IB/cm: Bump reference count on cm_id before invoking callback

When processing a SIDR REQ, the ib_cm allocates a new cm_id.  The
refcount of the cm_id is initialized to 1.  However, cm_process_work
will decrement the refcount after invoking all callbacks.  The result
is that the cm_id will end up with refcount set to 0 by the end of the
sidr req handler.

If a user tries to destroy the cm_id, the destruction will proceed,
under the incorrect assumption that no other threads are referencing
the cm_id.  This can lead to a crash when the cm callback thread tries
to access the cm_id.

This problem was noticed as part of a larger investigation with kernel
crashes in the rdma_cm when running on a real time OS.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Acked-by: Doug Ledford <dledford@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index 64e0903091a8679f9f14490873f68c03baef8cca..1d9616be419222d16a03a02943ba3f49d6f5c398 100644 (file)
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -2989,6 +2989,7 @@ static int cm_sidr_req_handler(struct cm_work *work)
                goto out; /* No match. */
        }
        atomic_inc(&cur_cm_id_priv->refcount);
+       atomic_inc(&cm_id_priv->refcount);
        spin_unlock_irq(&cm.lock);
 
        cm_id_priv->id.cm_handler = cur_cm_id_priv->id.cm_handler;