tree 82d2783ae0067d762f88f9cbb51b5a15eb7d339b
parent 64f63d59ba782ec317fca150895ef8dc6ddbff4b
author Paolo Abeni <pabeni@redhat.com> 1455288233 +0100
committer David S. Miller <davem@davemloft.net> 1455672108 -0500

net: add dst_cache support

This patch add a generic, lockless dst cache implementation.
The need for lock is avoided updating the dst cache fields
only in per cpu scope, and requiring that the cache manipulation
functions are invoked with the local bh disabled.

The refresh_ts and reset_ts fields are used to ensure the cache
consistency in case of cuncurrent cache update (dst_cache_set*) and
reset operation (dst_cache_reset).

Consider the following scenario:

CPU1:                                   	CPU2:
  <cache lookup with emtpy cache: it fails>
  <get dst via uncached route lookup>
						<related configuration changes>
                                        	dst_cache_reset()
  dst_cache_set()

The dst entry set passed to dst_cache_set() should not be used
for later dst cache lookup, because it's obtained using old
configuration values.

Since the refresh_ts is updated only on dst_cache lookup, the
cached value in the above scenario will be discarded on the next
lookup.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Suggested-and-acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>