[SCSI] megaraid_sas: switch fw_outstanding to an atomic_t

This patch( originally submitted by Christoph Hellwig) removes
instance_lock and changes fw_outstanding variable data type to
atomic_t.
Signed-off-by: Sumant Patro <Sumant.Patro@lsil.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

Documentation/scsi/ChangeLog.megaraid_sas

+
+1 Release Date    : Wed Feb 03 14:31:44 PST 2006 - Sumant Patro <Sumant.Patro@lsil.com>
+2 Current Version : 00.00.02.04
+3 Older Version   : 00.00.02.04 
+
+i.	Remove superflous instance_lock
+
+	gets rid of the otherwise superflous instance_lock and avoids an unsave 
+	unsynchronized access in the error handler.
+
+		- Christoph Hellwig <hch@lst.de>
+
+
 1 Release Date    : Wed Feb 03 14:31:44 PST 2006 - Sumant Patro <Sumant.Patro@lsil.com>
 2 Current Version : 00.00.02.04
 3 Older Version   : 00.00.02.04 

drivers/scsi/megaraid/megaraid_sas.c

@@ -741,7 +741,6 @@ static int
 megasas_queue_command(struct scsi_cmnd *scmd, void (*done) (struct scsi_cmnd *))
 {
 	u32 frame_count;
-	unsigned long flags;
 	struct megasas_cmd *cmd;
 	struct megasas_instance *instance;
 
@@ -776,9 +775,7 @@ megasas_queue_command(struct scsi_cmnd *scmd, void (*done) (struct scsi_cmnd *))
 	/*
 	 * Issue the command to the FW
 	 */
-	spin_lock_irqsave(&instance->instance_lock, flags);
-	instance->fw_outstanding++;
-	spin_unlock_irqrestore(&instance->instance_lock, flags);
+	atomic_inc(&instance->fw_outstanding);
 
 	instance->instancet->fire_cmd(cmd->frame_phys_addr ,cmd->frame_count-1,instance->reg_set);
 
@@ -826,19 +823,20 @@ static int megasas_wait_for_outstanding(struct megasas_instance *instance)
 
 	for (i = 0; i < wait_time; i++) {
 
-		if (!instance->fw_outstanding)
+		int outstanding = atomic_read(&instance->fw_outstanding);
+
+		if (!outstanding)
 			break;
 
 		if (!(i % MEGASAS_RESET_NOTICE_INTERVAL)) {
 			printk(KERN_NOTICE "megasas: [%2d]waiting for %d "
-			       "commands to complete\n", i,
-			       instance->fw_outstanding);
+			       "commands to complete\n",i,outstanding);
 		}
 
 		msleep(1000);
 	}
 
-	if (instance->fw_outstanding) {
+	if (atomic_read(&instance->fw_outstanding)) {
 		instance->hw_crit_error = 1;
 		return FAILED;
 	}
@@ -1050,7 +1048,6 @@ megasas_complete_cmd(struct megasas_instance *instance, struct megasas_cmd *cmd,
 {
 	int exception = 0;
 	struct megasas_header *hdr = &cmd->frame->hdr;
-	unsigned long flags;
 
 	if (cmd->scmd) {
 		cmd->scmd->SCp.ptr = (char *)0;
@@ -1082,9 +1079,7 @@ megasas_complete_cmd(struct megasas_instance *instance, struct megasas_cmd *cmd,
 
 		if (exception) {
 
-			spin_lock_irqsave(&instance->instance_lock, flags);
-			instance->fw_outstanding--;
-			spin_unlock_irqrestore(&instance->instance_lock, flags);
+			atomic_dec(&instance->fw_outstanding);
 
 			megasas_unmap_sgbuf(instance, cmd);
 			cmd->scmd->scsi_done(cmd->scmd);
@@ -1132,9 +1127,7 @@ megasas_complete_cmd(struct megasas_instance *instance, struct megasas_cmd *cmd,
 			break;
 		}
 
-		spin_lock_irqsave(&instance->instance_lock, flags);
-		instance->fw_outstanding--;
-		spin_unlock_irqrestore(&instance->instance_lock, flags);
+		atomic_dec(&instance->fw_outstanding);
 
 		megasas_unmap_sgbuf(instance, cmd);
 		cmd->scmd->scsi_done(cmd->scmd);
@@ -2171,11 +2164,12 @@ megasas_probe_one(struct pci_dev *pdev, const struct pci_device_id *id)
 	 */
 	INIT_LIST_HEAD(&instance->cmd_pool);
 
+	atomic_set(&instance->fw_outstanding,0);
+
 	init_waitqueue_head(&instance->int_cmd_wait_q);
 	init_waitqueue_head(&instance->abort_cmd_wait_q);
 
 	spin_lock_init(&instance->cmd_pool_lock);
-	spin_lock_init(&instance->instance_lock);
 
 	sema_init(&instance->aen_mutex, 1);
 	sema_init(&instance->ioctl_sem, MEGASAS_INT_CMDS);

drivers/scsi/megaraid/megaraid_sas.h

@@ -1077,9 +1077,8 @@ struct megasas_instance {
 	struct pci_dev *pdev;
 	u32 unique_id;
 
-	u32 fw_outstanding;
+	atomic_t fw_outstanding;
 	u32 hw_crit_error;
-	spinlock_t instance_lock;
 
 	struct megasas_instance_template *instancet;
 };