[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>

7 files changed, 83 insertions, 62 deletions

diff --git a/drivers/scsi/libsas/sas_discover.c b/drivers/scsi/libsas/sas_discover.c
index 364679675602..c7ac88288bf1 100644
--- a/drivers/scsi/libsas/sas_discover.c
+++ b/drivers/scsi/libsas/sas_discover.c
@@ -205,8 +205,7 @@ void sas_notify_lldd_dev_gone(struct domain_device *dev)
 static void sas_probe_devices(struct work_struct *work)
 {
         struct domain_device *dev, *n;
-        struct sas_discovery_event *ev =
-                container_of(work, struct sas_discovery_event, work);
+        struct sas_discovery_event *ev = to_sas_discovery_event(work);
         struct asd_sas_port *port = ev->port;
 
         clear_bit(DISCE_PROBE, &port->disc.pending);
@@ -291,8 +290,7 @@ static void sas_unregister_common_dev(struct asd_sas_port *port, struct domain_d
 static void sas_destruct_devices(struct work_struct *work)
 {
         struct domain_device *dev, *n;
-        struct sas_discovery_event *ev =
-                container_of(work, struct sas_discovery_event, work);
+        struct sas_discovery_event *ev = to_sas_discovery_event(work);
         struct asd_sas_port *port = ev->port;
 
         clear_bit(DISCE_DESTRUCT, &port->disc.pending);
@@ -377,8 +375,7 @@ static void sas_discover_domain(struct work_struct *work)
 {
         struct domain_device *dev;
         int error = 0;
-        struct sas_discovery_event *ev =
-                container_of(work, struct sas_discovery_event, work);
+        struct sas_discovery_event *ev = to_sas_discovery_event(work);
         struct asd_sas_port *port = ev->port;
 
         clear_bit(DISCE_DISCOVER_DOMAIN, &port->disc.pending);
@@ -437,8 +434,7 @@ static void sas_discover_domain(struct work_struct *work)
 static void sas_revalidate_domain(struct work_struct *work)
 {
         int res = 0;
-        struct sas_discovery_event *ev =
-                container_of(work, struct sas_discovery_event, work);
+        struct sas_discovery_event *ev = to_sas_discovery_event(work);
         struct asd_sas_port *port = ev->port;
         struct sas_ha_struct *ha = port->ha;
 
@@ -466,21 +462,25 @@ static void sas_revalidate_domain(struct work_struct *work)
 
 /* ---------- Events ---------- */
 
-static void sas_chain_work(struct sas_ha_struct *ha, struct work_struct *work)
+static void sas_chain_work(struct sas_ha_struct *ha, struct sas_work *sw)
 {
-        /* chained work is not subject to SA_HA_DRAINING or SAS_HA_REGISTERED */
-        scsi_queue_work(ha->core.shost, work);
+        /* chained work is not subject to SA_HA_DRAINING or
+         * SAS_HA_REGISTERED, because it is either submitted in the
+         * workqueue, or known to be submitted from a context that is
+         * not racing against draining
+         */
+        scsi_queue_work(ha->core.shost, &sw->work);
 }
 
 static void sas_chain_event(int event, unsigned long *pending,
-                            struct work_struct *work,
+                            struct sas_work *sw,
                             struct sas_ha_struct *ha)
 {
         if (!test_and_set_bit(event, pending)) {
                 unsigned long flags;
 
                 spin_lock_irqsave(&ha->state_lock, flags);
-                sas_chain_work(ha, work);
+                sas_chain_work(ha, sw);
                 spin_unlock_irqrestore(&ha->state_lock, flags);
         }
 }
@@ -519,7 +519,7 @@ void sas_init_disc(struct sas_discovery *disc, struct asd_sas_port *port)
 
