linux-kernel - Re: [PATCH 2/5] rhashtable: don't hold lock on first table throughout insertion.

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Message-ID: <87h8kqrhi0.fsf@notabene.neil.brown.name>
Date:   Mon, 23 Jul 2018 09:13:43 +1000
From:   NeilBrown <neilb@...e.com>
To:     paulmck@...ux.vnet.ibm.com
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] rhashtable: don't hold lock on first table throughout insertion.

On Sun, Jul 22 2018, Paul E. McKenney wrote:
>
> One issue is that the ->func pointer can legitimately be NULL while on
> RCU's callback lists.  This happens when someone invokes kfree_rcu()
> with the rcu_head structure at the beginning of the enclosing structure.
> I could add an offset to avoid this, or perhaps the kmalloc() folks
> could be persuaded Rao Shoaib's patch moving kfree_rcu() handling to
> the slab allocators, so that RCU only ever sees function pointers in
> the ->func field.
>
> Either way, this should be hidden behind an API to allow adjustments
> to be made if needed.  Maybe something like is_after_call_rcu()?
> This would (for example) allow debug-object checks to be used to catch
> check-after-free bugs.
>
> Would something of that sort work for you?

Yes, if you could provide an is_after_call_rcu() API, that would
perfectly suit my use-case.
Thanks,
NeilBrown

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