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>

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index f90069029aaeed02ab6f4f61814afc92d13db2f0..77b90ae66991509dce928756d567b14dd4fb192e 100644 (file)
--- 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;
        }
 
@@ -1396,13 +1404,23 @@ 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);
 
        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