raid5 improve too many read errors msg by adding limits

Often limits can be changed by admin. When discussing such things
it helps if you can provide "self-sustained" facts. Also
sometimes the admin thinks he changed a limit, but it did not
take effect for some reason or he changed the wrong thing.

V3: Only pr_warn when Faulty is 0.
V2: Add read_errors value to pr_warn.
Signed-off-by: Nigel Croxon <ncroxon@redhat.com>
Signed-off-by: Song Liu <songliubraving@fb.com>

drivers/md/raid5.c

@@ -2549,10 +2549,16 @@ static void raid5_end_read_request(struct bio * bi)
 				(unsigned long long)s,
 				bdn);
 		} else if (atomic_read(&rdev->read_errors)
-			 > conf->max_nr_stripes)
-			pr_warn("md/raid:%s: Too many read errors, failing device %s.\n",
-			       mdname(conf->mddev), bdn);
-		else
+			 > conf->max_nr_stripes) {
+			if (!test_bit(Faulty, &rdev->flags)) {
+				pr_warn("md/raid:%s: %d read_errors > %d stripes\n",
+				    mdname(conf->mddev),
+				    atomic_read(&rdev->read_errors),
+				    conf->max_nr_stripes);
+				pr_warn("md/raid:%s: Too many read errors, failing device %s.\n",
+				    mdname(conf->mddev), bdn);
+			}
+		} else
 			retry = 1;
 		if (set_bad && test_bit(In_sync, &rdev->flags)
 		    && !test_bit(R5_ReadNoMerge, &sh->dev[i].flags))