Re: [Linux-kernel-mentees] [PATCH v2] PCI: sysfs: Change bus_rescan and dev_rescan to rescan

[Greg KH <greg@kroah.com>]

On Wed, Mar 25, 2020 at 05:10:33PM -0500, Bjorn Helgaas wrote:
> Hi Kelsey,
> 
> On Wed, Mar 25, 2020 at 09:17:08AM -0600, Kelsey Skunberg wrote:
> > From: Kelsey Skunberg <kelsey.skunberg@gmail.com>
> > 
> > rename device attribute name arguments 'bus_rescan' and 'dev_rescan' to 'rescan'
> > to avoid breaking userspace applications.
> > 
> > The attribute argument names were changed in the following commits:
> > 8bdfa145f582 ("PCI: sysfs: Define device attributes with DEVICE_ATTR*()")
> > 4e2b79436e4f ("PCI: sysfs: Change DEVICE_ATTR() to DEVICE_ATTR_WO()")
> > 
> > Revert the names used for attributes back to the names used before the above
> > patches were applied. This also requires to change DEVICE_ATTR_WO() to
> > DEVICE_ATTR() and __ATTR().
> > 
> > Note when using DEVICE_ATTR() the attribute is automatically named
> > dev_attr_<name>.attr. To avoid duplicated names between attributes, use
> > __ATTR() instead of DEVICE_ATTR() to a assign a custom attribute name for
> > dev_rescan.
> > 
> > change bus_rescan_store() to dev_bus_rescan_store() to complete matching the
> > names used before the mentioned patches were applied.
> > 
> > Fixes: 8bdfa145f582 ("PCI: sysfs: Define device attributes with DEVICE_ATTR*()")
> > Fixes: 4e2b79436e4f ("PCI: sysfs: Change DEVICE_ATTR() to DEVICE_ATTR_WO()")
> > 
> > Cc: stable <stable@vger.kernel.org>
> > Signed-off-by: Kelsey Skunberg <kelsey.skunberg@gmail.com>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> > 
> > v2 updates: 
> > 	commit log updated to include 'Fixes: *' and Cc: stable to aid commit
> > 	being backported properly.
> > 
> >  drivers/pci/pci-sysfs.c | 17 ++++++++++-------
> >  1 file changed, 10 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > index 13f766db0684..667e13d597ff 100644
> > --- a/drivers/pci/pci-sysfs.c
> > +++ b/drivers/pci/pci-sysfs.c
> > @@ -464,7 +464,10 @@ static ssize_t dev_rescan_store(struct device *dev,
> >  	}
> >  	return count;
> >  }
> > -static DEVICE_ATTR_WO(dev_rescan);
> > +static struct device_attribute dev_rescan_attr = __ATTR(rescan,
> > +							0220, NULL,
> > +							dev_rescan_store);
> > +
> >  
> >  static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
> >  			    const char *buf, size_t count)
> > @@ -481,9 +484,9 @@ static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
> >  static DEVICE_ATTR_IGNORE_LOCKDEP(remove, 0220, NULL,
> >  				  remove_store);
> >  
> > -static ssize_t bus_rescan_store(struct device *dev,
> > -				struct device_attribute *attr,
> > -				const char *buf, size_t count)
> > +static ssize_t dev_bus_rescan_store(struct device *dev,
> > +				    struct device_attribute *attr,
> > +				    const char *buf, size_t count)
> >  {
> >  	unsigned long val;
> >  	struct pci_bus *bus = to_pci_bus(dev);
> > @@ -501,7 +504,7 @@ static ssize_t bus_rescan_store(struct device *dev,
> >  	}
> >  	return count;
> >  }
> > -static DEVICE_ATTR_WO(bus_rescan);
> > +static DEVICE_ATTR(rescan, 0220, NULL, dev_bus_rescan_store);
> >  
> >  #if defined(CONFIG_PM) && defined(CONFIG_ACPI)
> >  static ssize_t d3cold_allowed_store(struct device *dev,
> > @@ -641,7 +644,7 @@ static struct attribute *pcie_dev_attrs[] = {
> >  };
> >  
> >  static struct attribute *pcibus_attrs[] = {
> > -	&dev_attr_bus_rescan.attr,
> > +	&dev_attr_rescan.attr,
> >  	&dev_attr_cpuaffinity.attr,
> >  	&dev_attr_cpulistaffinity.attr,
> >  	NULL,
> > @@ -1487,7 +1490,7 @@ static umode_t pci_dev_attrs_are_visible(struct kobject *kobj,
> >  
> >  static struct attribute *pci_dev_hp_attrs[] = {
> >  	&dev_attr_remove.attr,
> > -	&dev_attr_dev_rescan.attr,
> > +	&dev_rescan_attr.attr,
> >  	NULL,
> >  };
> 
> Thanks for taking care of this!  Two questions:
> 
> 1) You supplied permissions of 0220, but DEVICE_ATTR_WO()
> uses__ATTR_WO(), which uses 0200.  Shouldn't we keep 0200?
> 
> 2) I think the use of __ATTR() for the device side and DEVICE_ATTR()
> for the bus side is confusing.  Couldn't we accomplish the same thing
> with a patch like the following (compiled but not tested)?
> 
> Bjorn
> 
> 
> commit 06094b3fd9f1 ("PCI: sysfs: Revert "rescan" file renames")
> Author: Kelsey Skunberg <kelsey.skunberg@gmail.com>
> Date:   Wed Mar 25 09:17:08 2020 -0600
> 
>     PCI: sysfs: Revert "rescan" file renames
>     
>     We changed these sysfs filenames:
>     
>       .../pci_bus/<domain:bus>/rescan  ->  .../pci_bus/<domain:bus>/bus_rescan
>       .../<domain:bus:dev.fn>/rescan   ->  .../<domain:bus:dev.fn>/dev_rescan
>     
>     and Ruslan reported [1] that this broke a userspace application.
>     
>     Revert these name changes so both files are named "rescan" again.
>     
>     The argument to DEVICE_ATTR_WO() determines both the struct
>     device_attribute name and the .store() function name.  We have to
>     use __ATTR() so we can specify different .store() functions for
>     the two "rescan" files.
>     
>     [1] https://lore.kernel.org/r/CAB=otbSYozS-ZfxB0nCiNnxcbqxwrHOSYxJJtDKa63KzXbXgpw@mail.gmail.com
>     
>     [bhelgaas: commit log]
>     Fixes: 8bdfa145f582 ("PCI: sysfs: Define device attributes with DEVICE_ATTR*()")
>     Fixes: 4e2b79436e4f ("PCI: sysfs: Change DEVICE_ATTR() to DEVICE_ATTR_WO()")
>     Link: https://lore.kernel.org/r/20200325151708.32612-1-skunberg.kelsey@gmail.com
>     Signed-off-by: Kelsey Skunberg <kelsey.skunberg@gmail.com>
>     Cc: stable@vger.kernel.org	# v5.4+
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 13f766db0684..bf025a2c296d 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -464,7 +464,8 @@ static ssize_t dev_rescan_store(struct device *dev,
>  	}
>  	return count;
>  }
> -static DEVICE_ATTR_WO(dev_rescan);
> +static struct device_attribute dev_attr_dev_rescan = __ATTR(rescan, 0200, NULL,
> +							    dev_rescan_store);

Oops, this should just be DEVICE_ATTR(), no need for __ATTR() as this
isn't a kobject-only file.

So how about:

static DEVICE_ATTR(rescan, 0200, NULL, dev_rescan_store);

Much smaller :)

Sorry I missed that in the original review.

thanks,

greg k-h