> -----Original Message----- > From: Christoph Hellwig [mailto:h...@lst.de] > Sent: Friday, October 20, 2017 9:49 AM > To: Limonciello, Mario <mario_limoncie...@dell.com> > Cc: g...@kroah.com; dvh...@infradead.org; andy.shevche...@gmail.com; linux- > ker...@vger.kernel.org; platform-driver-...@vger.kernel.org; l...@kernel.org; > quasi...@google.com; pali.ro...@gmail.com; r...@rjwysocki.net; > mj...@google.com; h...@lst.de; gno...@lxorguk.ukuu.org.uk > Subject: Re: [PATCH v10 13/15] platform/x86: wmi: create userspace interface > for > drivers > > On Fri, Oct 20, 2017 at 01:54:36PM +0000, mario.limoncie...@dell.com wrote: > > > -----Original Message----- > > > From: Greg KH [mailto:g...@kroah.com] > > > Sent: Friday, October 20, 2017 8:22 AM > > > To: Limonciello, Mario <mario_limoncie...@dell.com> > > > Cc: dvh...@infradead.org; Andy Shevchenko <andy.shevche...@gmail.com>; > > > LKML <linux-kernel@vger.kernel.org>; platform-driver-...@vger.kernel.org; > Andy > > > Lutomirski <l...@kernel.org>; quasi...@google.com; pali.ro...@gmail.com; > > > r...@rjwysocki.net; mj...@google.com; h...@lst.de; Alan Cox > > > <gno...@lxorguk.ukuu.org.uk> > > > Subject: Re: [PATCH v10 13/15] platform/x86: wmi: create userspace > > > interface > for > > > drivers > > > > > > On Thu, Oct 19, 2017 at 12:50:16PM -0500, Mario Limonciello wrote: > > > > + wblock = container_of(wdev, struct wmi_block, dev); > > > > + if (!wblock) > > > > + return -ENODEV; > > > > > > How can container_of() ever return NULL? If so, you have a very odd > > > memory layout... > > > > > > > I'm assuming this is from set_required_buffer_size right? > > > > The symbol is exported out for other drivers to use. It's possible for > > another > > driver to allocate a wmi_device structure that's not part of a wblock. > > container_of can never return NULL, it does arithmetics on a pointer > based on the type it is embedded into. > > You better don't register a wmi_device that's not part of the block > with your driver. Which others drivers are those, btw?
No drivers do this today, it's obviously not a good idea. I was just saying it's hypothetical. I see that the other methods exported (wmi_evaluate_method and such) to drivers require that it's part of a wblock, so this seems like a reasonable expectation from other drivers. I'll remove this invalid check. > > This one it's possible that a driver isn't bound to a device, and when > > that happens wdriver is NULL. > See above, no it can't. Maybe wblock->dev.dev.driver can be NULL, > but in that case you must not call container_of on it. > container_of() is just pointer math. If you pass in NULL, you will get > a non-NULL value (incremented or decremented). If you pass in a very > tiny number, you might get NULL, but that's still really wrong. > > In other words, these tests will _NEVER_ fail. Go ahead, try it :) I was seeing failures (with NULL) when I tested with some drivers unbound, but I now understand my check is definitely wrong. I'll adjust the check and make sure it's valid. Thank you both for your feedback here.
