md: revert incorrect fix for read error handling in raid1.

commit 4706b349f was a forward port of a fix that was needed
for SLES10. But in fact it is not needed in mainline because
the earlier commit dd00a99e7a fixes the same problem in a
better way.
Further, this commit introduces a bug in the way it interacts with
the automatic read-error-correction. If, after a read error is
successfully corrected, the same disk is chosen to re-read - the
re-read won't be attempted but an error will be returned instead.

After reverting that commit, there is the possibility that a
read error on a read-only array (where read errors cannot
be corrected as that requires a write) will repeatedly read the same
device and continue to get an error.
So in the "Array is readonly" case, fail the drive immediately on
a read error.

Signed-off-by: NeilBrown <[e-mail]>
Cc: [e-mail]

drivers/md/raid1.c

···
 					       r1_bio->sector,
 					       r1_bio->sectors);
 				unfreeze_array(conf);
-			}
+			} else
+				md_error(mddev,
+					 conf->mirrors[r1_bio->read_disk].rdev);
 
 			bio = r1_bio->bios[r1_bio->read_disk];
-			if ((disk=read_balance(conf, r1_bio)) == -1 ||
-			    disk == r1_bio->read_disk) {
+			if ((disk=read_balance(conf, r1_bio)) == -1) {
 				printk(KERN_ALERT "raid1: %s: unrecoverable I/O"
 				       " read error for block %llu\n",
 				       bdevname(bio->bi_bdev,b),