From 00b2d9d6d05b56fc1d77071ff8ccbd2c65b48dec Mon Sep 17 00:00:00 2001
From: Vaughan Cao <vaughan.cao@oracle.com>
Date: Thu, 29 Aug 2013 10:00:37 +0800
Subject: [SCSI] sg: no need sg_open_exclusive_lock

Open exclusive check is protected by o_sem, no need sg_open_exclusive_lock.
@exclude is used to record which type of rwsem we are holding.

Signed-off-by: Vaughan Cao <vaughan.cao@oracle.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 4efa9b5..d4af132 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -105,8 +105,6 @@ static int scatter_elem_sz_prev = SG_SCATTER_SZ;
 static int sg_add(struct device *, struct class_interface *);
 static void sg_remove(struct device *, struct class_interface *);
 
-static DEFINE_SPINLOCK(sg_open_exclusive_lock);
-
 static DEFINE_IDR(sg_index_idr);
 static DEFINE_RWLOCK(sg_index_lock);	/* Also used to lock
 							   file descriptor list for device */
@@ -176,7 +174,6 @@ typedef struct sg_device { /* holds the state of each scsi generic device */
 	struct list_head sfds;
 	struct rw_semaphore o_sem;	/* exclude open should hold this rwsem */
 	volatile char detached;	/* 0->attached, 1->detached pending removal */
-	/* exclude protected by sg_open_exclusive_lock */
 	char exclude;		/* opened for exclusive access */
 	char sgdebug;		/* 0->off, 1->sense, 9->dump dev, 10-> all devs */
 	struct gendisk *disk;
@@ -225,27 +222,6 @@ static int sg_allow_access(struct file *filp, unsigned char *cmd)
 	return blk_verify_command(cmd, filp->f_mode & FMODE_WRITE);
 }
 
-static int get_exclude(Sg_device *sdp)
-{
-	unsigned long flags;
-	int ret;
-
-	spin_lock_irqsave(&sg_open_exclusive_lock, flags);
-	ret = sdp->exclude;
-	spin_unlock_irqrestore(&sg_open_exclusive_lock, flags);
-	return ret;
-}
-
-static int set_exclude(Sg_device *sdp, char val)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&sg_open_exclusive_lock, flags);
-	sdp->exclude = val;
-	spin_unlock_irqrestore(&sg_open_exclusive_lock, flags);
-	return val;
-}
-
 static int sfds_list_empty(Sg_device *sdp)
 {
 	unsigned long flags;
@@ -317,7 +293,7 @@ sg_open(struct inode *inode, struct file *filp)
 	}
 	/* Since write lock is held, no need to check sfd_list */
 	if (flags & O_EXCL)
-		set_exclude(sdp, 1);
+		sdp->exclude = 1;	/* used by release lock */
 
 	if (sdp->detached) {
 		retval = -ENODEV;
@@ -337,7 +313,7 @@ sg_open(struct inode *inode, struct file *filp)
 		retval = -ENOMEM;
 sem_out:
 		if (flags & O_EXCL) {
-			set_exclude(sdp, 0);	/* undo if error */
+			sdp->exclude = 0;	/* undo if error */
 			up_write(&sdp->o_sem);
 		} else
 			up_read(&sdp->o_sem);
@@ -364,8 +340,8 @@ sg_release(struct inode *inode, struct file *filp)
 		return -ENXIO;
 	SCSI_LOG_TIMEOUT(3, printk("sg_release: %s\n", sdp->disk->disk_name));
 
-	excl = get_exclude(sdp);
-	set_exclude(sdp, 0);
+	excl = sdp->exclude;
+	sdp->exclude = 0;
 	if (excl)
 		up_write(&sdp->o_sem);
 	else
@@ -2622,7 +2598,7 @@ static int sg_proc_seq_show_debug(struct seq_file *s, void *v)
 			     scsidp->lun,
 			     scsidp->host->hostt->emulated);
 		seq_printf(s, " sg_tablesize=%d excl=%d\n",
-			   sdp->sg_tablesize, get_exclude(sdp));
+			   sdp->sg_tablesize, sdp->exclude);
 		sg_proc_debug_helper(s, sdp);
 	}
 	read_unlock_irqrestore(&sg_index_lock, iflags);
-- 
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