scsi: convert host_busy to atomic_t

Avoid taking the host-wide host_lock to check the per-host queue limit. Instead we do an atomic_inc_return early on to grab our slot in the queue, and if necessary decrement it after finishing all checks. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Hannes Reinecke <hare@suse.de> Reviewed-by: Webb Scales <webbnh@hp.com> Acked-by: Jens Axboe <axboe@kernel.dk> Tested-by: Bart Van Assche <bvanassche@acm.org> Tested-by: Robert Elliott <elliott@hp.com>

scsi: convert host_busy to atomic_t
Avoid taking the host-wide host_lock to check the per-host queue limit. Instead we do an atomic_inc_return early on to grab our slot in the queue, and if necessary decrement it after finishing all checks. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Hannes Reinecke <hare@suse.de> Reviewed-by: Webb Scales <webbnh@hp.com> Acked-by: Jens Axboe <axboe@kernel.dk> Tested-by: Bart Van Assche <bvanassche@acm.org> Tested-by: Robert Elliott <elliott@hp.com>
Christoph Hellwig
1 parent 7ae65c0f96
Showing 9 changed files with 69 additions and 48 deletions Side-by-side Diff
drivers/scsi/advansys.c
drivers/scsi/libiscsi.c
drivers/scsi/libsas/sas_scsi_host.c
drivers/scsi/qlogicpti.c
drivers/scsi/scsi.c
drivers/scsi/scsi_error.c
drivers/scsi/scsi_lib.c
drivers/scsi/scsi_sysfs.c
include/scsi/scsi_host.h
@@ -2512,7 +2512,7 @@
  
 	printk("Scsi_Host at addr 0x%p, device %s\n", s, dev_name(boardp->dev));
 	printk(" host_busy %u, host_no %d,\n",
-	       s->host_busy, s->host_no);
+	       atomic_read(&s->host_busy), s->host_no);
  
 	printk(" base 0x%lx, io_port 0x%lx, irq %d,\n",
 	       (ulong)s->base, (ulong)s->io_port, boardp->irq);
@@ -3346,7 +3346,7 @@
  
 	seq_printf(m,
 		   " host_busy %u, max_id %u, max_lun %llu, max_channel %u\n",
-		   shost->host_busy, shost->max_id,
+		   atomic_read(&shost->host_busy), shost->max_id,
 		   shost->max_lun, shost->max_channel);
  
 	seq_printf(m,
@@ -2971,7 +2971,7 @@
 	 */
 	for (;;) {
 		spin_lock_irqsave(session->host->host_lock, flags);
-		if (!session->host->host_busy) { /* OK for ERL == 0 */
+		if (!atomic_read(&session->host->host_busy)) { /* OK for ERL == 0 */
 			spin_unlock_irqrestore(session->host->host_lock, flags);
 			break;
 		}
@@ -2979,7 +2979,7 @@
 		msleep_interruptible(500);
 		iscsi_conn_printk(KERN_INFO, conn, "iscsi conn_destroy(): "
 				  "host_busy %d host_failed %d\n",
-				  session->host->host_busy,
+				  atomic_read(&session->host->host_busy),
 				  session->host->host_failed);
 		/*
 		 * force eh_abort() to unblock
@@ -813,7 +813,7 @@
 	spin_unlock_irq(shost->host_lock);
  
 	SAS_DPRINTK("Enter %s busy: %d failed: %d\n",
-		    __func__, shost->host_busy, shost->host_failed);
+		    __func__, atomic_read(&shost->host_busy), shost->host_failed);
 	/*
 	 * Deal with commands that still have SAS tasks (i.e. they didn't
 	 * complete via the normal sas_task completion mechanism),
@@ -858,7 +858,8 @@
 		goto retry;
  
 	SAS_DPRINTK("--- Exit %s: busy: %d failed: %d tries: %d\n",
-		    __func__, shost->host_busy, shost->host_failed, tries);
+		    __func__, atomic_read(&shost->host_busy),
+		    shost->host_failed, tries);
 }
  
 enum blk_eh_timer_return sas_scsi_timed_out(struct scsi_cmnd *cmd)
@@ -959,7 +959,7 @@
 	/* Temporary workaround until bug is found and fixed (one bug has been found
 	   already, but fixing it makes things even worse) -jj */
 	int num_free = QLOGICPTI_REQ_QUEUE_LEN - REQ_QUEUE_DEPTH(in_ptr, out_ptr) - 64;
-	host->can_queue = host->host_busy + num_free;
+	host->can_queue = atomic_read(&host->host_busy) + num_free;
 	host->sg_tablesize = QLOGICPTI_MAX_SG(num_free);
 }
  
