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BUG/MAJOR: mux-h2: do not add a stream twice to the send list

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In this long thread, Maciej Zdeb reported that the H2 mux was still
going through endless loops from time to time :

  https://www.mail-archive.com/haproxy@formilux.org/msg33709.html

What happens is the following :
- in h2s_frt_make_resp_data() we can set H2_SF_BLK_SFCTL and remove the
  stream from the send_list
- then in h2_shutr() and h2_shutw(), we check if the list is empty before
  subscribing the element, which is true after the case above
- then in h2c_update_all_ws() we still have H2_SF_BLK_SFCTL with the item
  in the send_list, thus LIST_ADDQ() adds it a second time.

This patch adds a check of list emptiness before performing the LIST_ADDQ()
when the flow control window opens. Maciej reported that it reliably fixed
the problem for him.

As later discussed with Olivier, this fixes the consequence of the issue
rather than its cause. The root cause is that a stream should never be in
the send_list with a blocking flag set and the various places that can lead
to this situation must be revisited. Thus another fix is expected soon for
this issue, which will require some observation. In the mean time this one
is easy enough to validate and to backport.

Many thanks to Maciej for testing several versions of the patch, each
time providing detailed traces which allowed to nail the problem down.

This patch must be backported to 1.9.
This commit is contained in:
Willy Tarreau 2019-05-13 08:05:28 +02:00
parent 6a38b3297c
commit 4087346dab
1 changed files with 2 additions and 4 deletions
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6
src/mux_h2.c
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@ -1498,9 +1498,8 @@ static void h2c_update_all_ws(struct h2c *h2c, int diff)
if (h2s->mws > 0 && (h2s->flags & H2_SF_BLK_SFCTL)) {
h2s->flags &= ~H2_SF_BLK_SFCTL;
if (h2s->send_wait)
if (h2s->send_wait && LIST_ISEMPTY(&h2s->list))
LIST_ADDQ(&h2c->send_list, &h2s->list);
}
node = eb32_next(node);
@ -1805,9 +1804,8 @@ static int h2c_handle_window_update(struct h2c *h2c, struct h2s *h2s)
h2s->mws += inc;
if (h2s->mws > 0 && (h2s->flags & H2_SF_BLK_SFCTL)) {
h2s->flags &= ~H2_SF_BLK_SFCTL;
if (h2s->send_wait)
if (h2s->send_wait && LIST_ISEMPTY(&h2s->list))
LIST_ADDQ(&h2c->send_list, &h2s->list);
}
}
else {