On Fri, Oct 19, 2012 at 10:36:39AM -0700, Dmitry Torokhov wrote: > On Fri, Oct 19, 2012 at 06:09:51PM +0100, Al Viro wrote: > > On Fri, Oct 19, 2012 at 09:33:18AM -0700, Dmitry Torokhov wrote: > > > > > We are now removing instance of character device corresponding to input > > > device when input device disappears. > > > > > > Ah, I know... cdev is embedded in evdev, but lives longer.. I do want to > > > keep cdev embedded as it allows me to easily get to evdev in > > > evdev_open(), but I need to be able to add and then drop reference to > > > evdev from cdev's ->release() method. This means I need to override it. > > > > > > Or I could have cdev separately allocated, but then I'd like to have a > > > void pointer in "struct cdev" so I could get from it back to > > > corresponding evdev. > > > > Your real problem is that you have two kobjects embedded into the same > > thing. It can work, but you need to make the secondary (one that does > > *not* free in its ->release()) pin the primary. Sigh... Device model > > sucks, film at 11... > > Right, but "cdev" is currently "sealed": it does not allow specifying a > custom release function from which I could unpin primary (evdev). You > are the author/owner of cdev code, so that is why I was asking for > your opinion as to what is the best way to proceed: > > 1. Allocate cdev separately and add void * to struct cdev so that it is > easy to get to corresponding structure on evdev_open. > > 2. Keep cdev embedded in evdev but export cdev's cleanup method and > have evdev override ->release with its own version that calls > cdev_default_release() and then unpins evdev stucture. > > 3. Add struct device *parent to struct cdev and have it pin and unpin it > for us (if it is set up).
The last one would be my preference, TBH, but I'm not sure how to do it cleanly. The thing is, kobject_del() would have to be done at some point. _Before_ we have dropped the last references. And once we have, we are back to the original race, AFAICS. What's pinning that cdev reference, BTW? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