         disc->pending = 0;
         for (i = 0; i < DISC_NUM_EVENTS; i++) {
-                INIT_WORK(&disc->disc_work[i].work, sas_event_fns[i]);
+                INIT_SAS_WORK(&disc->disc_work[i].work, sas_event_fns[i]);
                 disc->disc_work[i].port = port;
         }
 }
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;
         }
 
diff --git a/drivers/scsi/libsas/sas_init.c b/drivers/scsi/libsas/sas_init.c
index 120bff64be30..10cb5ae30977 100644
--- a/drivers/scsi/libsas/sas_init.c
+++ b/drivers/scsi/libsas/sas_init.c
@@ -94,8 +94,7 @@ void sas_hash_addr(u8 *hashed, const u8 *sas_addr)
 
 void sas_hae_reset(struct work_struct *work)
 {
-        struct sas_ha_event *ev =
-                container_of(work, struct sas_ha_event, work);
+        struct sas_ha_event *ev = to_sas_ha_event(work);
         struct sas_ha_struct *ha = ev->ha;
 
         clear_bit(HAE_RESET, &ha->pending);
@@ -369,14 +368,14 @@ static void sas_phy_release(struct sas_phy *phy)
 
 static void phy_reset_work(struct work_struct *work)
 {
-        struct sas_phy_data *d = container_of(work, typeof(*d), reset_work);
+        struct sas_phy_data *d = container_of(work, typeof(*d), reset_work.work);
 
         d->reset_result = transport_sas_phy_reset(d->phy, d->hard_reset);
 }
 
 static void phy_enable_work(struct work_struct *work)
 {
-        struct sas_phy_data *d = container_of(work, typeof(*d), enable_work);
+        struct sas_phy_data *d = container_of(work, typeof(*d), enable_work.work);
 
         d->enable_result = sas_phy_enable(d->phy, d->enable);
 }
@@ -389,8 +388,8 @@ static int sas_phy_setup(struct sas_phy *phy)
                 return -ENOMEM;
 
         mutex_init(&d->event_lock);
-        INIT_WORK(&d->reset_work, phy_reset_work);
-        INIT_WORK(&d->enable_work, phy_enable_work);
+        INIT_SAS_WORK(&d->reset_work, phy_reset_work);
+        INIT_SAS_WORK(&d->enable_work, phy_enable_work);
         d->phy = phy;
         phy->hostdata = d;
 
diff --git a/drivers/scsi/libsas/sas_internal.h b/drivers/scsi/libsas/sas_internal.h
index f05c63879949..507e4cf12e56 100644
--- a/drivers/scsi/libsas/sas_internal.h
+++ b/drivers/scsi/libsas/sas_internal.h
@@ -45,10 +45,10 @@ struct sas_phy_data {
         struct mutex event_lock;
         int hard_reset;
         int reset_result;
-        struct work_struct reset_work;
+        struct sas_work reset_work;
         int enable;
         int enable_result;
-        struct work_struct enable_work;
+        struct sas_work enable_work;
 };
 
 void sas_scsi_recover_host(struct Scsi_Host *shost);
@@ -80,7 +80,7 @@ void sas_porte_broadcast_rcvd(struct work_struct *work);
 void sas_porte_link_reset_err(struct work_struct *work);
 void sas_porte_timer_event(struct work_struct *work);
 void sas_porte_hard_reset(struct work_struct *work);
-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);
 
 int sas_notify_lldd_dev_found(struct domain_device *);
 void sas_notify_lldd_dev_gone(struct domain_device *);
diff --git a/drivers/scsi/libsas/sas_phy.c b/drivers/scsi/libsas/sas_phy.c
index dcfd4a9105c5..521422e857ab 100644
--- a/drivers/scsi/libsas/sas_phy.c
+++ b/drivers/scsi/libsas/sas_phy.c
@@ -32,8 +32,7 @@
 
 static void sas_phye_loss_of_signal(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
 
