[SCSI] FC transport: fixes for workq deadlocks

As previously reported via Michael Reed, the FC transport took a hit
in 2.6.15 (perhaps a little earlier) when we solved a recursion error.
There are 2 deadlocks occurring:
- With scan and the delete items sharing the same workq, flushing the
  workq for the delete code was getting it stalled behind a very long
  running scan code path.
- There's a deadlock where scsi_remove_target() has to sit behind
  scsi_scan_target() due to contention over the scan_lock().

This patch resolves the 1st deadlock and significantly reduces the
odds of the second. So far, we have only replicated the 2nd deadlock
on a highly-parallel SMP system. More on the 2nd deadlock in a following
email.

This patch reworks the transport to:
- Only use the scsi host workq for scanning
- Use 2 other workq's internally. One for deletions, the other for
  scheduled deletions. Originally, we tried this with a single workq,
  but the occassional flushes of the scheduled queues was hitting the
  second deadlock with a slightly higher frequency. In the future, we'll
  look at the LLDD's and the transport to see if we can get rid of this
  extra overhead.
- When moving to the other workq's we tightened up some object states
  and some lock handling.
- Properly syncs adds/deletes
- minor code cleanups
  - directly reference fc_host_attrs, rather than through attribute
    macros
  - flush the right workq on delayed work cancel failures.

Large kudos to Michael Reed who has been working this issue for the last
month.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

1 files changed, 30 insertions, 11 deletions

diff --git a/include/scsi/scsi_transport_fc.h b/include/scsi/scsi_transport_fc.h
index cf3fec8be1e3..5626225bd3ae 100644
--- a/include/scsi/scsi_transport_fc.h
+++ b/include/scsi/scsi_transport_fc.h
@@ -202,12 +202,19 @@ struct fc_rport {	/* aka fc_starget_attrs */
         /* internal data */
         unsigned int channel;
         u32 number;
+        u8 flags;
         struct list_head peers;
         struct device dev;
         struct work_struct dev_loss_work;
         struct work_struct scan_work;
+        struct work_struct stgt_delete_work;
+        struct work_struct rport_delete_work;
 } __attribute__((aligned(sizeof(unsigned long))));
 
+/* bit field values for struct fc_rport "flags" field: */
+#define FC_RPORT_DEVLOSS_PENDING        0x01
+#define FC_RPORT_SCAN_PENDING           0x02
+
 #define dev_to_rport(d)                         \
         container_of(d, struct fc_rport, dev)
 #define transport_class_to_rport(classdev)      \
@@ -327,13 +334,16 @@ struct fc_host_attrs {
         struct list_head rport_bindings;
         u32 next_rport_number;
         u32 next_target_id;
-        u8 flags;
-        struct work_struct rport_del_work;
-};
 
-/* values for struct fc_host_attrs "flags" field: */
-#define FC_SHOST_RPORT_DEL_SCHEDULED    0x01
+        /* work queues for rport state manipulation */
+        char work_q_name[KOBJ_NAME_LEN];
+        struct workqueue_struct *work_q;
+        char devloss_work_q_name[KOBJ_NAME_LEN];
+        struct workqueue_struct *devloss_work_q;
+};
 
+#define shost_to_fc_host(x) \
+        ((struct fc_host_attrs *)(x)->shost_data)
 
 #define fc_host_node_name(x) \
         (((struct fc_host_attrs *)(x)->shost_data)->node_name)
@@ -375,10 +385,14 @@ struct fc_host_attrs {
         (((struct fc_host_attrs *)(x)->shost_data)->next_rport_number)
 #define fc_host_next_target_id(x) \
         (((struct fc_host_attrs *)(x)->shost_data)->next_target_id)
-#define fc_host_flags(x) \
-        (((struct fc_host_attrs *)(x)->shost_data)->flags)
-#define fc_host_rport_del_work(x) \
-        (((struct fc_host_attrs *)(x)->shost_data)->rport_del_work)
+#define fc_host_work_q_name(x) \
+        (((struct fc_host_attrs *)(x)->shost_data)->work_q_name)
+#define fc_host_work_q(x) \
+        (((struct fc_host_attrs *)(x)->shost_data)->work_q)
+#define fc_host_devloss_work_q_name(x) \
+        (((struct fc_host_attrs *)(x)->shost_data)->devloss_work_q_name)
+#define fc_host_devloss_work_q(x) \
+        (((struct fc_host_attrs *)(x)->shost_data)->devloss_work_q)
 
 
 /* The functions by which the transport class and the driver communicate */
@@ -461,10 +475,15 @@ fc_remote_port_chkready(struct fc_rport *rport)
 
         switch (rport->port_state) {
         case FC_PORTSTATE_ONLINE:
-                result = 0;
+                if (rport->roles & FC_RPORT_ROLE_FCP_TARGET)
+                        result = 0;
+                else if (rport->flags & FC_RPORT_DEVLOSS_PENDING)
+                        result = DID_IMM_RETRY << 16;
+                else
+                        result = DID_NO_CONNECT << 16;
                 break;
         case FC_PORTSTATE_BLOCKED:
-                result = DID_BUS_BUSY << 16;
+                result = DID_IMM_RETRY << 16;
                 break;
         default:
                 result = DID_NO_CONNECT << 16;