Re: [PATCH v2 3/8] cxl/mem: Register CXL memX devices

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 9 Feb 2021 16:02:54 -0800
Ben Widawsky <ben.widawsky@intel.com> wrote:

> From: Dan Williams <dan.j.williams@intel.com>
> 
> Create the /sys/bus/cxl hierarchy to enumerate:
> 
> * Memory Devices (per-endpoint control devices)
> 
> * Memory Address Space Devices (platform address ranges with
>   interleaving, performance, and persistence attributes)
> 
> * Memory Regions (active provisioned memory from an address space device
>   that is in use as System RAM or delegated to libnvdimm as Persistent
>   Memory regions).
> 
> For now, only the per-endpoint control devices are registered on the
> 'cxl' bus. However, going forward it will provide a mechanism to
> coordinate cross-device interleave.
> 
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>

One stray header, and a request for a tiny bit of reordering to
make it easier to chase through creation and destruction.

Either way with the header move to earlier patch I'm fine with this one.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
>  Documentation/ABI/testing/sysfs-bus-cxl       |  26 ++
>  .../driver-api/cxl/memory-devices.rst         |  17 +
>  drivers/cxl/Makefile                          |   3 +
>  drivers/cxl/bus.c                             |  29 ++
>  drivers/cxl/cxl.h                             |   4 +
>  drivers/cxl/mem.c                             | 301 +++++++++++++++++-
>  6 files changed, 378 insertions(+), 2 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-cxl
>  create mode 100644 drivers/cxl/bus.c
> 


> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 745f5e0bfce3..b3c56fa6e126 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -3,6 +3,7 @@
>  
>  #ifndef __CXL_H__
>  #define __CXL_H__
> +#include <linux/range.h>

Why is this coming in now? Feels like it should have been in earlier
patch that started using struct range

>  
>  #include <linux/bitfield.h>
>  #include <linux/bitops.h>
> @@ -55,6 +56,7 @@
>  	(FIELD_GET(CXLMDEV_RESET_NEEDED_MASK, status) !=                       \
>  	 CXLMDEV_RESET_NEEDED_NOT)
>  
> +struct cxl_memdev;
>  /**
>   * struct cxl_mem - A CXL memory device
>   * @pdev: The PCI device associated with this CXL device.
> @@ -72,6 +74,7 @@
>  struct cxl_mem {
>  	struct pci_dev *pdev;
>  	void __iomem *regs;
> +	struct cxl_memdev *cxlmd;
>  
>  	void __iomem *status_regs;
>  	void __iomem *mbox_regs;
> @@ -90,4 +93,5 @@ struct cxl_mem {
>  	} ram;
>  };
>  
> +extern struct bus_type cxl_bus_type;
>  #endif /* __CXL_H__ */
> diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> index 0a868a15badc..8bbd2495e237 100644
> --- a/drivers/cxl/mem.c
> +++ b/drivers/cxl/mem.c
> @@ -1,11 +1,36 @@
>

> +
> +static void cxl_memdev_release(struct device *dev)
> +{
> +	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
> +
> +	percpu_ref_exit(&cxlmd->ops_active);
> +	ida_free(&cxl_memdev_ida, cxlmd->id);
> +	kfree(cxlmd);
> +}
> +
...

> +static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
> +{
> +	struct pci_dev *pdev = cxlm->pdev;
> +	struct cxl_memdev *cxlmd;
> +	struct device *dev;
> +	struct cdev *cdev;
> +	int rc;
> +
> +	cxlmd = kzalloc(sizeof(*cxlmd), GFP_KERNEL);
> +	if (!cxlmd)
> +		return -ENOMEM;
> +	init_completion(&cxlmd->ops_dead);
> +
> +	/*
> +	 * @cxlm is deallocated when the driver unbinds so operations
> +	 * that are using it need to hold a live reference.
> +	 */
> +	cxlmd->cxlm = cxlm;
> +	rc = percpu_ref_init(&cxlmd->ops_active, cxlmdev_ops_active_release, 0,
> +			     GFP_KERNEL);
> +	if (rc)
> +		goto err_ref;
> +
> +	rc = ida_alloc_range(&cxl_memdev_ida, 0, CXL_MEM_MAX_DEVS, GFP_KERNEL);
> +	if (rc < 0)
> +		goto err_id;
> +	cxlmd->id = rc;
> +
> +	dev = &cxlmd->dev;
> +	device_initialize(dev);
> +	dev->parent = &pdev->dev;
> +	dev->bus = &cxl_bus_type;
> +	dev->devt = MKDEV(cxl_mem_major, cxlmd->id);
> +	dev->type = &cxl_memdev_type;
> +	dev_set_name(dev, "mem%d", cxlmd->id);
> +
> +	cdev = &cxlmd->cdev;
> +	cdev_init(cdev, &cxl_memdev_fops);
> +
> +	rc = cdev_device_add(cdev, dev);
> +	if (rc)
> +		goto err_add;
> +
> +	return devm_add_action_or_reset(dev->parent, cxlmdev_unregister, cxlmd);

This had me scratching my head. The cxlmdev_unregister() if called normally
or in the _or_reset() results in

	percpu_ref_kill(&cxlmd->ops_active);
	cdev_device_del(&cxlmd->cdev, dev);
	wait_for_completion(&cxlmd->ops_dead);
	cxlmd->cxlm = NULL;
	put_device(dev);
	/* If last ref this will result in */
		percpu_ref_exit(&cxlmd->ops_active);
		ida_free(&cxl_memdev_ida, cxlmd->id);
		kfree(cxlmd);

So it's doing all the correct things but not necessarily
in the obvious order.

For simplicity of review perhaps it's worth reordering probe a bit
to get the ida immediately after the cxlmd alloc and
for the cxlmdev_unregister() perhaps reorder the cdev_device_del()
before the percpu_ref_kill().

Trivial obvious as the ordering has no affect but makes it
easy for reviewers to tick off setup vs tear down parts.

> +
> +err_add:
> +	ida_free(&cxl_memdev_ida, cxlmd->id);
> +err_id:
> +	/*
> +	 * Theoretically userspace could have already entered the fops,
> +	 * so flush ops_active.
> +	 */
> +	percpu_ref_kill(&cxlmd->ops_active);
> +	wait_for_completion(&cxlmd->ops_dead);
> +	percpu_ref_exit(&cxlmd->ops_active);
> +err_ref:
> +	kfree(cxlmd);
> +
> +	return rc;
> +}
> +