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

[NeilBrown <neilb@suse.com>]

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On Mon, Jun 04 2018, Simon Horman wrote:

> 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/
>

Thanks :-)  I've made that change for when I formally submit.

Thanks,
NeilBrown

>> 
>> 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>

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