md: make ->congested robust against personality changes.

There is currently no locking around calls to the 'congested'
bdi function.  If called at an awkward time while an array is
being converted from one level (or personality) to another, there
is a tiny chance of running code in an unreferenced module etc.

So add a 'congested' function to the md_personality operations
structure, and call it with appropriate locking from a central
'mddev_congested'.

When the array personality is changing the array will be 'suspended'
so no IO is processed.
If mddev_congested detects this, it simply reports that the
array is congested, which is a safe guess.
As mddev_suspend calls synchronize_rcu(), mddev_congested can
avoid races by included the whole call inside an rcu_read_lock()
region.
This require that the congested functions for all subordinate devices
can be run under rcu_lock.  Fortunately this is the case.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 2 insertions, 7 deletions

diff --git a/drivers/md/linear.c b/drivers/md/linear.c
index 64713b77df1c..05108510d9cd 100644
--- a/drivers/md/linear.c
+++ b/drivers/md/linear.c
@@ -97,15 +97,11 @@ static int linear_mergeable_bvec(struct request_queue *q,
                 return maxsectors << 9;
 }
 
-static int linear_congested(void *data, int bits)
+static int linear_congested(struct mddev *mddev, int bits)
 {
-        struct mddev *mddev = data;
         struct linear_conf *conf;
         int i, ret = 0;
 
-        if (mddev_congested(mddev, bits))
-                return 1;
-
         rcu_read_lock();
         conf = rcu_dereference(mddev->private);
 
@@ -218,8 +214,6 @@ static int linear_run (struct mddev *mddev)
         md_set_array_sectors(mddev, linear_size(mddev, 0, 0));
 
         blk_queue_merge_bvec(mddev->queue, linear_mergeable_bvec);
-        mddev->queue->backing_dev_info.congested_fn = linear_congested;
-        mddev->queue->backing_dev_info.congested_data = mddev;
 
         ret =  md_integrity_register(mddev);
         if (ret) {
@@ -366,6 +360,7 @@ static struct md_personality linear_personality =
         .status         = linear_status,
         .hot_add_disk   = linear_add,
         .size           = linear_size,
+        .congested      = linear_congested,
 };
 
 static int __init linear_init (void)