PCI/sysfs: Fix 'resource_alignment' newline issues

The value of the "resource_alignment" can be specified using a kernel
command-line argument ("pci=resource_alignment=") or through the
corresponding sysfs attribute under the /sys/bus/pci path.

Previously, when the value was set via the kernel command-line argument,
and then subsequently accessed through sysfs attribute, the value read back
was not correct:

  # grep -oE 'pci=resource_alignment.+' /proc/cmdline
  pci=resource_alignment=20@00:1f.2
  # cat /sys/bus/pci/resource_alignment
  20@00:1f.

This was also true when the value was set through the sysfs attribute
without including a trailing newline:

  # echo -n 20@00:1f.2 > /sys/bus/pci/resource_alignment
  # cat /sys/bus/pci/resource_alignment
  20@00:1f.

When it was set through the sysfs attribute *including* a newline,
reading it back worked as intended:

  # echo 20@00:1f.2 > /sys/bus/pci/resource_alignment
  # cat /sys/bus/pci/resource_alignment
  20@00:1f.2

To fix this inconsistency, append a trailing newline in the show() function
and strip the trailing line in the store() function if one is present.

Also, allow for the value previously set using either a command-line
argument or through the sysfs object to be cleared at run-time.

[bhelgaas: fold in kfree fix from
https://lore.kernel.org/linux-pci/20210604133230.983956-4-kw@linux.com]
Fixes: e499081da1a2 ("PCI: Force trailing new line to resource_alignment_param in sysfs")
Link: https://lore.kernel.org/r/20210603000112.703037-4-kw@linux.com
Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 5ed316e..68f57d8 100644 (file)
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -6439,34 +6439,40 @@ static ssize_t resource_alignment_show(struct bus_type *bus, char *buf)
 
        spin_lock(&resource_alignment_lock);
        if (resource_alignment_param)
-               count = sysfs_emit(buf, "%s", resource_alignment_param);
+               count = sysfs_emit(buf, "%s\n", resource_alignment_param);
        spin_unlock(&resource_alignment_lock);
 
-       /*
-        * When set by the command line, resource_alignment_param will not
-        * have a trailing line feed, which is ugly. So conditionally add
-        * it here.
-        */
-       if (count >= 2 && buf[count - 2] != '\n' && count < PAGE_SIZE - 1) {
-               buf[count - 1] = '\n';
-               buf[count++] = 0;
-       }
-
        return count;
 }
 
 static ssize_t resource_alignment_store(struct bus_type *bus,
                                        const char *buf, size_t count)
 {
-       char *param = kstrndup(buf, count, GFP_KERNEL);
+       char *param, *old, *end;
+
+       if (count >= (PAGE_SIZE - 1))
+               return -EINVAL;
 
+       param = kstrndup(buf, count, GFP_KERNEL);
        if (!param)
                return -ENOMEM;
 
+       end = strchr(param, '\n');
+       if (end)
+               *end = '\0';
+
        spin_lock(&resource_alignment_lock);
-       kfree(resource_alignment_param);
-       resource_alignment_param = param;
+       old = resource_alignment_param;
+       if (strlen(param)) {
+               resource_alignment_param = param;
+       } else {
+               kfree(param);
+               resource_alignment_param = NULL;
+       }
        spin_unlock(&resource_alignment_lock);
+
+       kfree(old);
+
        return count;
 }