[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>
diff --git a/include/scsi/scsi_transport_fc.h b/include/scsi/scsi_transport_fc.h
index cf3fec8..5626225 100644
--- a/include/scsi/scsi_transport_fc.h
+++ b/include/scsi/scsi_transport_fc.h
@@ -202,12 +202,19 @@
/* 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 list_head rport_bindings;
u32 next_rport_number;
u32 next_target_id;
- u8 flags;
- struct work_struct rport_del_work;
+
+ /* 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;
};
-/* values for struct fc_host_attrs "flags" field: */
-#define FC_SHOST_RPORT_DEL_SCHEDULED 0x01
-
+#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 *)(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 @@
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;