ocfs2: use spinlock irqsave for downconvert lock.patch

When ocfs2dc thread holds dc_task_lock spinlock and receives soft IRQ it
deadlock itself trying to get same spinlock in ocfs2_wake_downconvert_thread.
Below is the stack snippet.

The patch disables interrupts when acquiring dc_task_lock spinlock.

	ocfs2_wake_downconvert_thread
	ocfs2_rw_unlock
	ocfs2_dio_end_io
	dio_complete
	.....
	bio_endio
	req_bio_endio
	....
	scsi_io_completion
	blk_done_softirq
	__do_softirq
	do_softirq
	irq_exit
	do_IRQ
	ocfs2_downconvert_thread
	[kthread]
Signed-off-by: Srinivas Eeda <srinivas.eeda@oracle.com>
Signed-off-by: Joel Becker <jlbec@evilplan.org>

fs/ocfs2/dlmglue.c

@@ -3932,6 +3932,8 @@ static void ocfs2_process_blocked_lock(struct ocfs2_super *osb,
 static void ocfs2_schedule_blocked_lock(struct ocfs2_super *osb,
 					struct ocfs2_lock_res *lockres)
 {
+	unsigned long flags;
+
 	assert_spin_locked(&lockres->l_lock);
 
 	if (lockres->l_flags & OCFS2_LOCK_FREEING) {
@@ -3945,21 +3947,22 @@ static void ocfs2_schedule_blocked_lock(struct ocfs2_super *osb,
 
 	lockres_or_flags(lockres, OCFS2_LOCK_QUEUED);
 
-	spin_lock(&osb->dc_task_lock);
+	spin_lock_irqsave(&osb->dc_task_lock, flags);
 	if (list_empty(&lockres->l_blocked_list)) {
 		list_add_tail(&lockres->l_blocked_list,
 			      &osb->blocked_lock_list);
 		osb->blocked_lock_count++;
 	}
-	spin_unlock(&osb->dc_task_lock);
+	spin_unlock_irqrestore(&osb->dc_task_lock, flags);
 }
 
 static void ocfs2_downconvert_thread_do_work(struct ocfs2_super *osb)
 {
 	unsigned long processed;
+	unsigned long flags;
 	struct ocfs2_lock_res *lockres;
 
-	spin_lock(&osb->dc_task_lock);
+	spin_lock_irqsave(&osb->dc_task_lock, flags);
 	/* grab this early so we know to try again if a state change and
 	 * wake happens part-way through our work  */
 	osb->dc_work_sequence = osb->dc_wake_sequence;
@@ -3972,38 +3975,40 @@ static void ocfs2_downconvert_thread_do_work(struct ocfs2_super *osb)
 				     struct ocfs2_lock_res, l_blocked_list);
 		list_del_init(&lockres->l_blocked_list);
 		osb->blocked_lock_count--;
-		spin_unlock(&osb->dc_task_lock);
+		spin_unlock_irqrestore(&osb->dc_task_lock, flags);
 
 		BUG_ON(!processed);
 		processed--;
 
 		ocfs2_process_blocked_lock(osb, lockres);
 
-		spin_lock(&osb->dc_task_lock);
+		spin_lock_irqsave(&osb->dc_task_lock, flags);
 	}
-	spin_unlock(&osb->dc_task_lock);
+	spin_unlock_irqrestore(&osb->dc_task_lock, flags);
 }
 
 static int ocfs2_downconvert_thread_lists_empty(struct ocfs2_super *osb)
 {
 	int empty = 0;
+	unsigned long flags;
 
-	spin_lock(&osb->dc_task_lock);
+	spin_lock_irqsave(&osb->dc_task_lock, flags);
 	if (list_empty(&osb->blocked_lock_list))
 		empty = 1;
 
-	spin_unlock(&osb->dc_task_lock);
+	spin_unlock_irqrestore(&osb->dc_task_lock, flags);
 	return empty;
 }
 
 static int ocfs2_downconvert_thread_should_wake(struct ocfs2_super *osb)
 {
 	int should_wake = 0;
+	unsigned long flags;
 
-	spin_lock(&osb->dc_task_lock);
+	spin_lock_irqsave(&osb->dc_task_lock, flags);
 	if (osb->dc_work_sequence != osb->dc_wake_sequence)
 		should_wake = 1;
-	spin_unlock(&osb->dc_task_lock);
+	spin_unlock_irqrestore(&osb->dc_task_lock, flags);
 
 	return should_wake;
 }
@@ -4033,10 +4038,12 @@ static int ocfs2_downconvert_thread(void *arg)
 
 void ocfs2_wake_downconvert_thread(struct ocfs2_super *osb)
 {
-	spin_lock(&osb->dc_task_lock);
+	unsigned long flags;
+
+	spin_lock_irqsave(&osb->dc_task_lock, flags);
 	/* make sure the voting thread gets a swipe at whatever changes
 	 * the caller may have made to the voting state */
 	osb->dc_wake_sequence++;
-	spin_unlock(&osb->dc_task_lock);
+	spin_unlock_irqrestore(&osb->dc_task_lock, flags);
 	wake_up(&osb->dc_event);
 }