From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller 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) Message-ID: <20181203.153209.2147928207639502351.davem@davemloft.net> References: <20181116055551.zxfydbpoicslsfkg@gondor.apana.org.au> <878t1tece0.fsf@notabene.neil.brown.name> <87pnuno479.fsf@notabene.neil.brown.name> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: herbert@gondor.apana.org.au, tgraf@suug.ch, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, eric.dumazet@gmail.com To: neilb@suse.com Return-path: In-Reply-To: <87pnuno479.fsf@notabene.neil.brown.name> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: NeilBrown 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 Applied to net-next.