@@ -600,7 +600,7 @@
 			if (level > 3)
 				scmd_printk(KERN_INFO, cmd,
 					    "scsi host busy %d failed %d\n",
-					    cmd->device->host->host_busy,
+					    atomic_read(&cmd->device->host->host_busy),
 					    cmd->device->host->host_failed);
 		}
 	}
@@ -59,7 +59,7 @@
 /* called with shost->host_lock held */
 void scsi_eh_wakeup(struct Scsi_Host *shost)
 {
-	if (shost->host_busy == shost->host_failed) {
+	if (atomic_read(&shost->host_busy) == shost->host_failed) {
 		trace_scsi_eh_wakeup(shost);
 		wake_up_process(shost->ehandler);
 		SCSI_LOG_ERROR_RECOVERY(5, shost_printk(KERN_INFO, shost,
@@ -2164,7 +2164,7 @@
 	while (!kthread_should_stop()) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		if ((shost->host_failed == 0 && shost->host_eh_scheduled == 0) ||
-		    shost->host_failed != shost->host_busy) {
+		    shost->host_failed != atomic_read(&shost->host_busy)) {
 			SCSI_LOG_ERROR_RECOVERY(1,
 				shost_printk(KERN_INFO, shost,
 					     "scsi_eh_%d: sleeping\n",
@@ -2178,7 +2178,8 @@
 			shost_printk(KERN_INFO, shost,
 				     "scsi_eh_%d: waking up %d/%d/%d\n",
 				     shost->host_no, shost->host_eh_scheduled,
-				     shost->host_failed, shost->host_busy));
+				     shost->host_failed,
+				     atomic_read(&shost->host_busy)));
  
 		/*
 		 * We have a host that is failing for some reason.  Figure out
@@ -292,14 +292,17 @@
 	struct scsi_target *starget = scsi_target(sdev);
 	unsigned long flags;
  
-	spin_lock_irqsave(shost->host_lock, flags);
-	shost->host_busy--;
+	atomic_dec(&shost->host_busy);
 	atomic_dec(&starget->target_busy);
+
 	if (unlikely(scsi_host_in_recovery(shost) &&
-		     (shost->host_failed || shost->host_eh_scheduled)))
+		     (shost->host_failed || shost->host_eh_scheduled))) {
+		spin_lock_irqsave(shost->host_lock, flags);
 		scsi_eh_wakeup(shost);
-	spin_unlock(shost->host_lock);
-	spin_lock(sdev->request_queue->queue_lock);
+		spin_unlock_irqrestore(shost->host_lock, flags);
+	}
+
+	spin_lock_irqsave(sdev->request_queue->queue_lock, flags);
 	sdev->device_busy--;
 	spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
 }
@@ -367,7 +370,8 @@
  
 static inline int scsi_host_is_busy(struct Scsi_Host *shost)
 {
-	if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
+	if ((shost->can_queue > 0 &&
+	     atomic_read(&shost->host_busy) >= shost->can_queue) ||
 	    shost->host_blocked || shost->host_self_blocked)
 		return 1;
  
  
  
  
  
  
  
  
  
@@ -1334,38 +1338,54 @@
 				   struct Scsi_Host *shost,
 				   struct scsi_device *sdev)
 {
-	int ret = 0;
+	unsigned int busy;
  
-	spin_lock_irq(shost->host_lock);
-
 	if (scsi_host_in_recovery(shost))
-		goto out;
-	if (shost->host_busy == 0 && shost->host_blocked) {
+		return 0;
+
+	busy = atomic_inc_return(&shost->host_busy) - 1;
+	if (shost->host_blocked) {
+		if (busy)
+			goto starved;
+
 		/*
 		 * unblock after host_blocked iterates to zero
 		 */
-		if (--shost->host_blocked != 0)
-			goto out;
+		spin_lock_irq(shost->host_lock);
+		if (--shost->host_blocked != 0) {
+			spin_unlock_irq(shost->host_lock);
+			goto out_dec;
+		}
+		spin_unlock_irq(shost->host_lock);
  
