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

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Message-ID: <20180604181609.sssd4ao6wfwj3il6@netronome.com>
Date:   Mon, 4 Jun 2018 20:16:10 +0200
From:   Simon Horman <simon.horman@...ronome.com>
To:     NeilBrown <neilb@...e.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 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@...e.com>