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Subject[PATCH] [196/275] IB/cm: Bump reference count on cm_id before invoking callback
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

From: Sean Hefty <>

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 <>
Acked-by: Doug Ledford <>
Signed-off-by: Roland Dreier <>
Signed-off-by: Greg Kroah-Hartman <>
Signed-off-by: Andi Kleen <>

drivers/infiniband/core/cm.c | 1 +
1 file changed, 1 insertion(+)

Index: linux-2.6.35.y/drivers/infiniband/core/cm.c
--- linux-2.6.35.y.orig/drivers/infiniband/core/cm.c 2011-03-29 22:50:42.296176166 -0700
+++ linux-2.6.35.y/drivers/infiniband/core/cm.c 2011-03-29 23:03:02.367239599 -0700
@@ -2987,6 +2987,7 @@
goto out; /* No match. */
+ atomic_inc(&cm_id_priv->refcount);

cm_id_priv->id.cm_handler = cur_cm_id_priv->id.cm_handler;

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