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Subject[patch 22/86] RDMA/core: Fix kernel panic by always initializing qp->usecnt
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>

commit e47e321a35c741ee41b67976f8c6a3a7a42bc5c0 upstream.

We have just been investigating kernel panics related to
cq->ibcq.event_handler() completion calls. The problem is that
ib_destroy_qp() fails with -EBUSY.

Further investigation revealed qp->usecnt is not initialized. This
counter was introduced in linux-3.2 by commit 0e0ec7e0638e
("RDMA/core: Export ib_open_qp() to share XRC TGT QPs") but it only
gets initialized for IB_QPT_XRC_TGT, but it is checked in
ib_destroy_qp() for any QP type.

Fix this by initializing qp->usecnt for every QP we create.

Signed-off-by: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>
Signed-off-by: Sven Breuner <sven.breuner@itwm.fraunhofer.de>

[ Initialize qp->usecnt in uverbs too. - Sean ]

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/infiniband/core/uverbs_cmd.c | 1 +
drivers/infiniband/core/verbs.c | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -1485,6 +1485,7 @@ ssize_t ib_uverbs_create_qp(struct ib_uv
qp->event_handler = attr.event_handler;
qp->qp_context = attr.qp_context;
qp->qp_type = attr.qp_type;
+ atomic_set(&qp->usecnt, 0);
atomic_inc(&pd->usecnt);
atomic_inc(&attr.send_cq->usecnt);
if (attr.recv_cq)
--- a/drivers/infiniband/core/verbs.c
+++ b/drivers/infiniband/core/verbs.c
@@ -421,6 +421,7 @@ struct ib_qp *ib_create_qp(struct ib_pd
qp->uobject = NULL;
qp->qp_type = qp_init_attr->qp_type;

+ atomic_set(&qp->usecnt, 0);
if (qp_init_attr->qp_type == IB_QPT_XRC_TGT) {
qp->event_handler = __ib_shared_qp_event_handler;
qp->qp_context = qp;
@@ -430,7 +431,6 @@ struct ib_qp *ib_create_qp(struct ib_pd
qp->xrcd = qp_init_attr->xrcd;
atomic_inc(&qp_init_attr->xrcd->usecnt);
INIT_LIST_HEAD(&qp->open_list);
- atomic_set(&qp->usecnt, 0);

real_qp = qp;
qp = __ib_open_qp(real_qp, qp_init_attr->event_handler,



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