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

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Message-ID: <87bmcqp717.fsf@notabene.neil.brown.name>
Date:   Tue, 05 Jun 2018 07:37:40 +1000
From:   NeilBrown <neilb@...e.com>
To:     Simon Horman <simon.horman@...ronome.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 15a/18] rhashtables: add lockdep tracking to bucket bit-spin-locks.

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@...e.com>

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