Re: [PATCH v4 2/3] dax/bus: Introduce guard(device) for device_{lock,unlock} flows

From: Jonathan Cameron
Date: Wed Dec 13 2023 - 12:05:21 EST

On Tue, 12 Dec 2023 12:08:31 -0700
Vishal Verma <vishal.l.verma@xxxxxxxxx> wrote:

> Introduce a guard(device) macro to lock a 'struct device', and unlock it
> automatically when going out of scope using Scope Based Resource
> Management semantics. A lot of the sysfs attribute writes in
> drivers/dax/bus.c benefit from a cleanup using these, so change these
> where applicable.
>
> Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
> Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Hi Vishal,

I'm a big fan of this cleanup.h stuff so very happen to see this getting used here.
There are added opportunities for cleanup that result.

Note that almost every time I see people using this stuff they don't look again
at the code post the change so miss the wider cleanup that it enables. So you are
in good company ;)

Jonathan

> ---
> include/linux/device.h | 2 +
> drivers/dax/bus.c | 109 +++++++++++++++++++------------------------------
> 2 files changed, 44 insertions(+), 67 deletions(-)
>
> diff --git a/include/linux/device.h b/include/linux/device.h
> index d7a72a8749ea..a83efd9ae949 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1131,6 +1131,8 @@ void set_secondary_fwnode(struct device *dev, struct fwnode_handle *fwnode);
> void device_set_of_node_from_dev(struct device *dev, const struct device *dev2);
> void device_set_node(struct device *dev, struct fwnode_handle *fwnode);
>
> +DEFINE_GUARD(device, struct device *, device_lock(_T), device_unlock(_T))

Nice. I'd expect this to be widely adopted, so maybe to make things less painful
for backporting changes that depend on it, make this a separate trivial patch
rather than having this in here.

> +
> static inline int dev_num_vf(struct device *dev)
> {
> if (dev->bus && dev->bus->num_vf)
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..ce1356ac6dc2 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -296,9 +296,8 @@ static ssize_t available_size_show(struct device *dev,
> struct dax_region *dax_region = dev_get_drvdata(dev);
> unsigned long long size;
>
> - device_lock(dev);
> + guard(device)(dev);
> size = dax_region_avail_size(dax_region);
> - device_unlock(dev);
>
> return sprintf(buf, "%llu\n", size);
return sprintf(buf, @%llu\n@, dax_region_avail_size(dax_region));
and drop the local variable that adds little perhaps?

> }
> @@ -314,10 +313,9 @@ static ssize_t seed_show(struct device *dev,
> if (is_static(dax_region))
> return -EINVAL;
>
> - device_lock(dev);
> + guard(device)(dev);
> seed = dax_region->seed;
> rc = sprintf(buf, "%s\n", seed ? dev_name(seed) : "");

return sprintf();

> - device_unlock(dev);
>
> return rc;
> }
> @@ -333,10 +331,9 @@ static ssize_t create_show(struct device *dev,
> if (is_static(dax_region))
> return -EINVAL;
>
> - device_lock(dev);
> + guard(device)(dev);
> youngest = dax_region->youngest;
> rc = sprintf(buf, "%s\n", youngest ? dev_name(youngest) : "");

return sprintf();

> - device_unlock(dev);
>
> return rc;
> }
> @@ -345,7 +342,14 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr,
> const char *buf, size_t len)
> {
> struct dax_region *dax_region = dev_get_drvdata(dev);
> + struct dev_dax_data data = {
> + .dax_region = dax_region,
> + .size = 0,
> + .id = -1,
> + .memmap_on_memory = false,
> + };
> unsigned long long avail;
> + struct dev_dax *dev_dax;
> ssize_t rc;
> int val;
>
> @@ -358,38 +362,26 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr,
> if (val != 1)
> return -EINVAL;
>
> - device_lock(dev);
> + guard(device)(dev);
> avail = dax_region_avail_size(dax_region);
> if (avail == 0)
> - rc = -ENOSPC;
> - else {
> - struct dev_dax_data data = {
> - .dax_region = dax_region,
> - .size = 0,
> - .id = -1,
> - .memmap_on_memory = false,
> - };
> - struct dev_dax *dev_dax = devm_create_dev_dax(&data);
> + return -ENOSPC;
>
> - if (IS_ERR(dev_dax))
> - rc = PTR_ERR(dev_dax);
> - else {
> - /*
> - * In support of crafting multiple new devices
> - * simultaneously multiple seeds can be created,
> - * but only the first one that has not been
> - * successfully bound is tracked as the region
> - * seed.
> - */
> - if (!dax_region->seed)
> - dax_region->seed = &dev_dax->dev;
> - dax_region->youngest = &dev_dax->dev;
> - rc = len;
> - }
> - }
> - device_unlock(dev);
> + dev_dax = devm_create_dev_dax(&data);
> + if (IS_ERR(dev_dax))
> + return PTR_ERR(dev_dax);
>
> - return rc;
> + /*
> + * In support of crafting multiple new devices

rewrap this comment for the new indent.

> + * simultaneously multiple seeds can be created,
> + * but only the first one that has not been
> + * successfully bound is tracked as the region
> + * seed.
> + */
> + if (!dax_region->seed)
> + dax_region->seed = &dev_dax->dev;
> + dax_region->youngest = &dev_dax->dev;

Trivial but blank line here would be a nice to have

> + return len;
> }


...

> @@ -1138,18 +1123,14 @@ static ssize_t mapping_store(struct device *dev, struct device_attribute *attr,
> return rc;
>
> rc = -ENXIO;

Not needed with suggested changes that follow.

> - device_lock(dax_region->dev);
> - if (!dax_region->dev->driver) {
> - device_unlock(dax_region->dev);
> + guard(device)(dax_region->dev);
> + if (!dax_region->dev->driver)
> return rc;
return -ENXIO;
> - }
> - device_lock(dev);
>
> + guard(device)(dev);
> to_alloc = range_len(&r);
> if (alloc_is_aligned(dev_dax, to_alloc))
> rc = alloc_dev_dax_range(dev_dax, r.start, to_alloc);
Flip logic here and I'd drop the ternary stuff as well - same in other
similar cases in this patch (though that is just personal taste)

if (!alloc_is_aligned(dev_dax, to_allco))
return -ENXIO.

rc = alloc_dev_dax_range(dev_dax, r.start, to_allco)
if (rc)
return rc;

return len;

> - device_unlock(dev);
> - device_unlock(dax_region->dev);
>
> return rc == 0 ? len : rc;
> }

>