Re: [linux-cifs-client] [PATCH] get rid of spurious session reconnects

[Steve French]

Merged into cifs-2.6.git

I still want to review/test more on the one other bug fix (quota or
out of disk space, cifs sync issue which Jeff proposed a fix for
earlier) and the ASCII vs. Unicode plain-text password check bug

On Nov 19, 2007 8:47 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> On Mon, 19 Nov 2007 14:23:13 +0100
> Petr Tesarik <ptesarik@xxxxxxx> wrote:
>
> > On Mon, 2007-11-19 at 06:42 -0500, Jeff Layton wrote:
> > > On Mon, 19 Nov 2007 10:30:45 +0100
> > > Petr Tesarik <ptesarik@xxxxxxx> wrote:
> > >
> > > > Hi,
> > > >
> > > > while merging commits f01d5e14e764b14b6bf5512678523d009254b209 and
> > > > 638b250766272fcaaa0f7ed2776f58f4ac701914 into SLES10, I've noticed
> > > > that there's apparently a bug. The code currently looks like this:
> > > >
> > > >           pdu_length = 4; /* enough to get RFC1001 header */
> > > > incomplete_rcv:
> > > >           length =
> > > >               kernel_recvmsg(csocket, &smb_msg,
> > > >                           &iov, 1, pdu_length, 0 /* BB other
> > > > flags? */);
> > > >
> > > > /* ... some irrelevant code left out ... */
> > > >
> > > >           } else if (length < 4) {        /* <----- HERE IS
> > > > THE PROBLEM cFYI(1, ("less than four bytes received (%d bytes)",
> > > >                         length));
> > > >                   pdu_length -= length;
> > > >                   msleep(1);
> > > >                   goto incomplete_rcv;
> > > >           }
> > > >
> > > > I think we should be checking for length < pdu_length, not for
> > > > length < 4, because if we read 2 bytes in the first run and 2
> > > > bytes in the second un, CIFS will still treat the second run as
> > > > incomplete (and possibly run in an infinite loop). Am I missing
> > > > something obvious?
> > > >
> > >
> > > I think you're right that the logic there is wrong, but I don't see
> > > an infinite loop happening. It looks like in this situation, that
> > > the next call to kernel_recvmsg will be called a size of 0, which
> > > should eventually return 0. It'll then fall into the previous
> > > condition -- do a reconnect and then go around the big loop again.
> > >
> > > A patch to clean that up would probably be a good thing. We likely
> > > don't need to do a reconnect here.
> >
> > OK, here we go:
> >
> > When retrying kernel_recvmsg() because of a short read, check returned
> > length against the remaining length, not against total length. This
> > avoids unneeded session reconnects which would otherwise occur when
> > kernel_recvmsg() finally returns zero when asked to read zero bytes.
> >
> > Signed-off-by: Petr Tesarik <ptesarik@xxxxxxx>
> >
>
> Looks good (nice catch on this problem, btw). How about we fix up the
> cFYI at the same time? Note that this should probably be tested, even
> though it seems logical.
>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
>
> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> index c4b32b7..b6ed933 100644
> --- a/fs/cifs/connect.c
> +++ b/fs/cifs/connect.c
> @@ -438,9 +438,9 @@ incomplete_rcv:
>                         csocket = server->ssocket;
>                         wake_up(&server->response_q);
>                         continue;
> -               } else if (length < 4) {
> -                       cFYI(1, ("less than four bytes received (%d bytes)",
> -                             length));
> +               } else if (length < pdu_length) {
> +                       cFYI(1, ("less than %d bytes received (%d bytes)",
> +                             pdu_length, length));
>                         pdu_length -= length;
>                         msleep(1);
>                         goto incomplete_rcv;
>



-- 
Thanks,

Steve
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