[SCSI] libsas: introduce sas_work to fix sas_drain_work vs sas_queue_work

When requeuing work to a draining workqueue the last work instance may
not be idle, so sas_queue_work() must not touch work->entry.  Introduce
sas_work with a drain_node list_head to have a private list for
collecting work deferred due to drain collision.

Fixes reports like:
  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: [<ffffffff810410d4>] process_one_work+0x2e/0x338

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 13 insertions, 11 deletions

diff --git a/drivers/scsi/libsas/sas_event.c b/drivers/scsi/libsas/sas_event.c
index 16639bbae629..4e4292d210c1 100644
--- a/drivers/scsi/libsas/sas_event.c
+++ b/drivers/scsi/libsas/sas_event.c
@@ -27,19 +27,21 @@
 #include "sas_internal.h"
 #include "sas_dump.h"
 
-void sas_queue_work(struct sas_ha_struct *ha, struct work_struct *work)
+void sas_queue_work(struct sas_ha_struct *ha, struct sas_work *sw)
 {
         if (!test_bit(SAS_HA_REGISTERED, &ha->state))
                 return;
 
-        if (test_bit(SAS_HA_DRAINING, &ha->state))
-                list_add(&work->entry, &ha->defer_q);
-        else
-                scsi_queue_work(ha->core.shost, work);
+        if (test_bit(SAS_HA_DRAINING, &ha->state)) {
+                /* add it to the defer list, if not already pending */
+                if (list_empty(&sw->drain_node))
+                        list_add(&sw->drain_node, &ha->defer_q);
+        } else
+                scsi_queue_work(ha->core.shost, &sw->work);
 }
 
 static void sas_queue_event(int event, unsigned long *pending,
-                            struct work_struct *work,
+                            struct sas_work *work,
                             struct sas_ha_struct *ha)
 {
         if (!test_and_set_bit(event, pending)) {
@@ -55,7 +57,7 @@ static void sas_queue_event(int event, unsigned long *pending,
 void __sas_drain_work(struct sas_ha_struct *ha)
 {
         struct workqueue_struct *wq = ha->core.shost->work_q;
-        struct work_struct *w, *_w;
+        struct sas_work *sw, *_sw;
 
         set_bit(SAS_HA_DRAINING, &ha->state);
         /* flush submitters */
@@ -66,9 +68,9 @@ void __sas_drain_work(struct sas_ha_struct *ha)
 
         spin_lock_irq(&ha->state_lock);
         clear_bit(SAS_HA_DRAINING, &ha->state);
-        list_for_each_entry_safe(w, _w, &ha->defer_q, entry) {
-                list_del_init(&w->entry);
-                sas_queue_work(ha, w);
+        list_for_each_entry_safe(sw, _sw, &ha->defer_q, drain_node) {
+                list_del_init(&sw->drain_node);
+                sas_queue_work(ha, sw);
         }
         spin_unlock_irq(&ha->state_lock);
 }
@@ -151,7 +153,7 @@ int sas_init_events(struct sas_ha_struct *sas_ha)
         int i;
 
         for (i = 0; i < HA_NUM_EVENTS; i++) {
-                INIT_WORK(&sas_ha->ha_events[i].work, sas_ha_event_fns[i]);
+                INIT_SAS_WORK(&sas_ha->ha_events[i].work, sas_ha_event_fns[i]);
                 sas_ha->ha_events[i].ha = sas_ha;
         }