         clear_bit(PHYE_LOSS_OF_SIGNAL, &phy->phy_events_pending);
@@ -43,8 +42,7 @@ static void sas_phye_loss_of_signal(struct work_struct *work)
 
 static void sas_phye_oob_done(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
 
         clear_bit(PHYE_OOB_DONE, &phy->phy_events_pending);
@@ -53,8 +51,7 @@ static void sas_phye_oob_done(struct work_struct *work)
 
 static void sas_phye_oob_error(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
         struct sas_ha_struct *sas_ha = phy->ha;
         struct asd_sas_port *port = phy->port;
@@ -85,8 +82,7 @@ static void sas_phye_oob_error(struct work_struct *work)
 
 static void sas_phye_spinup_hold(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
         struct sas_ha_struct *sas_ha = phy->ha;
         struct sas_internal *i =
@@ -127,14 +123,12 @@ int sas_register_phys(struct sas_ha_struct *sas_ha)
                 phy->error = 0;
                 INIT_LIST_HEAD(&phy->port_phy_el);
                 for (k = 0; k < PORT_NUM_EVENTS; k++) {
-                        INIT_WORK(&phy->port_events[k].work,
-                                  sas_port_event_fns[k]);
+                        INIT_SAS_WORK(&phy->port_events[k].work, sas_port_event_fns[k]);
                         phy->port_events[k].phy = phy;
                 }
 
                 for (k = 0; k < PHY_NUM_EVENTS; k++) {
-                        INIT_WORK(&phy->phy_events[k].work,
-                                  sas_phy_event_fns[k]);
+                        INIT_SAS_WORK(&phy->phy_events[k].work, sas_phy_event_fns[k]);
                         phy->phy_events[k].phy = phy;
                 }
 
@@ -144,8 +138,7 @@ int sas_register_phys(struct sas_ha_struct *sas_ha)
                 spin_lock_init(&phy->sas_prim_lock);
                 phy->frame_rcvd_size = 0;
 
-                phy->phy = sas_phy_alloc(&sas_ha->core.shost->shost_gendev,
-                                         i);
+                phy->phy = sas_phy_alloc(&sas_ha->core.shost->shost_gendev, i);
                 if (!phy->phy)
                         return -ENOMEM;
 
diff --git a/drivers/scsi/libsas/sas_port.c b/drivers/scsi/libsas/sas_port.c
index eb19c016d500..1cf7d75ad5eb 100644
--- a/drivers/scsi/libsas/sas_port.c
+++ b/drivers/scsi/libsas/sas_port.c
@@ -208,8 +208,7 @@ void sas_deform_port(struct asd_sas_phy *phy, int gone)
 
 void sas_porte_bytes_dmaed(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
 
         clear_bit(PORTE_BYTES_DMAED, &phy->port_events_pending);
@@ -219,8 +218,7 @@ void sas_porte_bytes_dmaed(struct work_struct *work)
 
 void sas_porte_broadcast_rcvd(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
         unsigned long flags;
         u32 prim;
@@ -237,8 +235,7 @@ void sas_porte_broadcast_rcvd(struct work_struct *work)
 
 void sas_porte_link_reset_err(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
 
         clear_bit(PORTE_LINK_RESET_ERR, &phy->port_events_pending);
@@ -248,8 +245,7 @@ void sas_porte_link_reset_err(struct work_struct *work)
 
 void sas_porte_timer_event(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
 
         clear_bit(PORTE_TIMER_EVENT, &phy->port_events_pending);
@@ -259,8 +255,7 @@ void sas_porte_timer_event(struct work_struct *work)
 
 void sas_porte_hard_reset(struct work_struct *work)
 {
-        struct asd_sas_event *ev =
-                container_of(work, struct asd_sas_event, work);
+        struct asd_sas_event *ev = to_asd_sas_event(work);
         struct asd_sas_phy *phy = ev->phy;
 
         clear_bit(PORTE_HARD_RESET, &phy->port_events_pending);
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,