[3.13.y.z extended stable] Patch "IB/qib: Correct reference counting in debugfs qp_stats" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    IB/qib: Correct reference counting in debugfs qp_stats

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 609adca94f18d2197b980f77e6709bd231adceda Mon Sep 17 00:00:00 2001
From: Mike Marciniszyn <mike.marciniszyn at intel.com>
Date: Fri, 19 Sep 2014 08:32:19 -0400
Subject: IB/qib: Correct reference counting in debugfs qp_stats

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 at intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn at intel.com>
Signed-off-by: Roland Dreier <roland at purestorage.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.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