scsi: sd: fix entropy gathering for most rotational disks

The problem is that the default for MQ is not to gather entropy, whereas
the default for the legacy queue was always to gather it.  The original
attempt to fix entropy gathering for rotational disks under MQ added an
else branch in sd_read_block_characteristics().  Unfortunately, the entire
check isn't reached if the device has no characteristics VPD page.  Since
this page was only introduced in SBC-3 and its optional anyway, most less
expensive rotational disks don't have one, meaning they all stopped
gathering entropy when we made MQ the default.  In a wholly unrelated
change, openssl and openssh won't function until the random number
generator is initialised, meaning lots of people have been seeing large
delays before they could log into systems with default MQ kernels due to
this lack of entropy, because it now can take tens of minutes to initialise
the kernel random number generator.

The fix is to set the non-rotational and add-randomness flags
unconditionally early on in the disk initialization path, so they can be
reset only if the device actually reports being non-rotational via the VPD
page.

Reported-by: Mikael Pettersson <mikpelinux@gmail.com>
Fixes: 83e32a5 ("scsi: sd: Contribute to randomness when running rotational device")
Cc: stable@vger.kernel.org
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Xuewei Zhang <xueweiz@google.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sd.c

@@ -2951,9 +2951,6 @@ static void sd_read_block_characteristics(struct scsi_disk *sdkp)
 	if (rot == 1) {
 		blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
 		blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, q);
-	} else {
-		blk_queue_flag_clear(QUEUE_FLAG_NONROT, q);
-		blk_queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q);
 	}
 
 	if (sdkp->device->type == TYPE_ZBC) {
@@ -3090,6 +3087,15 @@ static int sd_revalidate_disk(struct gendisk *disk)
 	if (sdkp->media_present) {
 		sd_read_capacity(sdkp, buffer);
 
+		/*
+		 * set the default to rotational.  All non-rotational devices
+		 * support the block characteristics VPD page, which will
+		 * cause this to be updated correctly and any device which
+		 * doesn't support it should be treated as rotational.
+		 */
+		blk_queue_flag_clear(QUEUE_FLAG_NONROT, q);
+		blk_queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q);
+
 		if (scsi_device_supports_vpd(sdp)) {
 			sd_read_block_provisioning(sdkp);
 			sd_read_block_limits(sdkp);