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: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
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>
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 1ddf0fb..69da4cb 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -99,14 +99,16 @@
*/
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 @@
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 @@
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 @@
}
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 @@
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,