On Mon, Oct 25, 2010 at 01:10:24PM +1100, Neil Brown wrote:
> On Sun, 24 Oct 2010 21:21:33 -0400
> "J. Bruce Fields" <bfields@xxxxxxxxxx> wrote:
>
> > The only caller (svc_send) has already checked XPT_DEAD.
> >
> > Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> > ---
> > net/sunrpc/svcsock.c | 3 ---
> > 1 files changed, 0 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> > index 1454739..07919e1 100644
> > --- a/net/sunrpc/svcsock.c
> > +++ b/net/sunrpc/svcsock.c
> > @@ -1135,9 +1135,6 @@ static int svc_tcp_sendto(struct svc_rqst *rqstp)
> > reclen = htonl(0x80000000|((xbufp->len ) - 4));
> > memcpy(xbufp->head[0].iov_base, &reclen, 4);
> >
> > - if (test_bit(XPT_DEAD, &rqstp->rq_xprt->xpt_flags))
> > - return -ENOTCONN;
> > -
> > sent = svc_sendto(rqstp, &rqstp->rq_res);
> > if (sent != xbufp->len) {
> > printk(KERN_NOTICE
>
>
> So after removing all these references to XPT_DEAD, do we need XPT_DEAD at
> all???
>
> I think it is only used in two other places.
>
> 1/ In svc_revisit we don't queue the deferred request to an XPT_DEAD
> transport.
> We could avoid that but changing the 'owner' of a deferred request from the
> service to the xprt, and call cache_clean_deferred in svc_delete_xprt
That use does seem a bit of a hack to me, so I'd be happy to get rid of
it.
> 2/ in svc_send(). I wonder if we need this at all. There doesn't seem to be
> any locking to ensure that XPT_DEAD doesn't get set immediately after the
> test, and the underlying sendto (whether tcp or udp or whatever) should fail
> if the socket is closed, and if it doesn't it shouldn't really matter??
Does it make a difference in the case of a half-close? If the client
follows a request immediately by a FIN, and if that results in our
setting DEAD (I think it does, assuming svc_tcp_state_change() is called
in that case), then the current code may have the effect of preventing
us from sending the reply.
I don't know if that's good or bad.
> So can we get rid of XPT_DEAL altogether?
OK, I also had another use in mind: for the purposes of 4.1 (which needs
to know when a connection goes down, e.g. to know that it's no longer
available for callbacks), I added a list of callbacks to the xprt,
called on svc_delete_xprt().
I just noticed that I think my current code allows the 4.1 code to
register an xprt after svc_delete_xprt() is called. I could fix that
race by checking for DEAD after trying to register.
(That callback code already seems messier than it should be, so maybe
someone else could suggest a better scheme. I'm stuck.
In any case, it wouldn't be so bad if that were the one remaining use of
DEAD.)
--b.
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