md/raid5: deadlock between retry_aligned_read with barrier io

A chunk aligned read increases counter active_aligned_reads and
decreases it after sub-device handle it successfully. But when a read
error occurs,  the read redispatched by raid5d, and the
active_aligned_reads will not be decreased until we can grab a stripe
head in retry_aligned_read. Now suppose, a barrier io comes, set
conf->quiesce to 2, and wait until both active_stripes and
active_aligned_reads are zero. The retried chunk aligned read gets
stuck at get_active_stripe waiting until conf->quiesce becomes 0.
Retry_aligned_read and barrier io are waiting each other now.
One possible solution is that we ignore conf->quiesce, let the retried
aligned read finish. I reproduced this deadlock and test this patch on
centos6.0

Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid5.c

@@ -5115,7 +5115,7 @@ static int  retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
 			/* already done this stripe */
 			continue;
 
-		sh = get_active_stripe(conf, sector, 0, 1, 0);
+		sh = get_active_stripe(conf, sector, 0, 1, 1);
 
 		if (!sh) {
 			/* failed to get a stripe - must wait */