linux-kernel - [PATCH] [196/275] IB/cm: Bump reference count on cm

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Date:	Wed, 30 Mar 2011 14:07:20 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	sean.hefty@...el.com, dledford@...hat.com, roland@...estorage.com,
	gregkh@...e.de, ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	stable@...nel.org, tim.bird@...sony.com
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 <sean.hefty@...el.com>

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@...el.com>
Acked-by: Doug Ledford <dledford@...hat.com>
Signed-off-by: Roland Dreier <roland@...estorage.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 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(&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;
--
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