On Sat, Jan 04, 2014 at 07:42:28PM -0800, Greg Kroah-Hartman wrote: > On Sat, Jan 04, 2014 at 03:35:39PM -0500, Mikulas Patocka wrote: > > > > > > On Sat, 4 Jan 2014, Greg Kroah-Hartman wrote: > > > > > On Sat, Jan 04, 2014 at 01:06:01PM -0500, Mikulas Patocka wrote: > > > > Hi > > > > > > > > I noticed that Jeff Mahoney added a new structure kobj_completion, defined > > > > in include/linux/kobj_completion.h to the kernel 3.13-rc1 in the patch > > > > eee031649707db3c9920d9498f8d03819b74fc23. In the current upstream kernel, > > > > this interface is still unused. > > > > > > There are pending btrfs patches to use this interface. > > > > > > > However, converting the drivers to use kobj_completion is not trivial > > > > (note that all users of the original kobject interface are buggy - so all > > > > of them need to be converted). > > > > > > Wait, what? How are "all users" buggy? Please explain this in detail. > > > > 1) some code takes a reference to a kobject > > 2) the user unloads the device > > 3) the device driver unload routine calls kobject_put (but there is still > > reference, so the kobject is not destroyed) > > A driver should never be messing around with "raw" kobjects, they should > be using a 'struct device' which is created/managed by the subsystem > they belong to. See Dmitry's example of input and serio as ways to do > this, also USB and PCI do this properly. Well, Mikulas is correct in the sense that there is still a race between release function invoking the final module_put() and getting preempted and module getting unloaded by another thread. Hitting this race is pretty hard though. -- Dmitry -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
