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    Subject[RFCv7 PATCH 3/4] net/sock.h: use poll_does_not_wait() in sock_poll_wait()
    Date
    From: Hans Verkuil <hans.verkuil@cisco.com>

    In order to determine whether poll_wait() might actually wait the
    poll_table pointer was tested in sock_poll_wait(). This is no longer
    sufficient, instead poll_does_not_wait() should be called. That function
    also tests whether pt->pq_proc is non-NULL.

    Without this change smp_mb() could be called unnecessarily in some
    circumstances, causing a performance hit.

    Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
    ---
    include/net/sock.h | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
    diff --git a/include/net/sock.h b/include/net/sock.h
    index 91c1c8b..da7f2ec 100644
    --- a/include/net/sock.h
    +++ b/include/net/sock.h
    @@ -1824,7 +1824,7 @@ static inline bool wq_has_sleeper(struct socket_wq *wq)
    static inline void sock_poll_wait(struct file *filp,
    wait_queue_head_t *wait_address, poll_table *p)
    {
    - if (p && wait_address) {
    + if (!poll_does_not_wait(p) && wait_address) {
    poll_wait(filp, wait_address, p);
    /*
    * We need to be sure we are in sync with the
    --
    1.7.8.3


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