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

[Bjorn Helgaas <helgaas@kernel.org>]

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);
 
 static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
 			    const char *buf, size_t count)
@@ -501,7 +502,8 @@ static ssize_t bus_rescan_store(struct device *dev,
 	}
 	return count;
 }
-static DEVICE_ATTR_WO(bus_rescan);
+static struct device_attribute dev_attr_bus_rescan = __ATTR(rescan, 0200, NULL,
+							    bus_rescan_store);
 
 #if defined(CONFIG_PM) && defined(CONFIG_ACPI)
 static ssize_t d3cold_allowed_store(struct device *dev,