diff mbox series

[v2,03/15] auxdisplay: linedisp: Use unique number for id

Message ID 20240212170423.2860895-4-andriy.shevchenko@linux.intel.com
State New
Headers
Series auxdisplay: linedisp: Clean up and add new driver |

Commit Message

Andy Shevchenko Feb. 12, 2024, 5:01 p.m. UTC 
  The absence of decrementation of linedisp_id is incorrect in two ways,
i.e. it may cause:
- an ID exhaustion
- (and if the above is addressed) a duplicate id number may be allocated
  next time a device is added

Replace above mentioned approach by using IDA framework.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/auxdisplay/line-display.c | 13 ++++++++++---
 drivers/auxdisplay/line-display.h |  2 ++
 2 files changed, 12 insertions(+), 3 deletions(-)

Comments

Geert Uytterhoeven Feb. 15, 2024, 10:03 a.m. UTC | #1 
On Mon, Feb 12, 2024 at 6:04 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
> The absence of decrementation of linedisp_id is incorrect in two ways,
> i.e. it may cause:
> - an ID exhaustion
> - (and if the above is addressed) a duplicate id number may be allocated
>   next time a device is added
>
> Replace above mentioned approach by using IDA framework.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>

> --- a/drivers/auxdisplay/line-display.h
> +++ b/drivers/auxdisplay/line-display.h
> @@ -14,6 +14,7 @@
>  /**
>   * struct linedisp - character line display private data structure
>   * @dev: the line display device
> + * @id: instance id of this display
>   * @timer: timer used to implement scrolling
>   * @update: function called to update the display
>   * @buf: pointer to the buffer for the string currently displayed
> @@ -25,6 +26,7 @@
>   */
>  struct linedisp {
>         struct device dev;
> +       unsigned int id;

Note that there is a hole on 64-bit platforms.
Hence I'd move id below, so the hole is at the end of the
structure, and might be filled by future changes.

>         struct timer_list timer;
>         void (*update)(struct linedisp *linedisp);
>         char *buf;

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
Andy Shevchenko Feb. 15, 2024, 11:28 a.m. UTC | #2 
On Thu, Feb 15, 2024 at 11:03:27AM +0100, Geert Uytterhoeven wrote:
> On Mon, Feb 12, 2024 at 6:04 PM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:

..

> >  struct linedisp {
> >         struct device dev;
> > +       unsigned int id;
> 
> Note that there is a hole on 64-bit platforms.
> Hence I'd move id below, so the hole is at the end of the
> structure, and might be filled by future changes.

I had checked timer_list, but while it has holes, without debug it ends on
4-bytes boundary (without debug enabled), otherwise on 8-bytes.
Nevertheless, relying on the above seems fragile, so I follow your suggestion.
Thank you!

> >         struct timer_list timer;
> >         void (*update)(struct linedisp *linedisp);
> >         char *buf;
diff mbox series

Patch

diff --git a/drivers/auxdisplay/line-display.c b/drivers/auxdisplay/line-display.c
index 310e9bfb41ae..c4dbb13293d1 100644
--- a/drivers/auxdisplay/line-display.c
+++ b/drivers/auxdisplay/line-display.c
@@ -11,6 +11,7 @@ 
 #include <generated/utsrelease.h>
 
 #include <linux/device.h>
+#include <linux/idr.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/string.h>
@@ -188,11 +189,14 @@  static struct attribute *linedisp_attrs[] = {
 };
 ATTRIBUTE_GROUPS(linedisp);
 
+static DEFINE_IDA(linedisp_id);
+
 static void linedisp_release(struct device *dev)
 {
 	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
 
 	kfree(linedisp->message);
+	ida_free(&linedisp_id, linedisp->id);
 }
 
 static const struct device_type linedisp_type = {
@@ -214,7 +218,6 @@  int linedisp_register(struct linedisp *linedisp, struct device *parent,
 		      unsigned int num_chars, char *buf,
 		      void (*update)(struct linedisp *linedisp))
 {
-	static atomic_t linedisp_id = ATOMIC_INIT(-1);
 	int err;
 
 	memset(linedisp, 0, sizeof(*linedisp));
@@ -225,9 +228,13 @@  int linedisp_register(struct linedisp *linedisp, struct device *parent,
 	linedisp->num_chars = num_chars;
 	linedisp->scroll_rate = DEFAULT_SCROLL_RATE;
 
+	err = ida_alloc(&linedisp_id, GFP_KERNEL);
+	if (err < 0)
+		return err;
+	linedisp->id = err;
+
 	device_initialize(&linedisp->dev);
-	dev_set_name(&linedisp->dev, "linedisp.%lu",
-		     (unsigned long)atomic_inc_return(&linedisp_id));
+	dev_set_name(&linedisp->dev, "linedisp.%u", linedisp->id);
 
 	/* initialise a timer for scrolling the message */
 	timer_setup(&linedisp->timer, linedisp_scroll, 0);
diff --git a/drivers/auxdisplay/line-display.h b/drivers/auxdisplay/line-display.h
index 0f5891d34c48..1fbe57fdc4cb 100644
--- a/drivers/auxdisplay/line-display.h
+++ b/drivers/auxdisplay/line-display.h
@@ -14,6 +14,7 @@ 
 /**
  * struct linedisp - character line display private data structure
  * @dev: the line display device
+ * @id: instance id of this display
  * @timer: timer used to implement scrolling
  * @update: function called to update the display
  * @buf: pointer to the buffer for the string currently displayed
@@ -25,6 +26,7 @@ 
  */
 struct linedisp {
 	struct device dev;
+	unsigned int id;
 	struct timer_list timer;
 	void (*update)(struct linedisp *linedisp);
 	char *buf;