 		SCSI_LOG_MLQUEUE(3,
 			shost_printk(KERN_INFO, shost,
 				     "unblocking host at zero depth\n"));
 	}
-	if (scsi_host_is_busy(shost)) {
-		if (list_empty(&sdev->starved_entry))
-			list_add_tail(&sdev->starved_entry, &shost->starved_list);
-		goto out;
-	}
  
+	if (shost->can_queue > 0 && busy >= shost->can_queue)
+		goto starved;
+	if (shost->host_self_blocked)
+		goto starved;
+
 	/* We're OK to process the command, so we can't be starved */
-	if (!list_empty(&sdev->starved_entry))
-		list_del_init(&sdev->starved_entry);
+	if (!list_empty(&sdev->starved_entry)) {
+		spin_lock_irq(shost->host_lock);
+		if (!list_empty(&sdev->starved_entry))
+			list_del_init(&sdev->starved_entry);
+		spin_unlock_irq(shost->host_lock);
+	}
  
-	shost->host_busy++;
-	ret = 1;
-out:
+	return 1;
+
+starved:
+	spin_lock_irq(shost->host_lock);
+	if (list_empty(&sdev->starved_entry))
+		list_add_tail(&sdev->starved_entry, &shost->starved_list);
 	spin_unlock_irq(shost->host_lock);
-	return ret;
+out_dec:
+	atomic_dec(&shost->host_busy);
+	return 0;
 }
  
 /*
  
@@ -1429,12 +1449,8 @@
 	 * with the locks as normal issue path does.
 	 */
 	sdev->device_busy++;
-	spin_unlock(sdev->request_queue->queue_lock);
-	spin_lock(shost->host_lock);
-	shost->host_busy++;
+	atomic_inc(&shost->host_busy);
 	atomic_inc(&starget->target_busy);
-	spin_unlock(shost->host_lock);
-	spin_lock(sdev->request_queue->queue_lock);
  
 	blk_complete_request(req);
 }
@@ -334,7 +334,6 @@
 static DEVICE_ATTR(eh_deadline, S_IRUGO | S_IWUSR, show_shost_eh_deadline, store_shost_eh_deadline);
  
 shost_rd_attr(unique_id, "%u\n");
-shost_rd_attr(host_busy, "%hu\n");
 shost_rd_attr(cmd_per_lun, "%hd\n");
 shost_rd_attr(can_queue, "%hd\n");
 shost_rd_attr(sg_tablesize, "%hu\n");
@@ -343,6 +342,14 @@
 shost_rd_attr(prot_capabilities, "%u\n");
 shost_rd_attr(prot_guard_type, "%hd\n");
 shost_rd_attr2(proc_name, hostt->proc_name, "%s\n");
+
+static ssize_t
+show_host_busy(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct Scsi_Host *shost = class_to_shost(dev);
+	return snprintf(buf, 20, "%d\n", atomic_read(&shost->host_busy));
+}
+static DEVICE_ATTR(host_busy, S_IRUGO, show_host_busy, NULL);
  
 static struct attribute *scsi_sysfs_shost_attrs[] = {
 	&dev_attr_unique_id.attr,
@@ -582,13 +582,9 @@
 	 */
 	struct blk_queue_tag	*bqt;
  
-	/*
-	 * The following two fields are protected with host_lock;
-	 * however, eh routines can safely access during eh processing
-	 * without acquiring the lock.
-	 */
-	unsigned int host_busy;		   /* commands actually active on low-level */
-	unsigned int host_failed;	   /* commands that failed. */
+	atomic_t host_busy;		   /* commands actually active on low-level */
+	unsigned int host_failed;	   /* commands that failed.
+					      protected by host_lock */
 	unsigned int host_eh_scheduled;    /* EH scheduled without command */
  
