Re: [PATCH v3 1/2] dax/bus: fix mapping attribute error reporting

[Alison Schofield <alison.schofield@intel.com>]

On Thu, Sep 24, 2026 at 10:50:34AM +0800, Muchun Song wrote:
> After the DAX configuration locking was converted to rwsems, successful
> lock acquisition leaves rc set to zero in mapping_store(). Two error
> paths can return this stale value: an unbound region driver and a
> misaligned range size. The sysfs write therefore reports success without
> allocating the requested range.
> 
> Return -ENXIO when the region driver is not bound and -EINVAL when the
> range size is misaligned.

Reviewed-by: Alison Schofield <alison.schofield@intel.com>

Will modify subject line upon applying like so:
dax/bus: Return errors for invalid mapping requests

> 
> Fixes: c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local rwsem")
> Assisted-by: LLM
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> ---
> v3:
> - Collect Reviewed-by from Dave Jiang
> 
> v2:
> - Return explicit errors before Device DAX range allocation
>   (suggested by Dave Jiang)
> - Move the patch before range alignment validation for independent
>   backports (suggested by Dave Jiang)
> ---
>  drivers/dax/bus.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index b809e1a264af..e40c25401cf0 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1192,7 +1192,7 @@ static ssize_t mapping_store(struct device *dev, struct device_attribute *attr,
>  		return rc;
>  	if (!dax_region->dev->driver) {
>  		up_write(&dax_region_rwsem);
> -		return rc;
> +		return -ENXIO;
>  	}
>  	rc = down_write_killable(&dax_dev_rwsem);
>  	if (rc) {
> @@ -1201,8 +1201,12 @@ static ssize_t mapping_store(struct device *dev, struct device_attribute *attr,
>  	}
>  
>  	to_alloc = range_len(&r);
> -	if (alloc_is_aligned(dev_dax, to_alloc))
> +	if (!alloc_is_aligned(dev_dax, to_alloc)) {
> +		dev_dbg(dev, "%s: size: %zu misaligned\n", __func__, to_alloc);
> +		rc = -EINVAL;
> +	} else {
>  		rc = alloc_dev_dax_range(dev_dax, r.start, to_alloc);
> +	}
>  	up_write(&dax_dev_rwsem);
>  	up_write(&dax_region_rwsem);
>  
> -- 
> 2.54.0
>