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>

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 5f36788705ba..de57b8bca7be 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -334,7 +334,6 @@ store_shost_eh_deadline(struct device *dev, struct device_attribute *attr,
 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");
@@ -344,6 +343,14 @@ 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,
         &dev_attr_host_busy.attr,