Commit cd9070c9 authored by Christoph Hellwig's avatar Christoph Hellwig
Browse files

scsi: fix the {host,target,device}_blocked counter mess 



Seems like these counters are missing any sort of synchronization for
updates, as a over 10 year old comment from me noted.  Fix this by
using atomic counters, and while we're at it also make sure they are
in the same cacheline as the _busy counters and not needlessly stored
to in every I/O completion.

With the new model the _busy counters can temporarily go negative,
so all the readers are updated to check for > 0 values.  Longer
term every successful I/O completion will reset the counters to zero,
so the temporarily negative values will not cause any harm.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: default avatarWebb Scales <webbnh@hp.com>
Acked-by: default avatarJens Axboe <axboe@kernel.dk>
Tested-by: default avatarBart Van Assche <bvanassche@acm.org>
Tested-by: default avatarRobert Elliott <elliott@hp.com>
parent 71e75c97

drivers/scsi/scsi.c

+10 −11
Original line number Diff line number Diff line
@@ -727,16 +727,15 @@ void scsi_finish_command(struct scsi_cmnd *cmd) 
	scsi_device_unbusy(sdev);



	/*

         * Clear the flags which say that the device/host is no longer

         * capable of accepting new commands.  These are set in scsi_queue.c

         * for both the queue full condition on a device, and for a

         * host full condition on the host.

	 *

	 * XXX(hch): What about locking?

	 * Clear the flags that say that the device/target/host is no longer

	 * capable of accepting new commands.

	 */

        shost->host_blocked = 0;

	starget->target_blocked = 0;

        sdev->device_blocked = 0;

	if (atomic_read(&shost->host_blocked))

		atomic_set(&shost->host_blocked, 0);

	if (atomic_read(&starget->target_blocked))

		atomic_set(&starget->target_blocked, 0);

	if (atomic_read(&sdev->device_blocked))

		atomic_set(&sdev->device_blocked, 0);



	/*

	 * If we have valid sense information, then some kind of recovery

drivers/scsi/scsi_lib.c

+33 −33
Original line number Diff line number Diff line
@@ -99,14 +99,16 @@ scsi_set_blocked(struct scsi_cmnd *cmd, int reason) 
	 */

	switch (reason) {

	case SCSI_MLQUEUE_HOST_BUSY:

		host->host_blocked = host->max_host_blocked;

		atomic_set(&host->host_blocked, host->max_host_blocked);

		break;

	case SCSI_MLQUEUE_DEVICE_BUSY:

	case SCSI_MLQUEUE_EH_RETRY:

		device->device_blocked = device->max_device_blocked;

		atomic_set(&device->device_blocked,

			   device->max_device_blocked);

		break;

	case SCSI_MLQUEUE_TARGET_BUSY:

		starget->target_blocked = starget->max_target_blocked;

		atomic_set(&starget->target_blocked,

			   starget->max_target_blocked);

		break;

	}

}
@@ -351,29 +353,35 @@ static void scsi_single_lun_run(struct scsi_device *current_sdev) 
	spin_unlock_irqrestore(shost->host_lock, flags);

}



static inline int scsi_device_is_busy(struct scsi_device *sdev)

static inline bool scsi_device_is_busy(struct scsi_device *sdev)

{

	if (atomic_read(&sdev->device_busy) >= sdev->queue_depth ||

	    sdev->device_blocked)

		return 1;

	return 0;

	if (atomic_read(&sdev->device_busy) >= sdev->queue_depth)

		return true;

	if (atomic_read(&sdev->device_blocked) > 0)

		return true;

	return false;

}



static inline int scsi_target_is_busy(struct scsi_target *starget)

static inline bool scsi_target_is_busy(struct scsi_target *starget)

{

	return ((starget->can_queue > 0 &&

		 atomic_read(&starget->target_busy) >= starget->can_queue) ||

		 starget->target_blocked);

	if (starget->can_queue > 0 &&

	    atomic_read(&starget->target_busy) >= starget->can_queue)

		return true;

	if (atomic_read(&starget->target_blocked) > 0)

		return true;

	return false;

}



static inline int scsi_host_is_busy(struct Scsi_Host *shost)

static inline bool scsi_host_is_busy(struct Scsi_Host *shost)

{

	if ((shost->can_queue > 0 &&

	     atomic_read(&shost->host_busy) >= shost->can_queue) ||

	    shost->host_blocked || shost->host_self_blocked)

		return 1;



	return 0;

	if (shost->can_queue > 0 &&

	    atomic_read(&shost->host_busy) >= shost->can_queue)

		return true;

	if (atomic_read(&shost->host_blocked) > 0)

		return true;

	if (shost->host_self_blocked)

		return true;

	return false;

}



static void scsi_starved_list_run(struct Scsi_Host *shost)
@@ -1256,14 +1264,14 @@ static inline int scsi_dev_queue_ready(struct request_queue *q, 
	unsigned int busy;



	busy = atomic_inc_return(&sdev->device_busy) - 1;

	if (sdev->device_blocked) {

	if (atomic_read(&sdev->device_blocked)) {

		if (busy)

			goto out_dec;



