From: Guillaume Nault <[email protected]> Date: Tue, 12 Mar 2013 11:36:50 +0100
> On Fri, Mar 01, 2013 at 02:12:52PM -0500, David Miller wrote: >> Looking at how this code works, it is such a terrible design. This >> whole reference counting issue exists purely because >> pppol2tp_sock_to_session() grabs the 'sk' reference. >> >> In all but one case, it need not do this. >> >> The socket system calls have an implicit reference to 'sk' via >> socket->sk. If you can get into the system call and socket->sk >> is non-NULL then 'sk' is NOT going anywhere. >> >> And all of these system call handlers have this pattern: >> >> session = pppol2tp_sock_to_session(sk); >> ... >> sock_put(sk); >> >> The only case where the reference count is really needed is that >> sequence in pppol2tp_release(). >> >> Long term the right thing to do here is stop having this session >> grabber function take the 'sk' reference. Then in pppol2tp_release >> we'll grab a reference explicitly. At all the other call sites we >> then blast aweay all of the sock_put(sk) paths. >> > Could this also apply to l2tp_sock_to_tunnel() (in l2tp_core.h)? As per > my understanding, none of its callers needs to take a socket reference. > So sock_hold() could be removed in both pppol2tp_sock_to_session() and > l2tp_sock_to_tunnel() functions. The corresponding sock_put() calls > would then be removed from all calling functions but pppol2tp_release(). > If this is correct, I'll send a patch for net-next. Yes, it could be simplified in this way too. Just make sure that this interface is only used in system call / user context, where we know the underlying socket cannot go away on us. -- 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/
