linux-kernel - [PATCH 1/2] loop : change lo_refcnt from int to atomic

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Date:	Mon, 28 Apr 2008 10:08:18 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	jens.axboe@...cle.com
Subject: [PATCH 1/2] loop : change lo_refcnt from int to atomic_t

It's not necessary to use lo_ctl_mutex to lock lo_refcnt. 

So here use atomic_t instead of int for lo_refcnt and leave lo_ctl_mutex just
for ioctl use.

Signed-off-by: Dave Young <hidave.darkstar@...il.com>

---
drivers/block/loop.c |   12 +++++-------
include/linux/loop.h |    2 +-
2 files changed, 6 insertions(+), 8 deletions(-)

diff -upr linux/drivers/block/loop.c linux.new/drivers/block/loop.c
--- linux/drivers/block/loop.c	2008-04-25 10:10:25.000000000 +0800
+++ linux.new/drivers/block/loop.c	2008-04-25 10:30:54.000000000 +0800
@@ -891,7 +891,7 @@ static int loop_clr_fd(struct loop_devic
 	if (lo->lo_state != Lo_bound)
 		return -ENXIO;
 
-	if (lo->lo_refcnt > 1)	/* we needed one fd for the ioctl */
+	if (atomic_read(&lo->lo_refcnt) > 1)/* we needed one fd for the ioctl */
 		return -EBUSY;
 
 	if (filp == NULL)
@@ -1331,9 +1331,7 @@ static int lo_open(struct inode *inode, 
 {
 	struct loop_device *lo = inode->i_bdev->bd_disk->private_data;
 
-	mutex_lock(&lo->lo_ctl_mutex);
-	lo->lo_refcnt++;
-	mutex_unlock(&lo->lo_ctl_mutex);
+	atomic_inc(&lo->lo_refcnt);
 
 	return 0;
 }
@@ -1342,10 +1340,10 @@ static int lo_release(struct inode *inod
 {
 	struct loop_device *lo = inode->i_bdev->bd_disk->private_data;
 
-	mutex_lock(&lo->lo_ctl_mutex);
-	--lo->lo_refcnt;
+	atomic_dec(&lo->lo_refcnt);
 
-	if ((lo->lo_flags & LO_FLAGS_AUTOCLEAR) && !lo->lo_refcnt)
+	mutex_lock(&lo->lo_ctl_mutex);
+	if ((lo->lo_flags & LO_FLAGS_AUTOCLEAR) && !atomic_read(&lo->lo_refcnt))
 		loop_clr_fd(lo, inode->i_bdev);
 
 	mutex_unlock(&lo->lo_ctl_mutex);
diff -upr linux/include/linux/loop.h linux.new/include/linux/loop.h
--- linux/include/linux/loop.h	2008-04-25 10:31:23.000000000 +0800
+++ linux.new/include/linux/loop.h	2008-04-25 10:31:34.000000000 +0800
@@ -30,7 +30,7 @@ struct loop_func_table;
 
 struct loop_device {
 	int		lo_number;
-	int		lo_refcnt;
+	atomic_t	lo_refcnt;
 	loff_t		lo_offset;
 	loff_t		lo_sizelimit;
 	int		lo_flags;
--
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