commit d6c19ac2c0458445e521fd08eded304c26eecfe7
Author: Willy Tarreau <w@1wt.eu>
Date:   Fri Jan 10 18:20:15 2020 +0100

    BUG/MEDIUM: mux-h2: fix missing test on sending_list in previous patch
    
    Previous commit 989539b048 ("BUG/MINOR: mux-h2: use a safe
    list_for_each_entry in h2_send()") accidently lost its sending_list test,
    resulting in some elements to be woken up again while already in the
    sending_list and h2_unsubscribe() crashing on integrity tests (only
    when built with DEBUG_DEV).
    
    If the fix above is backported this one must be as well.
    
    (cherry picked from commit 70c5b0e5fd5ad243f4645b37a0f89068de97e90e)
    Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>

diff --git a/src/mux_h2.c b/src/mux_h2.c
index 92a50da24..d46a316ac 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -3265,6 +3265,10 @@ static void h2_resume_each_sending_h2s(struct h2c *h2c, struct list *head)
 			break;
 
 		h2s->flags &= ~H2_SF_BLK_ANY;
+
+		if (LIST_ADDED(&h2s->sending_list))
+			continue;
+
 		/* For some reason, the upper layer failed to subscribe again,
 		 * so remove it from the send_list
 		 */