Patch "IB/hfi1,IB/qib: Fix qp_stats sleep with rcu read lock held" has been added to the 4.7-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    IB/hfi1,IB/qib: Fix qp_stats sleep with rcu read lock held

to the 4.7-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ib-hfi1-ib-qib-fix-qp_stats-sleep-with-rcu-read-lock-held.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From c62fb260a86dde3df5b2905432caa0e9f6898434 Mon Sep 17 00:00:00 2001
From: Mike Marciniszyn <mike.marciniszyn@intel.com>
Date: Fri, 12 Aug 2016 11:17:37 -0400
Subject: IB/hfi1,IB/qib: Fix qp_stats sleep with rcu read lock held

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

commit c62fb260a86dde3df5b2905432caa0e9f6898434 upstream.

The qp init function does a kzalloc() while holding the RCU
lock that encounters the following warning with a debug kernel
when a cat of the qp_stats is done:

[  231.723948] rcu_scheduler_active = 1, debug_locks = 0
[  231.731939] 3 locks held by cat/11355:
[  231.736492]  #0:  (debugfs_srcu){......}, at: [<ffffffff813001a5>] debugfs_use_file_start+0x5/0x90
[  231.746955]  #1:  (&p->lock){+.+.+.}, at: [<ffffffff81289a6c>] seq_read+0x4c/0x3c0
[  231.755873]  #2:  (rcu_read_lock){......}, at: [<ffffffffa0a0c535>] _qp_stats_seq_start+0x5/0xd0 [hfi1]
[  231.766862]

The init functions do an implicit next which requires the rcu read lock
before the kzalloc().

Fix for both drivers is to change the scope of the init function to only
do the allocation and the initialization of the just allocated iter.

The implict next is moved back into the respective start functions to fix
the issue.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/infiniband/hw/hfi1/debugfs.c    |   14 +++++++++-----
 drivers/infiniband/hw/hfi1/qp.c         |    4 ----
 drivers/infiniband/hw/qib/qib_debugfs.c |   12 +++++++++---
 drivers/infiniband/hw/qib/qib_qp.c      |    4 ----
 4 files changed, 18 insertions(+), 16 deletions(-)

--- a/drivers/infiniband/hw/hfi1/debugfs.c
+++ b/drivers/infiniband/hw/hfi1/debugfs.c
@@ -223,28 +223,32 @@ DEBUGFS_SEQ_FILE_OPEN(ctx_stats)
 DEBUGFS_FILE_OPS(ctx_stats);
 
 static void *_qp_stats_seq_start(struct seq_file *s, loff_t *pos)
-__acquires(RCU)
+	__acquires(RCU)
 {
 	struct qp_iter *iter;
 	loff_t n = *pos;
 
-	rcu_read_lock();
 	iter = qp_iter_init(s->private);
+
+	/* stop calls rcu_read_unlock */
+	rcu_read_lock();
+
 	if (!iter)
 		return NULL;
 
-	while (n--) {
+	do {
 		if (qp_iter_next(iter)) {
 			kfree(iter);
 			return NULL;
 		}
-	}
+	} while (n--);
 
 	return iter;
 }
 
 static void *_qp_stats_seq_next(struct seq_file *s, void *iter_ptr,
 				loff_t *pos)
+	__must_hold(RCU)
 {
 	struct qp_iter *iter = iter_ptr;
 
@@ -259,7 +263,7 @@ static void *_qp_stats_seq_next(struct s
 }
 
 static void _qp_stats_seq_stop(struct seq_file *s, void *iter_ptr)
-__releases(RCU)
+	__releases(RCU)
 {
 	rcu_read_unlock();
 }
--- a/drivers/infiniband/hw/hfi1/qp.c
+++ b/drivers/infiniband/hw/hfi1/qp.c
@@ -595,10 +595,6 @@ struct qp_iter *qp_iter_init(struct hfi1
 
 	iter->dev = dev;
 	iter->specials = dev->rdi.ibdev.phys_port_cnt * 2;
-	if (qp_iter_next(iter)) {
-		kfree(iter);
-		return NULL;
-	}
 
 	return iter;
 }
--- a/drivers/infiniband/hw/qib/qib_debugfs.c
+++ b/drivers/infiniband/hw/qib/qib_debugfs.c
@@ -189,27 +189,32 @@ static int _ctx_stats_seq_show(struct se
 DEBUGFS_FILE(ctx_stats)
 
 static void *_qp_stats_seq_start(struct seq_file *s, loff_t *pos)
+	__acquires(RCU)
 {
 	struct qib_qp_iter *iter;
 	loff_t n = *pos;
 
-	rcu_read_lock();
 	iter = qib_qp_iter_init(s->private);
+
+	/* stop calls rcu_read_unlock */
+	rcu_read_lock();
+
 	if (!iter)
 		return NULL;
 
-	while (n--) {
+	do {
 		if (qib_qp_iter_next(iter)) {
 			kfree(iter);
 			return NULL;
 		}
-	}
+	} while (n--);
 
 	return iter;
 }
 
 static void *_qp_stats_seq_next(struct seq_file *s, void *iter_ptr,
 				   loff_t *pos)
+	__must_hold(RCU)
 {
 	struct qib_qp_iter *iter = iter_ptr;
 
@@ -224,6 +229,7 @@ static void *_qp_stats_seq_next(struct s
 }
 
 static void _qp_stats_seq_stop(struct seq_file *s, void *iter_ptr)
+	__releases(RCU)
 {
 	rcu_read_unlock();
 }
--- a/drivers/infiniband/hw/qib/qib_qp.c
+++ b/drivers/infiniband/hw/qib/qib_qp.c
@@ -530,10 +530,6 @@ struct qib_qp_iter *qib_qp_iter_init(str
 		return NULL;
 
 	iter->dev = dev;
-	if (qib_qp_iter_next(iter)) {
-		kfree(iter);
-		return NULL;
-	}
 
 	return iter;
 }


Patches currently in stable-queue which might be from mike.marciniszyn@intel.com are

queue-4.7/ib-hfi1-ib-qib-fix-qp_stats-sleep-with-rcu-read-lock-held.patch