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From: David Miller <davem@davemloft.net>
To: neilb@suse.com
Cc: herbert@gondor.apana.org.au, tgraf@suug.ch,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	eric.dumazet@gmail.com
Subject: Re: [PATCH v3] rhashtable: detect when object movement between tables might have invalidated a lookup
Date: Mon, 03 Dec 2018 15:32:09 -0800 (PST)	[thread overview]
Message-ID: <20181203.153209.2147928207639502351.davem@davemloft.net> (raw)
In-Reply-To: <87pnuno479.fsf@notabene.neil.brown.name>

From: NeilBrown <neilb@suse.com>
Date: Fri, 30 Nov 2018 10:26:50 +1100

> 
> Some users of rhashtables might need to move an object from one table
> to another -  this appears to be the reason for the incomplete usage
> of NULLS markers.
> 
> To support these, we store a unique NULLS_MARKER at the end of
> each chain, and when a search fails to find a match, we check
> if the NULLS marker found was the expected one.  If not, the search
> may not have examined all objects in the target bucket, so it is
> repeated.
> 
> The unique NULLS_MARKER is derived from the address of the
> head of the chain.  As this cannot be derived at load-time the
> static rhnull in rht_bucket_nested() needs to be initialised
> at run time.
> 
> Any caller of a lookup function must still be prepared for the
> possibility that the object returned is in a different table - it
> might have been there for some time.
> 
> Note that this does NOT provide support for other uses of
> NULLS_MARKERs such as allocating with SLAB_TYPESAFE_BY_RCU or changing
> the key of an object and re-inserting it in the same table.
> These could only be done safely if new objects were inserted
> at the *start* of a hash chain, and that is not currently the case.
> 
> Signed-off-by: NeilBrown <neilb@suse.com>

Applied to net-next.

      parent reply	other threads:[~2018-12-03 23:32 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-14 23:32 [PATCH] rhashtable: detect when object movement between tables might have invalidated a lookup NeilBrown
2018-11-16  5:55 ` Herbert Xu
2018-11-16  6:59   ` NeilBrown
2018-11-19  3:54     ` Herbert Xu
2018-11-19  3:56       ` Herbert Xu
2018-11-19  4:06         ` Herbert Xu
2018-11-19  4:22           ` David Miller
2018-11-29 23:26     ` [PATCH v3] " NeilBrown
2018-12-01  8:47       ` Herbert Xu
2018-12-02 22:20         ` NeilBrown
2018-12-03  1:44           ` Herbert Xu
2018-12-03 22:28             ` [PATCH] " NeilBrown
2018-12-03 23:32       ` David Miller [this message]

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