[34-longterm 178/247] IB/cm: Bump reference count on cm_id before invoking callback

[Paul Gortmaker]

From: Sean Hefty <sean.hefty@xxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 29963437a48475036353b95ab142bf199adb909e upstream.

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@xxxxxxxxx>
Acked-by: Doug Ledford <dledford@xxxxxxxxxx>
Signed-off-by: Roland Dreier <roland@xxxxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 drivers/infiniband/core/cm.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index ad63b79..2422945 100644
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -2987,6 +2987,7 @@ 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;
-- 
1.7.4.4

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