 	unsigned int host_no;  /* Used for IOCTL_GET_IDLUN, /proc/scsi et al. */
...	...	@@ -2512,7 +2512,7 @@
2512	2512
2513	2513	printk("Scsi_Host at addr 0x%p, device %s\n", s, dev_name(boardp->dev));
2514	2514	printk(" host_busy %u, host_no %d,\n",
2515		- s->host_busy, s->host_no);
	2515	+ atomic_read(&s->host_busy), s->host_no);
2516	2516
2517	2517	printk(" base 0x%lx, io_port 0x%lx, irq %d,\n",
2518	2518	(ulong)s->base, (ulong)s->io_port, boardp->irq);
...	...	@@ -3346,7 +3346,7 @@
3346	3346
3347	3347	seq_printf(m,
3348	3348	" host_busy %u, max_id %u, max_lun %llu, max_channel %u\n",
3349		- shost->host_busy, shost->max_id,
	3349	+ atomic_read(&shost->host_busy), shost->max_id,
3350	3350	shost->max_lun, shost->max_channel);
3351	3351
3352	3352	seq_printf(m,
...	...	@@ -2971,7 +2971,7 @@
2971	2971	*/
2972	2972	for (;;) {
2973	2973	spin_lock_irqsave(session->host->host_lock, flags);
2974		- if (!session->host->host_busy) { /* OK for ERL == 0 */
	2974	+ if (!atomic_read(&session->host->host_busy)) { /* OK for ERL == 0 */
2975	2975	spin_unlock_irqrestore(session->host->host_lock, flags);
2976	2976	break;
2977	2977	}
...	...	@@ -2979,7 +2979,7 @@
2979	2979	msleep_interruptible(500);
2980	2980	iscsi_conn_printk(KERN_INFO, conn, "iscsi conn_destroy(): "
2981	2981	"host_busy %d host_failed %d\n",
2982		- session->host->host_busy,
	2982	+ atomic_read(&session->host->host_busy),
2983	2983	session->host->host_failed);
2984	2984	/*
2985	2985	* force eh_abort() to unblock
...	...	@@ -813,7 +813,7 @@
813	813	spin_unlock_irq(shost->host_lock);
814	814
815	815	SAS_DPRINTK("Enter %s busy: %d failed: %d\n",
816		- __func__, shost->host_busy, shost->host_failed);
	816	+ __func__, atomic_read(&shost->host_busy), shost->host_failed);
817	817	/*
818	818	* Deal with commands that still have SAS tasks (i.e. they didn't
819	819	* complete via the normal sas_task completion mechanism),
...	...	@@ -858,7 +858,8 @@
858	858	goto retry;
859	859
860	860	SAS_DPRINTK("--- Exit %s: busy: %d failed: %d tries: %d\n",
861		- __func__, shost->host_busy, shost->host_failed, tries);
	861	+ __func__, atomic_read(&shost->host_busy),
	862	+ shost->host_failed, tries);
862	863	}
863	864
864	865	enum blk_eh_timer_return sas_scsi_timed_out(struct scsi_cmnd *cmd)
...	...	@@ -959,7 +959,7 @@
959	959	/* Temporary workaround until bug is found and fixed (one bug has been found
960	960	already, but fixing it makes things even worse) -jj */
961	961	int num_free = QLOGICPTI_REQ_QUEUE_LEN - REQ_QUEUE_DEPTH(in_ptr, out_ptr) - 64;
962		- host->can_queue = host->host_busy + num_free;
	962	+ host->can_queue = atomic_read(&host->host_busy) + num_free;
963	963	host->sg_tablesize = QLOGICPTI_MAX_SG(num_free);
964	964	}
965	965
...	...	@@ -600,7 +600,7 @@
600	600	if (level > 3)
601	601	scmd_printk(KERN_INFO, cmd,
602	602	"scsi host busy %d failed %d\n",
603		- cmd->device->host->host_busy,
	603	+ atomic_read(&cmd->device->host->host_busy),
604	604	cmd->device->host->host_failed);
605	605	}
606	606	}
...	...	@@ -59,7 +59,7 @@
59	59	/* called with shost->host_lock held */
60	60	void scsi_eh_wakeup(struct Scsi_Host *shost)
61	61	{
62		- if (shost->host_busy == shost->host_failed) {
	62	+ if (atomic_read(&shost->host_busy) == shost->host_failed) {
63	63	trace_scsi_eh_wakeup(shost);
