• Willem de Bruijn's avatar
    ipv6: elide flowlabel check if no exclusive leases exist · 59c820b2
    Willem de Bruijn authored
    Processes can request ipv6 flowlabels with cmsg IPV6_FLOWINFO.
    If not set, by default an autogenerated flowlabel is selected.
    Explicit flowlabels require a control operation per label plus a
    datapath check on every connection (every datagram if unconnected).
    This is particularly expensive on unconnected sockets multiplexing
    many flows, such as QUIC.
    In the common case, where no lease is exclusive, the check can be
    safely elided, as both lease request and check trivially succeed.
    Indeed, autoflowlabel does the same even with exclusive leases.
    Elide the check if no process has requested an exclusive lease.
    fl6_sock_lookup previously returns either a reference to a lease or
    NULL to denote failure. Modify to return a real error and update
    all callers. On return NULL, they can use the label and will elide
    the atomic_dec in fl6_sock_release.
    This is an optimization. Robust applications still have to revert to
    requesting leases if the fast path fails due to an exclusive lease.
    Changes RFC->v1:
      - use static_key_false_deferred to rate limit jump label operations
        - call static_key_deferred_flush to stop timers on exit
      - move decrement out of RCU context
      - defer optimization also if opt data is associated with a lease
      - updated all fp6_sock_lookup callers, not just udp
    Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
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