Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections

[Herbert Xu <herbert@gondor.apana.org.au>]

David S. Miller <davem@davemloft.net> wrote:
> 
> I agree with the changes to add rcu_dereference() use.
> Those were definitely lacking and needed.

Actually I'm not so sure that they are all needed.  I only looked
at the very first one in the patch which is in in_dev_get().  That
one certainly isn't necessary because the old value of ip_ptr
is valid as long as the reference count does not hit zero.

The later is guaranteed by the increment in in_dev_get().

Because the pervasiveness of reference counting in the network stack,
I believe that we should scrutinise the other bits in the patch too
to make sure that they are all needed.

In general, using rcu_dereference/rcu_assign_pointer does not
guarantee correct code.  We really need to look at each case
individually.

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
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