The patch titled
fc transport: resolve scan vs delete deadlocks
has been added to the -mm tree. Its filename is
fc-transport-resolve-scan-vs-delete-deadlocks.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: fc transport: resolve scan vs delete deadlocks
From: James Smart <James.Smart@xxxxxxxxxx>
In a prior posting to linux-scsi on the fc transport and workq
deadlocks, we noted a second error that did not have a patch:
http://marc.theaimsgroup.com/?l=linux-scsi&m=114467847711383&w=2
- There's a deadlock where scsi_remove_target() has to sit behind
scsi_scan_target() due to contention over the scan_lock().
Subsequently we posted a request for comments about the deadlock:
http://marc.theaimsgroup.com/?l=linux-scsi&m=114469358829500&w=2
This posting resolves the second error. Here's what we now understand,
and are implementing:
If the lldd deletes the rport while a scan is active, the sdev's queue
is blocked which stops the issuing of commands associated with the scan.
At this point, the scan stalls, and does so with the shost->scan_mutex held.
If, at this point, if any scan or delete request is made on the host, it
will stall waiting for the scan_mutex.
For the FC transport, we queue all delete work to a single workq.
So, things worked fine when competing with the scan, as long as the
target blocking the scan was the same target at the top of our delete
workq, as the delete workq routine always unblocked just prior to
requesting the delete. Unfortunately, if the top of our delete workq
was for a different target, we deadlock. Additionally, if the target
blocking scan returned, we were unblocking it in the scan workq routine,
which really won't execute until the existing stalled scan workq
completes (e.g. we're re-scheduling it while it is in the midst of its
execution).
This patch moves the unblock out of the workq routines and moves it to
the context that is scheduling the work. This ensures that at some point,
we will unblock the target that is blocking scan. Please note, however,
that the deadlock condition may still occur while it waits for the
transport to timeout an unblock on a target. Worst case, this is bounded
by the transport dev_loss_tmo (default: 30 seconds).
Finally, Michael Reed deserves the credit for the bulk of this patch,
analysis, and it's testing. Thank you for your help.
Note: The request for comments statements about the gross-ness of the
scan_mutex still stand.
Signed-off-by: Michael Reed <mdr@xxxxxxx>
Signed-off-by: James Smart <james.smart@xxxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
drivers/scsi/scsi_transport_fc.c | 28 +++++++++++++++-------------
1 files changed, 15 insertions(+), 13 deletions(-)
diff -puN drivers/scsi/scsi_transport_fc.c~fc-transport-resolve-scan-vs-delete-deadlocks drivers/scsi/scsi_transport_fc.c
--- 25/drivers/scsi/scsi_transport_fc.c~fc-transport-resolve-scan-vs-delete-deadlocks Tue Jun 27 14:45:21 2006
+++ 25-akpm/drivers/scsi/scsi_transport_fc.c Tue Jun 27 14:45:21 2006
@@ -1284,7 +1284,9 @@ EXPORT_SYMBOL(fc_release_transport);
* @work: Work to queue for execution.
*
* Return value:
- * 0 on success / != 0 for error
+ * 1 - work queued for execution
+ * 0 - work is already queued
+ * -EINVAL - work queue doesn't exist
**/
static int
fc_queue_work(struct Scsi_Host *shost, struct work_struct *work)
@@ -1434,8 +1436,6 @@ fc_starget_delete(void *data)
struct Scsi_Host *shost = rport_to_shost(rport);
unsigned long flags;
- scsi_target_unblock(&rport->dev);
-
spin_lock_irqsave(shost->host_lock, flags);
if (rport->flags & FC_RPORT_DEVLOSS_PENDING) {
spin_unlock_irqrestore(shost->host_lock, flags);
@@ -1707,6 +1707,8 @@ fc_remote_port_add(struct Scsi_Host *sho
spin_unlock_irqrestore(shost->host_lock, flags);
+ scsi_target_unblock(&rport->dev);
+
return rport;
}
}
@@ -1762,9 +1764,10 @@ fc_remote_port_add(struct Scsi_Host *sho
/* initiate a scan of the target */
rport->flags |= FC_RPORT_SCAN_PENDING;
scsi_queue_work(shost, &rport->scan_work);
- }
-
- spin_unlock_irqrestore(shost->host_lock, flags);
+ spin_unlock_irqrestore(shost->host_lock, flags);
+ scsi_target_unblock(&rport->dev);
+ } else
+ spin_unlock_irqrestore(shost->host_lock, flags);
return rport;
}
@@ -1938,6 +1941,7 @@ fc_remote_port_rolechg(struct fc_rport
rport->flags |= FC_RPORT_SCAN_PENDING;
scsi_queue_work(shost, &rport->scan_work);
spin_unlock_irqrestore(shost->host_lock, flags);
+ scsi_target_unblock(&rport->dev);
}
}
EXPORT_SYMBOL(fc_remote_port_rolechg);
@@ -1970,8 +1974,9 @@ fc_timeout_deleted_rport(void *data)
dev_printk(KERN_ERR, &rport->dev,
"blocked FC remote port time out: no longer"
" a FCP target, removing starget\n");
- fc_queue_work(shost, &rport->stgt_delete_work);
spin_unlock_irqrestore(shost->host_lock, flags);
+ scsi_target_unblock(&rport->dev);
+ fc_queue_work(shost, &rport->stgt_delete_work);
return;
}
@@ -2035,17 +2040,15 @@ fc_timeout_deleted_rport(void *data)
* went away and didn't come back - we'll remove
* all attached scsi devices.
*/
- fc_queue_work(shost, &rport->stgt_delete_work);
-
spin_unlock_irqrestore(shost->host_lock, flags);
+
+ scsi_target_unblock(&rport->dev);
+ fc_queue_work(shost, &rport->stgt_delete_work);
}
/**
* fc_scsi_scan_rport - called to perform a scsi scan on a remote port.
*
- * Will unblock the target (in case it went away and has now come back),
- * then invoke a scan.
- *
* @data: remote port to be scanned.
**/
static void
@@ -2057,7 +2060,6 @@ fc_scsi_scan_rport(void *data)
if ((rport->port_state == FC_PORTSTATE_ONLINE) &&
(rport->roles & FC_RPORT_ROLE_FCP_TARGET)) {
- scsi_target_unblock(&rport->dev);
scsi_scan_target(&rport->dev, rport->channel,
rport->scsi_target_id, SCAN_WILD_CARD, 1);
}
_
Patches currently in -mm which might be from James.Smart@xxxxxxxxxx are
git-scsi-misc.patch
fc-transport-bug-fix-correct-references.patch
scsi-midlayer-fix-sdev-reuse-after-free.patch
block-i-o-while-sg-reset-operation-in-progress-midlayer.patch
block-i-o-while-sg-reset-operation-in-progress-lpfc.patch
fc-transport-resolve-scan-vs-delete-deadlocks.patch
-
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