dm table: clear add_random unless all devices have it set

Always clear QUEUE_FLAG_ADD_RANDOM if any underlying device does not
have it set. Otherwise devices with predictable characteristics may
contribute entropy.

QUEUE_FLAG_ADD_RANDOM specifies whether or not queue IO timings
contribute to the random pool.

For bio-based targets this flag is always 0 because such devices have no
real queue.

For request-based devices this flag was always set to 1 by default.

Now set it according to the flags on underlying devices. If there is at
least one device which should not contribute, set the flag to zero: If a
device, such as fast SSD storage, is not suitable for supplying entropy,
a request-based queue stacked over it will not be either.

Because the checking logic is exactly same as for the rotational flag,
share the iteration function with device_is_nonrot().

Signed-off-by: Milan Broz <mbroz@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 22 insertions, 4 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index f90069029aae..77b90ae66991 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1354,17 +1354,25 @@ static int device_is_nonrot(struct dm_target *ti, struct dm_dev *dev,
         return q && blk_queue_nonrot(q);
 }
 
-static bool dm_table_is_nonrot(struct dm_table *t)
+static int device_is_not_random(struct dm_target *ti, struct dm_dev *dev,
+                             sector_t start, sector_t len, void *data)
+{
+        struct request_queue *q = bdev_get_queue(dev->bdev);
+
+        return q && !blk_queue_add_random(q);
+}
+
+static bool dm_table_all_devices_attribute(struct dm_table *t,
+                                           iterate_devices_callout_fn func)
 {
         struct dm_target *ti;
         unsigned i = 0;
 
-        /* Ensure that all underlying device are non-rotational. */
         while (i < dm_table_get_num_targets(t)) {
                 ti = dm_table_get_target(t, i++);
 
                 if (!ti->type->iterate_devices ||
-                    !ti->type->iterate_devices(ti, device_is_nonrot, NULL))
+                    !ti->type->iterate_devices(ti, func, NULL))
                         return 0;
         }
 
@@ -1396,7 +1404,8 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
         if (!dm_table_discard_zeroes_data(t))
                 q->limits.discard_zeroes_data = 0;
 
-        if (dm_table_is_nonrot(t))
+        /* Ensure that all underlying devices are non-rotational. */
+        if (dm_table_all_devices_attribute(t, device_is_nonrot))
                 queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
         else
                 queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
@@ -1404,6 +1413,15 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
         dm_table_set_integrity(t);
 
         /*
+         * Determine whether or not this queue's I/O timings contribute
+         * to the entropy pool, Only request-based targets use this.
+         * Clear QUEUE_FLAG_ADD_RANDOM if any underlying device does not
+         * have it set.
+         */
+        if (blk_queue_add_random(q) && dm_table_all_devices_attribute(t, device_is_not_random))
+                queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, q);
+
+        /*
          * QUEUE_FLAG_STACKABLE must be set after all queue settings are
          * visible to other CPUs because, once the flag is set, incoming bios
          * are processed by request-based dm, which refers to the queue