linux-kernel - [PATCH 3.13 125/163] IB/qib: Correct reference counting in debugfs qp

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Date:	Thu,  9 Oct 2014 14:02:30 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Mike Marciniszyn <mike.marciniszyn@...el.com>,
	Roland Dreier <roland@...estorage.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.13 125/163] IB/qib: Correct reference counting in debugfs qp_stats

3.13.11.9 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Marciniszyn <mike.marciniszyn@...el.com>

commit 85cbb7c728bf39c45a9789b88c9471c0d7a58b0e upstream.

This particular reference count is not needed with the rcu protection,
and the current code leaks a reference count, causing a hang in
qib_qp_destroy().

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@...el.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@...el.com>
Signed-off-by: Roland Dreier <roland@...estorage.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/infiniband/hw/qib/qib_debugfs.c | 3 ++-
 drivers/infiniband/hw/qib/qib_qp.c      | 8 --------
 2 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/drivers/infiniband/hw/qib/qib_debugfs.c b/drivers/infiniband/hw/qib/qib_debugfs.c
index 799a0c3..6abd3ed 100644
--- a/drivers/infiniband/hw/qib/qib_debugfs.c
+++ b/drivers/infiniband/hw/qib/qib_debugfs.c
@@ -193,6 +193,7 @@ static void *_qp_stats_seq_start(struct seq_file *s, loff_t *pos)
 	struct qib_qp_iter *iter;
 	loff_t n = *pos;
 
+	rcu_read_lock();
 	iter = qib_qp_iter_init(s->private);
 	if (!iter)
 		return NULL;
@@ -224,7 +225,7 @@ static void *_qp_stats_seq_next(struct seq_file *s, void *iter_ptr,
 
 static void _qp_stats_seq_stop(struct seq_file *s, void *iter_ptr)
 {
-	/* nothing for now */
+	rcu_read_unlock();
 }
 
 static int _qp_stats_seq_show(struct seq_file *s, void *iter_ptr)
diff --git a/drivers/infiniband/hw/qib/qib_qp.c b/drivers/infiniband/hw/qib/qib_qp.c
index 3cca55b..2c018ba 100644
--- a/drivers/infiniband/hw/qib/qib_qp.c
+++ b/drivers/infiniband/hw/qib/qib_qp.c
@@ -1324,7 +1324,6 @@ int qib_qp_iter_next(struct qib_qp_iter *iter)
 	struct qib_qp *pqp = iter->qp;
 	struct qib_qp *qp;
 
-	rcu_read_lock();
 	for (; n < dev->qp_table_size; n++) {
 		if (pqp)
 			qp = rcu_dereference(pqp->next);
@@ -1332,18 +1331,11 @@ int qib_qp_iter_next(struct qib_qp_iter *iter)
 			qp = rcu_dereference(dev->qp_table[n]);
 		pqp = qp;
 		if (qp) {
-			if (iter->qp)
-				atomic_dec(&iter->qp->refcount);
-			atomic_inc(&qp->refcount);
-			rcu_read_unlock();
 			iter->qp = qp;
 			iter->n = n;
 			return 0;
 		}
 	}
-	rcu_read_unlock();
-	if (iter->qp)
-		atomic_dec(&iter->qp->refcount);
 	return ret;
 }
 
-- 
1.9.1

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