RDMA/iwcm: Don't access a cm_id after dropping reference

cm_work_handler() can access cm_id_priv after it drops its reference
by calling iwch_deref_id(), which might cause it to be freed.  The fix
is to look at whether IWCM_F_CALLBACK_DESTROY is set _before_ dropping
the reference.  Then if it was set, free the cm_id on this thread.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/infiniband/core/iwcm.c b/drivers/infiniband/core/iwcm.c
index 223b1aa7d92b..81c9195b512a 100644
--- a/drivers/infiniband/core/iwcm.c
+++ b/drivers/infiniband/core/iwcm.c
@@ -839,6 +839,7 @@ static void cm_work_handler(struct work_struct *_work)
         unsigned long flags;
         int empty;
         int ret = 0;
+        int destroy_id;
 
         spin_lock_irqsave(&cm_id_priv->lock, flags);
         empty = list_empty(&cm_id_priv->work_list);
@@ -857,9 +858,9 @@ static void cm_work_handler(struct work_struct *_work)
                         destroy_cm_id(&cm_id_priv->id);
                 }
                 BUG_ON(atomic_read(&cm_id_priv->refcount)==0);
+                destroy_id = test_bit(IWCM_F_CALLBACK_DESTROY, &cm_id_priv->flags);
                 if (iwcm_deref_id(cm_id_priv)) {
-                        if (test_bit(IWCM_F_CALLBACK_DESTROY,
-                                     &cm_id_priv->flags)) {
+                        if (destroy_id) {
                                 BUG_ON(!list_empty(&cm_id_priv->work_list));
                                 free_cm_id(cm_id_priv);
                         }