Re: Antw: Re: [PATCH] iscsi_tcp set SO_LINGER to abort connection for error handling

2016-03-04 Thread Chris Leech 
On Fri, Mar 04, 2016 at 08:27:14AM +0100, Ulrich Windl wrote:
> Hi!
> 
> I always thought SO_LINGER only has an effect on connections that are
> (partially) closed only: So if there is some network outage on a TCP
> connection and the connection is still considered established, would
> it help?
> 
> Regards,
> Ulrich

It changes what happens during an active close. With SO_LINGER set,
close(2) will block until the connection is finalized or the l_linger
timeout is reached and the connection is aborted with a RST. The
important detail is that once close(2) returns, the (re)transmit queue
is purged, rather than being retried in the background.

- Chris

> 
> >>> Chris Leech  schrieb am 04.03.2016 um 06:00 in 
> >>> Nachricht
> <20160304050001.cohjmdvxyopzd...@straylight.hirudinean.org>:
> > On Thu, Mar 03, 2016 at 07:09:14PM -0600, Mike Christie wrote:
> >> On 03/03/2016 06:09 PM, Chris Leech wrote:
> >> > When requests are being failed it's important to abort the TCP
> >> > connection rather than let TCP wait and attempt a graceful shutdown.
> >> > 
> >> > That can be accomplished by setting the SO_LINGER socket option with a
> >> > linger time of 0 to drop queued data and close the connection with a RST
> >> > instead of a FIN.
> >> > 
> >> > Signed-off-by: Chris Leech 
> >> > ---
> >> >  usr/io.c | 15 +++
> >> >  1 file changed, 15 insertions(+)
> >> > 
> >> > diff --git a/usr/io.c b/usr/io.c
> >> > index f552e1e..48b233c 100644
> >> > --- a/usr/io.c
> >> > +++ b/usr/io.c
> >> > @@ -391,9 +391,24 @@ iscsi_io_tcp_poll(iscsi_conn_t *conn, int 
> >> > timeout_ms)
> >> >  void
> >> >  iscsi_io_tcp_disconnect(iscsi_conn_t *conn)
> >> >  {
> >> > +struct linger so_linger = { .l_onoff = 1, .l_linger = 0 };
> >> > +
> >> >  if (conn->socket_fd >= 0) {
> >> >  log_debug(1, "disconnecting conn %p, fd %d", conn,
> >> >   conn->socket_fd);
> >> > +
> >> > +/* If the state is not IN_LOGOUT, this isn't a clean 
> >> > shutdown
> >> > + * and there's some sort of error handling going on. In 
> >> > that
> >> > + * case, set a 0 SO_LINGER to force an abortive close 
> >> > (RST) and
> >> > + * free whatever is sitting in the TCP transmit queue. 
> >> > This is
> >> > + * done to prevent stale data from being sent should the
> >> > + * network connection be restored before TCP times out.
> >> > + */
> >> > +if (conn->state != ISCSI_CONN_STATE_IN_LOGOUT) {
> >> > +setsockopt(conn->socket_fd, SOL_SOCKET, 
> >> > SO_LINGER,
> >> > +   _linger, sizeof(so_linger));
> >> > +}
> >> > +
> >> >  close(conn->socket_fd);
> >> >  conn->socket_fd = -1;
> >> >  }
> >> > 
> >> 
> >> Nice.
> >> 
> >> For maybe a slightly different problem, but hoping I get lucky and your
> >> patch fixes it too, I thought the network layer was still accessing
> >> pages that we tried to send and was causing a oops. I get the part where
> >> with your patch the network layer will not try to send data anymore, but
> >> I guess I am asking if the network layer could still be doing some sort
> >> of delayed cleanup process after close() has returned?
> > 
> > From what I can tell in the tcp code, the zero linger handling purges
> > all of the socket queues freeing everything before close returns.
> > 
> > - Chris

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Antw: Re: [PATCH] iscsi_tcp set SO_LINGER to abort connection for error handling

2016-03-03 Thread Ulrich Windl 
Hi!

I always thought SO_LINGER only has an effect on connections that are 
(partially) closed only: So if there is some network outage on a TCP connection 
and the connection is still considered established, would it help?

Regards,
Ulrich

>>> Chris Leech  schrieb am 04.03.2016 um 06:00 in Nachricht
<20160304050001.cohjmdvxyopzd...@straylight.hirudinean.org>:
> On Thu, Mar 03, 2016 at 07:09:14PM -0600, Mike Christie wrote:
>> On 03/03/2016 06:09 PM, Chris Leech wrote:
>> > When requests are being failed it's important to abort the TCP
>> > connection rather than let TCP wait and attempt a graceful shutdown.
>> > 
>> > That can be accomplished by setting the SO_LINGER socket option with a
>> > linger time of 0 to drop queued data and close the connection with a RST
>> > instead of a FIN.
>> > 
>> > Signed-off-by: Chris Leech 
>> > ---
>> >  usr/io.c | 15 +++
>> >  1 file changed, 15 insertions(+)
>> > 
>> > diff --git a/usr/io.c b/usr/io.c
>> > index f552e1e..48b233c 100644
>> > --- a/usr/io.c
>> > +++ b/usr/io.c
>> > @@ -391,9 +391,24 @@ iscsi_io_tcp_poll(iscsi_conn_t *conn, int timeout_ms)
>> >  void
>> >  iscsi_io_tcp_disconnect(iscsi_conn_t *conn)
>> >  {
>> > +  struct linger so_linger = { .l_onoff = 1, .l_linger = 0 };
>> > +
>> >if (conn->socket_fd >= 0) {
>> >log_debug(1, "disconnecting conn %p, fd %d", conn,
>> > conn->socket_fd);
>> > +
>> > +  /* If the state is not IN_LOGOUT, this isn't a clean shutdown
>> > +   * and there's some sort of error handling going on. In that
>> > +   * case, set a 0 SO_LINGER to force an abortive close (RST) and
>> > +   * free whatever is sitting in the TCP transmit queue. This is
>> > +   * done to prevent stale data from being sent should the
>> > +   * network connection be restored before TCP times out.
>> > +   */
>> > +  if (conn->state != ISCSI_CONN_STATE_IN_LOGOUT) {
>> > +  setsockopt(conn->socket_fd, SOL_SOCKET, SO_LINGER,
>> > + _linger, sizeof(so_linger));
>> > +  }
>> > +
>> >close(conn->socket_fd);
>> >conn->socket_fd = -1;
>> >}
>> > 
>> 
>> Nice.
>> 
>> For maybe a slightly different problem, but hoping I get lucky and your
>> patch fixes it too, I thought the network layer was still accessing
>> pages that we tried to send and was causing a oops. I get the part where
>> with your patch the network layer will not try to send data anymore, but
>> I guess I am asking if the network layer could still be doing some sort
>> of delayed cleanup process after close() has returned?
> 
> From what I can tell in the tcp code, the zero linger handling purges
> all of the socket queues freeing everything before close returns.
> 
> - Chris
> 
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