linux-kernel - [PATCH 2/4] chardev: Increment cdev reference count when i

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Date:	Tue,  4 Nov 2014 11:27:29 +0100
From:	Jan Kara <jack@...e.cz>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: [PATCH 2/4] chardev: Increment cdev reference count when i_cdev references it

Currently i_cdev reference to a character device isn't accounted in the
reference count of the character device. This then requires us to track
all references through a list of all inodes referencing a character
device which is somewhat clumsy and requires list_head in each inode in
the system.

So make i_cdev a reference like any other.

Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/char_dev.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index f77f7702fabe..518b3016ab92 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -388,12 +388,13 @@ static int chrdev_open(struct inode *inode, struct file *filp)
 		   we dropped the lock. */
 		p = inode->i_cdev;
 		if (!p) {
+			/* Use reference from kobj_lookup for i_cdev ref */
 			inode->i_cdev = p = new;
 			list_add(&inode->i_devices, &p->list);
 			new = NULL;
-		} else if (!cdev_get(p))
-			ret = -ENXIO;
-	} else if (!cdev_get(p))
+		}
+	}
+	if (!cdev_get(p))
 		ret = -ENXIO;
 	spin_unlock(&cdev_lock);
 	cdev_put(new);
@@ -421,10 +422,15 @@ static int chrdev_open(struct inode *inode, struct file *filp)
 
 void cd_forget(struct inode *inode)
 {
+	struct cdev *to_put;
+
 	spin_lock(&cdev_lock);
 	list_del_init(&inode->i_devices);
+	to_put = inode->i_cdev;
 	inode->i_cdev = NULL;
 	spin_unlock(&cdev_lock);
+	if (to_put)
+		cdev_put(to_put);
 }
 
 static void cdev_purge(struct cdev *cdev)
-- 
1.8.1.4

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