This patch introduces the mechanism to recover from I/O failures by re-initializing the path if the device is running on only one path.
Problem: Device mapper fails the path for every I/O error. It does not care about the type of error. There are certain errors which can be recovered by re-initializing the path again. I have seen this problem during my testing on rdac device handler. I have observed I/O errors when there is a change in Lun ownership. When Lun ownership changes device will return back with check condition with sense 0x05/0x94/0x01(SK/ASC/ASCQ -meaning Lun ownership changed). Currently, device mapper fails the path for this error and eventually this will lead to I/O error. We don't want to see I/O error for this reason.
The patch will set the flag pg_init_required if the device is running on single path. The process_queued_ios will re-initialize path if required. I have tested this patch on LSI rdac handler.
Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
--- linux-2.6.30-rc2/drivers/md/dm-mpath.c.orig 2009-04-17 16:49:33.000000000 -0500
+++ linux-2.6.30-rc2/drivers/md/dm-mpath.c 2009-04-17 17:09:51.000000000 -0500
@@ -1152,6 +1152,15 @@ static int do_end_io(struct multipath *m
return error;
spin_lock_irqsave(&m->lock, flags);
+ /*
+ * If this is the only path left, then lets try to
+ * re-initialize the PG one last time..
+ */
+ if (m->nr_valid_paths == 1 && m->hw_handler_name) {
+ m->pg_init_required = 1;
+ spin_unlock_irqrestore(&m->lock, flags);
+ goto requeue;
+ }
if (!m->nr_valid_paths) {
if (__must_push_back(m)) {
spin_unlock_irqrestore(&m->lock, flags);
--
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