVME_IOCTL_SUBSYS_RESET:
 		return nvme_reset_subsystem(ctrl);
 	case NVME_IOCTL_RESCAN:
@@ -1248,7 +1255,7 @@ static ssize_t nvme_sysfs_reset(struct device *dev,
 	struct nvme_ctrl *ctrl = dev_get_drvdata(dev);
 	int ret;
 
-	ret = ctrl->ops->reset_ctrl(ctrl);
+	ret = nvme_reset_ctrl(ctrl);
 	if (ret < 0)
 		return ret;
 	return count;
--