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BUG/MEDIUM: h2: make sure the last stream closes the connection after a timeout

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If a timeout strikes on the connection side with some active streams,
there is a corner case which can sometimes cause the following sequence
to happen :

  - There are active streams but there are data in the mux buffer
    (eg: a client suddenly disconnected during a download with pending
    requests). The timeout is active.

  - The timeout strikes, h2_timeout_task() is called, kills the task and
    doesn't close the connection since there are streams left ; The
    connection is marked in H2_CS_ERROR ;

  - the streams are woken up and closed ;

  - when the last stream closes, calling h2_detach(), it sees the
    tree list is empty, but there is no condition allowing the
    connection to be closed (mbuf->o > 0), thus it does nothing ;

  - since the task is dead, there's no more hope to clear this
    situation later

For now we can take care of this by adding a test for the presence of
H2_CS_ERROR and !task, implying the timeout task triggered already
and will not be able to handle this again.

Over the long term it seems like a more reliable test on should be
made, so that it is possible to know whether or not someone is still
able to close this connection.

A big thanks to Janusz Dziemidowicz and Milan Petruzelka for providing
many details helping in figuring this bug.
This commit is contained in:
Willy Tarreau 2018-06-13 14:24:56 +02:00
parent 00610960a1
commit 42d55b9b6a
1 changed files with 1 additions and 0 deletions
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1
src/mux_h2.c
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@ -2493,6 +2493,7 @@ static void h2_detach(struct conn_stream *cs)
*/
if (eb_is_empty(&h2c->streams_by_id) && /* don't close if streams exist */
((h2c->conn->flags & CO_FL_ERROR) || /* errors close immediately */
(h2c->st0 >= H2_CS_ERROR && !h2c->task) || /* a timeout stroke earlier */
(h2c->flags & H2_CF_GOAWAY_FAILED) ||
(!h2c->mbuf->o && /* mux buffer empty, also process clean events below */
(conn_xprt_read0_pending(h2c->conn) ||