64	64	wake_up_process(shost->ehandler);
65	65	SCSI_LOG_ERROR_RECOVERY(5, shost_printk(KERN_INFO, shost,
...	...	@@ -2164,7 +2164,7 @@
2164	2164	while (!kthread_should_stop()) {
2165	2165	set_current_state(TASK_INTERRUPTIBLE);
2166	2166	if ((shost->host_failed == 0 && shost->host_eh_scheduled == 0) \|\|
2167		- shost->host_failed != shost->host_busy) {
	2167	+ shost->host_failed != atomic_read(&shost->host_busy)) {
2168	2168	SCSI_LOG_ERROR_RECOVERY(1,
2169	2169	shost_printk(KERN_INFO, shost,
2170	2170	"scsi_eh_%d: sleeping\n",
...	...	@@ -2178,7 +2178,8 @@
2178	2178	shost_printk(KERN_INFO, shost,
2179	2179	"scsi_eh_%d: waking up %d/%d/%d\n",
2180	2180	shost->host_no, shost->host_eh_scheduled,
2181		- shost->host_failed, shost->host_busy));
	2181	+ shost->host_failed,
	2182	+ atomic_read(&shost->host_busy)));
2182	2183
2183	2184	/*
2184	2185	* We have a host that is failing for some reason. Figure out
...	...	@@ -292,14 +292,17 @@
292	292	struct scsi_target *starget = scsi_target(sdev);
293	293	unsigned long flags;
294	294
295		- spin_lock_irqsave(shost->host_lock, flags);
296		- shost->host_busy--;
	295	+ atomic_dec(&shost->host_busy);
297	296	atomic_dec(&starget->target_busy);
	297	+
298	298	if (unlikely(scsi_host_in_recovery(shost) &&
299		- (shost->host_failed \|\| shost->host_eh_scheduled)))
	299	+ (shost->host_failed \|\| shost->host_eh_scheduled))) {
	300	+ spin_lock_irqsave(shost->host_lock, flags);
300	301	scsi_eh_wakeup(shost);
301		- spin_unlock(shost->host_lock);
302		- spin_lock(sdev->request_queue->queue_lock);
	302	+ spin_unlock_irqrestore(shost->host_lock, flags);
	303	+ }
	304	+
	305	+ spin_lock_irqsave(sdev->request_queue->queue_lock, flags);
303	306	sdev->device_busy--;
304	307	spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
305	308	}
...	...	@@ -367,7 +370,8 @@
367	370
368	371	static inline int scsi_host_is_busy(struct Scsi_Host *shost)
369	372	{
370		- if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) \|\|
	373	+ if ((shost->can_queue > 0 &&
	374	+ atomic_read(&shost->host_busy) >= shost->can_queue) \|\|
371	375	shost->host_blocked \|\| shost->host_self_blocked)
372	376	return 1;
373	377
374	378
375	379
376	380
377	381
378	382
379	383
380	384
381	385
...	...	@@ -1334,38 +1338,54 @@
1334	1338	struct Scsi_Host *shost,
1335	1339	struct scsi_device *sdev)
1336	1340	{
1337		- int ret = 0;
	1341	+ unsigned int busy;
1338	1342
1339		- spin_lock_irq(shost->host_lock);
1340		-
1341	1343	if (scsi_host_in_recovery(shost))
1342		- goto out;
1343		- if (shost->host_busy == 0 && shost->host_blocked) {
	1344	+ return 0;
	1345	+
	1346	+ busy = atomic_inc_return(&shost->host_busy) - 1;
	1347	+ if (shost->host_blocked) {
	1348	+ if (busy)
	1349	+ goto starved;
	1350	+
1344	1351	/*
1345	1352	* unblock after host_blocked iterates to zero
1346	1353	*/
1347		- if (--shost->host_blocked != 0)
1348		- goto out;
	1354	+ spin_lock_irq(shost->host_lock);
	1355	+ if (--shost->host_blocked != 0) {
	1356	+ spin_unlock_irq(shost->host_lock);
	1357	+ goto out_dec;
	1358	+ }
	1359	+ spin_unlock_irq(shost->host_lock);
1349	1360
1350	1361	SCSI_LOG_MLQUEUE(3,
1351	1362	shost_printk(KERN_INFO, shost,
1352	1363	"unblocking host at zero depth\n"));
1353	1364	}
1354		- if (scsi_host_is_busy(shost)) {
1355		- if (list_empty(&sdev->starved_entry))
