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Holger Hans Peter Freyther holger at freyther.deHi,
I was discussing this crash[1] with Jan at the 29C3 and recently in
Iceland. On top of that Katarina pointed me to the best practises[2]
of talloc. In general I disagree with them[3] but they provide a nice
solution for the SGSN/MSGB ownership issue.
Methods that send a msgb should create a new local context and attach
it to a global context for all local contexts (so we see them in the
leak report). This would probably be done with a helper function in
libosmocore.
Once the msgb is created, we will steal it into the local context. Then
we pass it down the rabbit hole. Once it is reaching the write_queue it
is stolen back (or into a write queue context). The initial caller will
free his local context. And now there are three options:
a.) The msgb has made it into the write_queue.
b.) The msgb has been already deleted due to an error
c.) The msgb is still in the local context and will be freed.
Using the talloc_steal and the local context will make sure we do not
leak and do not double free. We can (and should) add a warning to see
under which circumstances the msgb has not been freed.
I think the implementation of this will be about 10-15 lines of code
(probably too optimistic).
comments?
holger
[1] http://openbsc.osmocom.org/trac/ticket/55
[2] http://talloc.samba.org/talloc/doc/html/libtalloc__bestpractices.html
[3] Most of our functions only allocate one object. There is no point
in having a hierachy of ROOT -> SingleObject. This indirection is
wasteful in most cases.