[PATCH] IB: allow NULL sa_query callbacks

Check if a client passes a NULL callback into an SA query, and if so, never
call back.  This fixes an oops if someone unloads ib_ipoib and ib_sa in
rapid succession.  ib_ipoib does an MCMember delete with a NULL callback
and 0 timeout on unload, which is usually fine since the delete completes
successfully.  However, if ib_sa is unloaded immediately afterwards, the
delete will be canceled and ib_sa will try to call the (now already
unloaded) ib_ipoib module back with the cancel completion, which triggers
the oops.
Signed-off-by: Roland Dreier <roland@topspin.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/infiniband/core/sa_query.c

@@ -587,7 +587,7 @@ int ib_sa_path_rec_get(struct ib_device *device, u8 port_num,
 
 	init_mad(query->sa_query.mad, agent);
 
-	query->sa_query.callback              = ib_sa_path_rec_callback;
+	query->sa_query.callback              = callback ? ib_sa_path_rec_callback : NULL;
 	query->sa_query.release               = ib_sa_path_rec_release;
 	query->sa_query.port                  = port;
 	query->sa_query.mad->mad_hdr.method   = IB_MGMT_METHOD_GET;
@@ -663,7 +663,7 @@ int ib_sa_mcmember_rec_query(struct ib_device *device, u8 port_num,
 
 	init_mad(query->sa_query.mad, agent);
 
-	query->sa_query.callback              = ib_sa_mcmember_rec_callback;
+	query->sa_query.callback              = callback ? ib_sa_mcmember_rec_callback : NULL;
 	query->sa_query.release               = ib_sa_mcmember_rec_release;
 	query->sa_query.port                  = port;
 	query->sa_query.mad->mad_hdr.method   = method;
@@ -698,6 +698,7 @@ static void send_handler(struct ib_mad_agent *agent,
 	if (!query)
 		return;
 
+	if (query->callback)
 		switch (mad_send_wc->status) {
 		case IB_WC_SUCCESS:
 			/* No callback -- already got recv */
@@ -736,7 +737,7 @@ static void recv_handler(struct ib_mad_agent *mad_agent,
 	query = idr_find(&query_idr, mad_recv_wc->wc->wr_id);
 	spin_unlock_irqrestore(&idr_lock, flags);
 
-	if (query) {
+	if (query && query->callback) {
 		if (mad_recv_wc->wc->status == IB_WC_SUCCESS)
 			query->callback(query,
 					mad_recv_wc->recv_buf.mad->mad_hdr.status ?