Commit aedf3497 authored by James Smart's avatar James Smart Committed by James Bottomley

[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

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
  - flush the right workq on delayed work cancel failures.

Large kudos to Michael Reed who has been working this issue for the last
Signed-off-by: default avatarJames Bottomley <>
parent b0d23648
This diff is collapsed.
......@@ -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 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: */
/* 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) {
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;
result = DID_NO_CONNECT << 16;
result = DID_BUS_BUSY << 16;
result = DID_IMM_RETRY << 16;
result = DID_NO_CONNECT << 16;
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