[PATCH] scsi: sd: Contribute to randomness when running rotational device

[Xuewei Zhang]

Currently a scsi device won't contribute to kernel randomness when it
uses blk-mq. Since we commonly use scsi on rotational device with
blk-mq, it make sense to keep contributing to kernel randomness in these
cases. This is especially important for virtual machines.

commit b5b6e8c8d3b4 ("scsi: virtio_scsi: fix IO hang caused by automatic
irq vector affinity") made all virtio-scsi device to use blk-mq, which
does not contribute to randomness today. So for a virtual machine only
having virtio-scsi disk (which is common), it will simple stop getting
randomness from its disks in today's implementation.

With this patch, if the above VM has rotational virtio-scsi device, then
it can still benefit from the entropy generated from the disk.

Reported-by: Xuewei Zhang <xueweiz@xxxxxxxxxx>
Signed-off-by: Xuewei Zhang <xueweiz@xxxxxxxxxx>
---
 drivers/scsi/sd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index b79b366a94f7..5e4f10d28065 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2959,6 +2959,9 @@ 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) {
-- 
2.19.0.rc2.392.g5ba43deb5a-goog