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Subject[PATCH 09/14] scsi: fix the {host,target,device}_blocked counter mess
Date
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>
---
drivers/scsi/scsi.c | 21 ++++++------
drivers/scsi/scsi_lib.c | 82 +++++++++++++++++++++-----------------------
drivers/scsi/scsi_sysfs.c | 10 +++++-
include/scsi/scsi_device.h | 7 ++--
include/scsi/scsi_host.h | 7 ++--
5 files changed, 64 insertions(+), 63 deletions(-)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 35a23e2..b362058 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -729,17 +729,16 @@ 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?
- */
- shost->host_blocked = 0;
- starget->target_blocked = 0;
- sdev->device_blocked = 0;
+ /*
+ * Clear the flags which say that the device/target/host is no longer
+ * capable of accepting new commands.
+ */
+ 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
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e23fef5..a39d5ba 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -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;
}
}
@@ -351,30 +353,39 @@ 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)
- return 1;
- if (sdev->device_blocked)
- return 1;
+ return true;
+ if (atomic_read(&sdev->device_blocked) > 0)
+ return true;
return 0;
}

-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) {
+ if (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;
+ if (shost->can_queue > 0) {
+ if (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 0;
+ return false;
}

static void scsi_starved_list_run(struct Scsi_Host *shost)
@@ -1283,11 +1294,8 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
unsigned int busy;

busy = atomic_inc_return(&sdev->device_busy) - 1;
- if (busy == 0 && sdev->device_blocked) {
- /*
- * unblock after device_blocked iterates to zero
- */
- if (--sdev->device_blocked != 0) {
+ if (busy == 0 && atomic_read(&sdev->device_blocked) > 0) {
+ if (atomic_dec_return(&sdev->device_blocked) > 0) {
blk_delay_queue(q, SCSI_QUEUE_DELAY);
goto out_dec;
}
@@ -1297,7 +1305,7 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,

if (busy >= sdev->queue_depth)
goto out_dec;
- if (sdev->device_blocked)
+ if (atomic_read(&sdev->device_blocked) > 0)
goto out_dec;

return 1;
@@ -1328,16 +1336,9 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
}

busy = atomic_inc_return(&starget->target_busy) - 1;
- if (busy == 0 && starget->target_blocked) {
- /*
- * 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 (busy == 0 && atomic_read(&starget->target_blocked) > 0) {
+ 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"));
@@ -1345,7 +1346,7 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,

if (starget->can_queue > 0 && busy >= starget->can_queue)
goto starved;
- if (starget->target_blocked)
+ if (atomic_read(&starget->target_blocked) > 0)
goto starved;

return 1;
@@ -1374,16 +1375,9 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
return 0;

busy = atomic_inc_return(&shost->host_busy) - 1;
- if (busy == 0 && shost->host_blocked) {
- /*
- * 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 (busy == 0 && atomic_read(&shost->host_blocked) > 0) {
+ 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,
@@ -1392,7 +1386,9 @@ static inline int scsi_host_queue_ready(struct request_queue *q,

if (shost->can_queue > 0 && busy >= shost->can_queue)
goto starved;
- if (shost->host_blocked || shost->host_self_blocked)
+ if (atomic_read(&shost->host_blocked) > 0)
+ goto starved;
+ if (shost->host_self_blocked)
goto starved;

/* We're OK to process the command, so we can't be starved */
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 54e3dac..deef063 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -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?
*/
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 5ff3d24..a8a8981 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -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;
@@ -179,8 +181,6 @@ 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

@@ -290,12 +290,13 @@ 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

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 3d124f7..7f9bbda 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -604,6 +604,8 @@ 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 */
@@ -703,11 +705,6 @@ 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
*/
unsigned int max_host_blocked;
--
1.7.10.4


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