[PATCH 0/2] driver core: Improve warning backtrace in device probing

[PATCH 0/2] driver core: Improve warning backtrace in device probing

[Geert Uytterhoeven]

	Hi Greg, Rafael,

Once in a while, the WARN_ON() in really_probe() is triggered due to a
bug in a driver or subsystem.  While the backtrace provides some clues,
it does not reveal the offending device.

Hence this patch series adds a new dev_WARN_ON() helper, and uses that.

Thanks!

Geert Uytterhoeven (2):
  driver core: Add dev_WARN_ON() helper
  driver core: Print device in really_probe() warning backtrace

 drivers/base/dd.c      | 2 +-
 include/linux/device.h | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

-- 
2.17.1

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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

[PATCH 1/2] driver core: Add dev_WARN_ON() helper

[Geert Uytterhoeven]

It is quite useful to print the related device in a warning backtrace.
Hence add a "dev_*" variant of WARN_ON() to handle this.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 include/linux/device.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/device.h b/include/linux/device.h
index f05c5b92e61f535a..05089c329620472a 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1902,6 +1902,9 @@ do {									\
 	WARN_ONCE(condition, "%s %s: " format, \
 			dev_driver_string(dev), dev_name(dev), ## arg)
 
+#define dev_WARN_ON(dev, condition) \
+	WARN(condition, "%s %s", dev_driver_string(dev), dev_name(dev))
+
 /* Create alias, so I can be autoloaded. */
 #define MODULE_ALIAS_CHARDEV(major,minor) \
 	MODULE_ALIAS("char-major-" __stringify(major) "-" __stringify(minor))
-- 
2.17.1

[PATCH 2/2] driver core: Print device in really_probe() warning backtrace

[Geert Uytterhoeven]

If a device already has devres items attached before probing, a warning
backtrace is printed.  However, this backtrace does not reveal the
offending device, leaving the user uninformed.

Use dev_WARN_ON() instead of WARN_ON() to fix this.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 drivers/base/dd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index d811e60610d33ae9..a7e8040ef0003f44 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -516,7 +516,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 	atomic_inc(&probe_count);
 	pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
 		 drv->bus->name, __func__, drv->name, dev_name(dev));
-	WARN_ON(!list_empty(&dev->devres_head));
+	dev_WARN_ON(dev, !list_empty(&dev->devres_head));
 
 re_probe:
 	dev->driver = drv;
-- 
2.17.1

Re: [PATCH 2/2] driver core: Print device in really_probe() warning backtrace

[Greg Kroah-Hartman]

On Wed, Nov 20, 2019 at 03:36:19PM +0100, Geert Uytterhoeven wrote:
> If a device already has devres items attached before probing, a warning
> backtrace is printed.  However, this backtrace does not reveal the
> offending device, leaving the user uninformed.
> 
> Use dev_WARN_ON() instead of WARN_ON() to fix this.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
>  drivers/base/dd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index d811e60610d33ae9..a7e8040ef0003f44 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -516,7 +516,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>  	atomic_inc(&probe_count);
>  	pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
>  		 drv->bus->name, __func__, drv->name, dev_name(dev));
> -	WARN_ON(!list_empty(&dev->devres_head));
> +	dev_WARN_ON(dev, !list_empty(&dev->devres_head));

We really do not want WARN_ON() anywhere, as that causes systems with
panic-on-warn to reboot.

If this can happen, we should switch it to a real error message, with
dev_err() and the like, and recover properly.

I don't want to make it easier to add WARN_ON() lines, like
dev_WARN_ON() would allow, instead we should be removing them, as they
encourage slopping programming habits.

thanks,

greg k-h

Re: [PATCH 2/2] driver core: Print device in really_probe() warning backtrace

[Geert Uytterhoeven]

Hi Greg,

On Thu, Nov 21, 2019 at 2:57 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> On Wed, Nov 20, 2019 at 03:36:19PM +0100, Geert Uytterhoeven wrote:
> > If a device already has devres items attached before probing, a warning
> > backtrace is printed.  However, this backtrace does not reveal the
> > offending device, leaving the user uninformed.
> >
> > Use dev_WARN_ON() instead of WARN_ON() to fix this.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

> > --- a/drivers/base/dd.c
> > +++ b/drivers/base/dd.c
> > @@ -516,7 +516,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
> >       atomic_inc(&probe_count);
> >       pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
> >                drv->bus->name, __func__, drv->name, dev_name(dev));
> > -     WARN_ON(!list_empty(&dev->devres_head));
> > +     dev_WARN_ON(dev, !list_empty(&dev->devres_head));
>
> We really do not want WARN_ON() anywhere, as that causes systems with
> panic-on-warn to reboot.
>
> If this can happen, we should switch it to a real error message, with
> dev_err() and the like, and recover properly.

If this happens, there's something serious wrong with resource management,
beyond recovery.

> I don't want to make it easier to add WARN_ON() lines, like
> dev_WARN_ON() would allow, instead we should be removing them, as they
> encourage slopping programming habits.

OK, will respin, using dev_warn().

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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