scsi: sd: Contribute to randomness when running rotational device

Xuewei Zhang · martinkpetersen · commit 83e32a591077 · 2018-09-17T02:57:10.000-04:00
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 b5b6e8c ("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@google.com> Signed-off-by: Xuewei Zhang <xueweiz@google.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Maciej Żenczykowski <maze@google.com> Reviewed-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
diff --git 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) {

Original file line number	Diff line number	Diff line change
`@@ -2959,6 +2959,9 @@ static void sd_read_block_characteristics(struct scsi_disk *sdkp)`
`2959`	`2959`	`if (rot == 1) {`
`2960`	`2960`	`blk_queue_flag_set(QUEUE_FLAG_NONROT, q);`
`2961`	`2961`	`blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, q);`
	`2962`	`+ } else {`
	`2963`	`+ blk_queue_flag_clear(QUEUE_FLAG_NONROT, q);`
	`2964`	`+ blk_queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q);`
`2962`	`2965`	`}`
`2963`	`2966`
`2964`	`2967`	`if (sdkp->device->type == TYPE_ZBC) {`