firewire: fw-sbp2: use an own workqueue (fix system responsiveness)

Firewire-sbp2 did very uncooperative things in the kernel's shared
workqueue:  Sleeping until reception of management status from the
target for up to 2 seconds, and performing SCSI inquiry and all of the
setup of SCSI command set drivers via scsi_add_device.  If there were
transient or permanent error conditions, this caused long blockage of
the kernel's events process, noticeable e.g. by blocked keyboard input.

We now allocate a workqueue process exclusive to fw-sbp2.  As a side
effect, this also increases parallelism of fw-sbp2's login and reconnect
work versus fw-core's device discovery and device update work which is
performed in the shared workqueue.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Kristian Høgsberg <krh@redhat.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/drivers/firewire/fw-sbp2.c b/drivers/firewire/fw-sbp2.c
index f96f19293dd..5596df65c8e 100644
--- a/drivers/firewire/fw-sbp2.c
+++ b/drivers/firewire/fw-sbp2.c
@@ -39,6 +39,7 @@
 #include <linux/string.h>
 #include <linux/stringify.h>
 #include <linux/timer.h>
+#include <linux/workqueue.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>
@@ -625,6 +626,8 @@ static void sbp2_release_target(struct kref *kref)
         scsi_host_put(shost);
 }
 
+static struct workqueue_struct *sbp2_wq;
+
 static void sbp2_reconnect(struct work_struct *work);
 
 static void sbp2_login(struct work_struct *work)
@@ -647,7 +650,8 @@ static void sbp2_login(struct work_struct *work)
         if (sbp2_send_management_orb(lu, node_id, generation,
                                 SBP2_LOGIN_REQUEST, lu->lun, &response) < 0) {
                 if (lu->retries++ < 5) {
-                        schedule_delayed_work(&lu->work, DIV_ROUND_UP(HZ, 5));
+                        queue_delayed_work(sbp2_wq, &lu->work,
+                                           DIV_ROUND_UP(HZ, 5));
                 } else {
                         fw_error("failed to login to %s LUN %04x\n",
                                  unit->device.bus_id, lu->lun);
@@ -866,7 +870,7 @@ static int sbp2_probe(struct device *dev)
          * work.
          */
         list_for_each_entry(lu, &tgt->lu_list, link)
-                if (schedule_delayed_work(&lu->work, 0))
+                if (queue_delayed_work(sbp2_wq, &lu->work, 0))
                         kref_get(&tgt->kref);
         return 0;
 
@@ -910,7 +914,7 @@ static void sbp2_reconnect(struct work_struct *work)
                         lu->retries = 0;
                         PREPARE_DELAYED_WORK(&lu->work, sbp2_login);
                 }
-                schedule_delayed_work(&lu->work, DIV_ROUND_UP(HZ, 5));
+                queue_delayed_work(sbp2_wq, &lu->work, DIV_ROUND_UP(HZ, 5));
                 return;
         }
 
@@ -940,7 +944,7 @@ static void sbp2_update(struct fw_unit *unit)
          */
         list_for_each_entry(lu, &tgt->lu_list, link) {
                 lu->retries = 0;
-                if (schedule_delayed_work(&lu->work, 0))
+                if (queue_delayed_work(sbp2_wq, &lu->work, 0))
                         kref_get(&tgt->kref);
         }
 }
@@ -1335,12 +1339,17 @@ MODULE_ALIAS("sbp2");
 
 static int __init sbp2_init(void)
 {
+        sbp2_wq = create_singlethread_workqueue(KBUILD_MODNAME);
+        if (!sbp2_wq)
+                return -ENOMEM;
+
         return driver_register(&sbp2_driver.driver);
 }
 
 static void __exit sbp2_cleanup(void)
 {
         driver_unregister(&sbp2_driver.driver);
+        destroy_workqueue(sbp2_wq);
 }
 
 module_init(sbp2_init);