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md: make ->congested robust against personality changes.

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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>
This commit is contained in:
NeilBrown 2014-12-15 12:56:56 +11:00
parent 85572d7c75
commit 5c675f83c6
12 changed files with 38 additions and 77 deletions
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8
drivers/md/dm-raid.c
View file

@ -746,13 +746,7 @@ static int raid_is_congested(struct dm_target_callbacks *cb, int bits)
{
struct raid_set *rs = container_of(cb, struct raid_set, callbacks);
if (rs->raid_type->level == 1)
return md_raid1_congested(&rs->md, bits);
if (rs->raid_type->level == 10)
return md_raid10_congested(&rs->md, bits);
return md_raid5_congested(&rs->md, bits);
return mddev_congested(&rs->md, bits);
}
/*