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[SCSI] zfcp: fix cleanup of dismissed error recovery actions 

Calling zfcp_erp_strategy_check_action() after zfcp_erp_action_to_running()
in zfcp_erp_strategy() might cause an unbalanced up() for erp_ready_sem,
which makes the zfcp recovery fail somewhere along the way:

erp thread processing erp_action:
|
|	someone waking up erp thread for erp_action
|	|
|	|		someone else dismissing erp_action:
|	|		|
V	V		V

	write_lock_irqsave(&adapter->erp_lock, flags);
	...
	if (zfcp_erp_action_exists(erp_action) == ZFCP_ERP_ACTION_RUNNING) {
		zfcp_erp_action_to_ready(erp_action);
		up(&adapter->erp_ready_sem);	/* first up() for erp_action */
	}
	write_unlock_irqrestore(&adapter->erp_lock, flags);

write_lock_irqsave(&adapter->erp_lock, flags);
...
zfcp_erp_action_to_running(erp_action);
write_unlock_restore(&adapter->erp_lock, flags);
/* processing erp_action */

			write_lock_irqsave(&adapter->erp_lock, flags);
			...
			erp_action->status |= ZFCP_STATUS_ERP_DISMISSED;
			if (zfcp_erp_action_exists(erp_action) ==
						ZFCP_ERP_ACTION_RUNNING) {
				zfcp_erp_action_to_ready(erp_action);
				up(&adapter->erp_ready_sem);
				/* second, unbalanced up() for erp_action */
			}
			...
			write_unlock_restore(&adapter->erp_lock, flags);

write_lock_irqsave(&adapter->erp_lock, flags);
if (erp_action->status & ZFCP_STATUS_ERP_DISMISSED) {
	zfcp_erp_action_dequeue(erp_action);
	retval = ZFCP_ERP_DISMISSED;
}
...
write_unlock_restore(&adapter->erp_lock, flags);
down(&adapter->erp_ready_sem);
/* this down() is meant to balance the first up() */

The erp thread must not dismiss an erp_action after moving that action to
erp_running_head. Instead it should just go through the down() operation,
which balances the first up(), and run through zfcp_erp_strategy one more
time for the second up(), which eventually cleans up erp_action. Which
is similar to the normal processing of an event for erp_action doing
something asynchronously (e.g. waiting for the completion of an fsf_req).

This only works if we make sure that a dismissed erp_action is passed to
zfcp_erp_strategy() prior to the other action, which caused actions to be
dismissed. Therefore the patch implements this rule: running actions go to
the head of the ready list; new actions go to the tail of the ready list;
the erp thread picks actions to be processed from the ready list's head.

Signed-off-by: Martin Peschke <mp3@de.ibm.com>
Acked-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
This commit is contained in:
Martin Peschke 2007-11-15 13:57:17 +01:00 committed by James Bottomley
parent d0076f7754
commit 86e8dfc560
1 changed files with 6 additions and 8 deletions
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14
drivers/s390/scsi/zfcp_erp.c
View File

@ -1065,7 +1065,7 @@ zfcp_erp_thread(void *data)
&adapter->status)) {
write_lock_irqsave(&adapter->erp_lock, flags);
next = adapter->erp_ready_head.prev;
next = adapter->erp_ready_head.next;
write_unlock_irqrestore(&adapter->erp_lock, flags);
if (next != &adapter->erp_ready_head) {
@ -1155,15 +1155,13 @@ zfcp_erp_strategy(struct zfcp_erp_action *erp_action)
/*
* check for dismissed status again to avoid follow-up actions,
* failing of targets and so on for dismissed actions
* failing of targets and so on for dismissed actions,
* we go through down() here because there has been an up()
*/
retval = zfcp_erp_strategy_check_action(erp_action, retval);
if (erp_action->status & ZFCP_STATUS_ERP_DISMISSED)
retval = ZFCP_ERP_CONTINUES;
switch (retval) {
case ZFCP_ERP_DISMISSED:
/* leave since this action has ridden to its ancestors */
debug_text_event(adapter->erp_dbf, 6, "a_st_dis2");
goto unlock;
case ZFCP_ERP_NOMEM:
/* no memory to continue immediately, let it sleep */
if (!(erp_action->status & ZFCP_STATUS_ERP_LOWMEM)) {
@ -3091,7 +3089,7 @@ zfcp_erp_action_enqueue(int action,
++adapter->erp_total_count;
/* finally put it into 'ready' queue and kick erp thread */
list_add(&erp_action->list, &adapter->erp_ready_head);
list_add_tail(&erp_action->list, &adapter->erp_ready_head);
up(&adapter->erp_ready_sem);
retval = 0;
out: