Re: [PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it on dev_dbg

Hi Colin,

On Tue, Sep 1, 2015 at 12:38 PM, Colin Ian King
[off-list ref] wrote:

On 01/09/15 11:35, Geert Uytterhoeven wrote:

quoted

On Tue, Sep 1, 2015 at 12:21 PM, Colin King [off-list ref] wrote:

quoted

On the unlikely event that drv is null, the current code will
perform a null pointer dereference with it when printing a dev_dbg
message.  Instead, the BUG_ON check on drv should be performed
before we emit the dev_dbg message.

What about just removing the BUG_ON()?

The system will crash anyway, providing a backtrace.

I personally think a BUG_ON() shows intention to try to catch an
unexpected issue in a standard way as opposed to just removing it and
then hitting an issue with a null ptr deference.

I think this BUG_ON() was purely used during development of the ps3_vuart
framework.

Note that the corresponding platform_drv_probe() also just dereferences its
driver pointer.

quoted

quoted

Signed-off-by: Colin Ian King <redacted>
---
 drivers/ps3/ps3-vuart.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/ps3/ps3-vuart.c b/drivers/ps3/ps3-vuart.c
index d6db822..632701a 100644
--- a/drivers/ps3/ps3-vuart.c
+++ b/drivers/ps3/ps3-vuart.c

@@ -1000,12 +1000,11 @@ static int ps3_vuart_probe(struct ps3_system_bus_device *dev)
        dev_dbg(&dev->core, "%s:%d\n", __func__, __LINE__);

        drv = ps3_system_bus_dev_to_vuart_drv(dev);
+       BUG_ON(!drv);

        dev_dbg(&dev->core, "%s:%d: (%s)\n", __func__, __LINE__,
                drv->core.core.name);

-       BUG_ON(!drv);
-
        if (dev->port_number >= PORT_COUNT) {
                BUG();
                return -EINVAL;

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