On Sat, Jan 08, 2011 at 01:50:50PM -0500, Mikulas Patocka wrote: > > > On Sat, 8 Jan 2011, Kay Sievers wrote: > > > On Sat, Jan 8, 2011 at 19:01, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > On Sat, 8 Jan 2011, Kay Sievers wrote: > > >> On Sat, Jan 8, 2011 at 14:19, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > >> > On Fri, 7 Jan 2011, Greg KH wrote: > > >> > > >> >> > 4) the reference obtained at point 1) is dropped, kobject reference count > > >> >> > reaches zero and the release callback is called. But that callback points > > >> >> > to an unloaded module and causes a crash. > > >> >> > > > >> >> > How is it solved? Am I missing something? > > >> >> > > >> >> You have the code that creates and frees the object, to not be in the > > >> >> module that could have been unloaded. It's really just that simple. > > >> > > > >> > If the whole device mapper subsystem can be a module, where can I put the > > >> > code? > > >> > > > >> > I think a similar bug exists in md, it can also be unloaded as a module > > >> > and it has "release" method in its module code. > > >> > > >> If you still have data structures hanging around, these structures are > > >> supposed to take a reference on the module -- and you can not unload > > >> the module as long as this is the case. > > >> > > >> Kay > > > > > > kobject references don't increase module reference count. If kobject held > > > module references, it would be a fix for this bug, but could cause other > > > bugs (some modules could be unloadable due to self-references to its own > > > kobjects). > > > > Sure, they don't automatically take references. It's the job of the > > driver/module, to make sure to pin the module for any data of it, > > which might be still in use. > > > > Kay > > A module can't unpin itself. If it does, the module can be unloaded > immediatelly after module_put(THIS_MODULE) call and the function that > called module_put crashes. > > A module must be unpinned by someone else. The question is: who unpins the > module when kobject references are gone? Who ever you decide to have unpin it. Seriously, it's up to you to handle this properly, it's not something built into the kobject/driver model at all due to it being something that can be done in a number of different ways. thanks, greg k-h -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
