Patch: Revert commit 3e22760d4db6fd89e0be46c3d132390a251da9c6 due to performance issues

[Laurence Oberman <loberman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Hello

This patch reverts commit 3e22760d4db6fd89e0be46c3d132390a251da9c6.

This revert came about because of efforts by Ewan Milne, Curtis Taylor and I.
In researching this issue, significant performance issues were seen on large CPU count 
systems using the software FCOE stack.
Hannes also weighed in.

The same was not apparent on much smaller low count CPU systems.
The behavior introduced by commit 3e22760d4db6fd89e0be46c3d132390a251da9c6 lands sup with large
count CPU systems seeing continual blk_requeue_request() calls due to ML_QUEUE_HOST_BUSY.

>From Ewan:

fc_exch_alloc() used to try all the available exchange managers in the
list for an available exchange id, but this was changed in 2010 so that
if the first matched exchange manager couldn't allocate one, it fails
and we end up returning host busy.  This was due to commit:

Setting the ddp_min module parameter to fcoe to 128MB prevents the ->match
function from permitting the use of the offload exchange manager for the frame,
and we no longer see the problem with host busy status, since it uses the
larger non-offloaded pool.

Reverting commit 3e22760d4db6fd89e0be46c3d132390a251da9c6 was tested to also
prevent the host busy issue due to failing allocations.

Suggested-by: Ewan Milne <emilne-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Suggested-by: Curtis Taylor <cjt-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Tested-by: Laurence Oberman <loberman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Laurence Oberman <loberman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c
index e72673b..d5c4048 100644
--- a/drivers/scsi/libfc/fc_exch.c
+++ b/drivers/scsi/libfc/fc_exch.c
@@ -892,10 +892,15 @@ static inline struct fc_exch *fc_exch_alloc(struct fc_lport *lport,
 					    struct fc_frame *fp)
 {
 	struct fc_exch_mgr_anchor *ema;
+	struct fc_exch *ep;
 
-	list_for_each_entry(ema, &lport->ema_list, ema_list)
-		if (!ema->match || ema->match(fp))
-			return fc_exch_em_alloc(lport, ema->mp);
+	list_for_each_entry(ema, &lport->ema_list, ema_list) {
+		if (!ema->match || ema->match(fp)) {
+			ep = fc_exch_em_alloc(lport, ema->mp);
+			if (ep)
+				return ep;
+		}
+	}
 	return NULL;
 }