1356		- list_add_tail(&sdev->starved_entry, &shost->starved_list);
1357		- goto out;
1358		- }
1359	1365
	1366	+ if (shost->can_queue > 0 && busy >= shost->can_queue)
	1367	+ goto starved;
	1368	+ if (shost->host_self_blocked)
	1369	+ goto starved;
	1370	+
1360	1371	/* We're OK to process the command, so we can't be starved */
1361		- if (!list_empty(&sdev->starved_entry))
1362		- list_del_init(&sdev->starved_entry);
	1372	+ if (!list_empty(&sdev->starved_entry)) {
	1373	+ spin_lock_irq(shost->host_lock);
	1374	+ if (!list_empty(&sdev->starved_entry))
	1375	+ list_del_init(&sdev->starved_entry);
	1376	+ spin_unlock_irq(shost->host_lock);
	1377	+ }
1363	1378
1364		- shost->host_busy++;
1365		- ret = 1;
1366		-out:
	1379	+ return 1;
	1380	+
	1381	+starved:
	1382	+ spin_lock_irq(shost->host_lock);
	1383	+ if (list_empty(&sdev->starved_entry))
	1384	+ list_add_tail(&sdev->starved_entry, &shost->starved_list);
1367	1385	spin_unlock_irq(shost->host_lock);
1368		- return ret;
	1386	+out_dec:
	1387	+ atomic_dec(&shost->host_busy);
	1388	+ return 0;
1369	1389	}
1370	1390
1371	1391	/*
1372	1392
...	...	@@ -1429,12 +1449,8 @@
1429	1449	* with the locks as normal issue path does.
1430	1450	*/
1431	1451	sdev->device_busy++;
1432		- spin_unlock(sdev->request_queue->queue_lock);
1433		- spin_lock(shost->host_lock);
1434		- shost->host_busy++;
	1452	+ atomic_inc(&shost->host_busy);
1435	1453	atomic_inc(&starget->target_busy);
1436		- spin_unlock(shost->host_lock);
1437		- spin_lock(sdev->request_queue->queue_lock);
1438	1454
1439	1455	blk_complete_request(req);
1440	1456	}
...	...	@@ -334,7 +334,6 @@
334	334	static DEVICE_ATTR(eh_deadline, S_IRUGO \| S_IWUSR, show_shost_eh_deadline, store_shost_eh_deadline);
335	335
336	336	shost_rd_attr(unique_id, "%u\n");
337		-shost_rd_attr(host_busy, "%hu\n");
338	337	shost_rd_attr(cmd_per_lun, "%hd\n");
339	338	shost_rd_attr(can_queue, "%hd\n");
340	339	shost_rd_attr(sg_tablesize, "%hu\n");
...	...	@@ -343,6 +342,14 @@
343	342	shost_rd_attr(prot_capabilities, "%u\n");
344	343	shost_rd_attr(prot_guard_type, "%hd\n");
345	344	shost_rd_attr2(proc_name, hostt->proc_name, "%s\n");
	345	+
	346	+static ssize_t
	347	+show_host_busy(struct device dev, struct device_attribute attr, char *buf)
	348	+{
	349	+ struct Scsi_Host *shost = class_to_shost(dev);
	350	+ return snprintf(buf, 20, "%d\n", atomic_read(&shost->host_busy));
	351	+}
	352	+static DEVICE_ATTR(host_busy, S_IRUGO, show_host_busy, NULL);
346	353
347	354	static struct attribute *scsi_sysfs_shost_attrs[] = {
348	355	&dev_attr_unique_id.attr,
...	...	@@ -582,13 +582,9 @@
582	582	*/
583	583	struct blk_queue_tag *bqt;
584	584
585		- /*
586		- * The following two fields are protected with host_lock;
587		- * however, eh routines can safely access during eh processing
588		- * without acquiring the lock.
589		- */
590		- unsigned int host_busy; /* commands actually active on low-level */
591		- unsigned int host_failed; /* commands that failed. */
	585	+ atomic_t host_busy; /* commands actually active on low-level */
	586	+ unsigned int host_failed; /* commands that failed.
	587	+ protected by host_lock */
592	588	unsigned int host_eh_scheduled; /* EH scheduled without command */
593	589
594	590	unsigned int host_no; /* Used for IOCTL_GET_IDLUN, /proc/scsi et al. */