Messages in this thread | | | Date | Wed, 11 Jul 2018 22:48:01 -0700 (PDT) | Subject | Re: [PATCH resend] rhashtable: detect when object movement might have invalidated a lookup | From | David Miller <> |
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From: David Miller <davem@davemloft.net> Date: Wed, 11 Jul 2018 22:46:58 -0700 (PDT)
> From: NeilBrown <neilb@suse.com> > Date: Fri, 06 Jul 2018 17:08:35 +1000 > >> >> Some users of rhashtable might need to change the key >> of an object and move it to a different location in the table. >> Other users might want to allocate objects using >> SLAB_TYPESAFE_BY_RCU which can result in the same memory allocation >> being used for a different (type-compatible) purpose and similarly >> end up in a different hash-chain. >> >> 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 is repeated. >> >> The unique NULLS_MARKER is derived from the address of the >> head of the chain. >> >> If an object is removed and re-added to the same hash chain, we won't >> notice by looking that the NULLS marker. In this case we must be sure >> that it was not re-added *after* its original location, or a lookup may >> incorrectly fail. The easiest solution is to ensure it is inserted at >> the start of the chain. insert_slow() already does that, >> insert_fast() does not. So this patch changes insert_fast to always >> insert at the head of the chain. >> >> Note that such a user must do their own double-checking of >> the object found by rhashtable_lookup_fast() after ensuring >> mutual exclusion which anything that might change the key, such as >> successfully taking a new reference. >> >> Signed-off-by: NeilBrown <neilb@suse.com> > > Applied to net-next.
Actually, reverted, it doesn't even compile.
lib/rhashtable.c: In function ‘rht_bucket_nested’: lib/rhashtable.c:1187:39: error: macro "INIT_RHT_NULLS_HEAD" passed 3 arguments, but takes just 1 INIT_RHT_NULLS_HEAD(rhnull, NULL, 0); ^ lib/rhashtable.c:1187:4: error: ‘INIT_RHT_NULLS_HEAD’ undeclared (first use in this function); did you mean ‘INIT_LIST_HEAD’? INIT_RHT_NULLS_HEAD(rhnull, NULL, 0); ^~~~~~~~~~~~~~~~~~~ INIT_LIST_HEAD lib/rhashtable.c:1187:4: note: each undeclared identifier is reported only once for each function it appears in
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