[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, 36 insertions, 4 deletions

diff --git a/include/scsi/libsas.h b/include/scsi/libsas.h
index 5f5ed1b8b41b..f4f1c96dca72 100644
--- a/include/scsi/libsas.h
+++ b/include/scsi/libsas.h
@@ -217,11 +217,29 @@ struct domain_device {
         struct kref kref;
 };
 
-struct sas_discovery_event {
+struct sas_work {
+        struct list_head drain_node;
         struct work_struct work;
+};
+
+static inline void INIT_SAS_WORK(struct sas_work *sw, void (*fn)(struct work_struct *))
+{
+        INIT_WORK(&sw->work, fn);
+        INIT_LIST_HEAD(&sw->drain_node);
+}
+
+struct sas_discovery_event {
+        struct sas_work work;
         struct asd_sas_port *port;
 };
 
+static inline struct sas_discovery_event *to_sas_discovery_event(struct work_struct *work)
+{
+        struct sas_discovery_event *ev = container_of(work, typeof(*ev), work.work);
+
+        return ev;
+}
+
 struct sas_discovery {
         struct sas_discovery_event disc_work[DISC_NUM_EVENTS];
         unsigned long    pending;
@@ -244,7 +262,7 @@ struct asd_sas_port {
         struct list_head destroy_list;
         enum   sas_linkrate linkrate;
 
-        struct work_struct work;
+        struct sas_work work;
 
 /* public: */
         int id;
@@ -270,10 +288,17 @@ struct asd_sas_port {
 };
 
 struct asd_sas_event {
-        struct work_struct work;
+        struct sas_work work;
         struct asd_sas_phy *phy;
 };
 
+static inline struct asd_sas_event *to_asd_sas_event(struct work_struct *work)
+{
+        struct asd_sas_event *ev = container_of(work, typeof(*ev), work.work);
+
+        return ev;
+}
+
 /* The phy pretty much is controlled by the LLDD.
  * The class only reads those fields.
  */
@@ -333,10 +358,17 @@ struct scsi_core {
 };
 
 struct sas_ha_event {
-        struct work_struct work;
+        struct sas_work work;
         struct sas_ha_struct *ha;
 };
 
+static inline struct sas_ha_event *to_sas_ha_event(struct work_struct *work)
+{
+        struct sas_ha_event *ev = container_of(work, typeof(*ev), work.work);
+
+        return ev;
+}
+
 enum sas_ha_state {
         SAS_HA_REGISTERED,
         SAS_HA_DRAINING,