Messages in this thread | | | Date | Sat, 8 Jan 2011 13:50:50 -0500 (EST) | From | Mikulas Patocka <> | Subject | Re: kobject_put vs module unload |
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On Sat, 8 Jan 2011, Kay Sievers wrote:
> On Sat, Jan 8, 2011 at 19:01, Mikulas Patocka <mpatocka@redhat.com> wrote: > > On Sat, 8 Jan 2011, Kay Sievers wrote: > >> On Sat, Jan 8, 2011 at 14:19, Mikulas Patocka <mpatocka@redhat.com> 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?
Mikulas
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