		/*

		 * unblock after device_blocked iterates to zero

		 */

		if (--sdev->device_blocked != 0) {

		if (atomic_dec_return(&sdev->device_blocked) > 0) {

			blk_delay_queue(q, SCSI_QUEUE_DELAY);

			goto out_dec;

		}
@@ -1302,19 +1310,15 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost, 
	}



	busy = atomic_inc_return(&starget->target_busy) - 1;

	if (starget->target_blocked) {

	if (atomic_read(&starget->target_blocked) > 0) {

		if (busy)

			goto starved;



		/*

		 * unblock after target_blocked iterates to zero

		 */

		spin_lock_irq(shost->host_lock);

		if (--starget->target_blocked != 0) {

			spin_unlock_irq(shost->host_lock);

		if (atomic_dec_return(&starget->target_blocked) > 0)

			goto out_dec;

		}

		spin_unlock_irq(shost->host_lock);



		SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,

				 "unblocking target at zero depth\n"));
@@ -1349,19 +1353,15 @@ static inline int scsi_host_queue_ready(struct request_queue *q, 
		return 0;



	busy = atomic_inc_return(&shost->host_busy) - 1;

	if (shost->host_blocked) {

	if (atomic_read(&shost->host_blocked) > 0) {

		if (busy)

			goto starved;



		/*

		 * unblock after host_blocked iterates to zero

		 */

		spin_lock_irq(shost->host_lock);

		if (--shost->host_blocked != 0) {

			spin_unlock_irq(shost->host_lock);

		if (atomic_dec_return(&shost->host_blocked) > 0)

			goto out_dec;

		}

		spin_unlock_irq(shost->host_lock);



		SCSI_LOG_MLQUEUE(3,

			shost_printk(KERN_INFO, shost,

drivers/scsi/scsi_sysfs.c

+9 −1
Original line number Diff line number Diff line
@@ -584,7 +584,6 @@ static int scsi_sdev_check_buf_bit(const char *buf) 
/*

 * Create the actual show/store functions and data structures.

 */

sdev_rd_attr (device_blocked, "%d\n");

sdev_rd_attr (type, "%d\n");

sdev_rd_attr (scsi_level, "%d\n");

sdev_rd_attr (vendor, "%.8s\n");
@@ -600,6 +599,15 @@ sdev_show_device_busy(struct device *dev, struct device_attribute *attr, 
}

static DEVICE_ATTR(device_busy, S_IRUGO, sdev_show_device_busy, NULL);



static ssize_t

sdev_show_device_blocked(struct device *dev, struct device_attribute *attr,

		char *buf)

{

	struct scsi_device *sdev = to_scsi_device(dev);

	return snprintf(buf, 20, "%d\n", atomic_read(&sdev->device_blocked));

}

static DEVICE_ATTR(device_blocked, S_IRUGO, sdev_show_device_blocked, NULL);



/*

 * TODO: can we make these symlinks to the block layer ones?

 */

include/scsi/scsi_device.h

+4 −3
Original line number Diff line number Diff line
@@ -82,6 +82,8 @@ struct scsi_device { 
	struct list_head    same_target_siblings; /* just the devices sharing same target id */



	atomic_t device_busy;		/* commands actually active on LLDD */

	atomic_t device_blocked;	/* Device returned QUEUE_FULL. */



	spinlock_t list_lock;

	struct list_head cmd_list;	/* queue of in use SCSI Command structures */

	struct list_head starved_entry;
@@ -180,8 +182,6 @@ struct scsi_device { 
	struct list_head event_list;	/* asserted events */

	struct work_struct event_work;



	unsigned int device_blocked;	/* Device returned QUEUE_FULL. */



	unsigned int max_device_blocked; /* what device_blocked counts down from  */

#define SCSI_DEFAULT_DEVICE_BLOCKED	3
@@ -291,12 +291,13 @@ struct scsi_target { 
						 * the same target will also. */

	/* commands actually active on LLD. */

	atomic_t		target_busy;

	atomic_t		target_blocked;



	/*

	 * LLDs should set this in the slave_alloc host template callout.

	 * If set to zero then there is not limit.

	 */

	unsigned int		can_queue;

	unsigned int		target_blocked;

	unsigned int		max_target_blocked;

#define SCSI_DEFAULT_TARGET_BLOCKED	3

include/scsi/scsi_host.h

+2 −5
Original line number Diff line number Diff line
@@ -583,6 +583,8 @@ struct Scsi_Host { 
	struct blk_queue_tag	*bqt;



	atomic_t host_busy;		   /* commands actually active on low-level */

	atomic_t host_blocked;



	unsigned int host_failed;	   /* commands that failed.

					      protected by host_lock */

	unsigned int host_eh_scheduled;    /* EH scheduled without command */
@@ -681,11 +683,6 @@ struct Scsi_Host { 
	 */

	struct workqueue_struct *tmf_work_q;



	/*

	 * Host has rejected a command because it was busy.

	 */

	unsigned int host_blocked;



	/*

	 * Value host_blocked counts down from

	 */

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