Re: [PATCH 15a/18] rhashtables: add lockdep tracking to bucket bit-spin-locks.

Simon Horman
2018-06-04T18:16:10Z

On Mon, Jun 04, 2018 at 12:52:54PM +1000, NeilBrown wrote:
>
> Native bit_spin_locks are not tracked by lockdep.
>
> The bit_spin_locks used for rhashtable buckets are local
> to the rhashtable implementation, so there is little opportunity
> for the sort of misuse that lockdep might detect.
> However locks are held while a hash function or compare
> function is called, and if one of these took a lock,
> a misbehaviour is possible.
>
> As it is quite easy to add lockdep support this unlikely
> possibility see to be enough justification.

nit: s/see/seems/

>
> So create a lockdep class for bucket bit_spin_lock as attach
> through a lockdep_map in each bucket_table.
>
> With the 'nested' annotation in rhashtable_rehash_one(), lockdep
> correctly reports a possible problem as this lock it taken
> while another bucket lock (in another table) is held. This
> confirms that the added support works.
> With the correct nested annotation in place, lockdep reports
> no problems.
>
> Signed-off-by: NeilBrown <neilb@suse.com>