commit 982bf2a0481648a0885b100cc565add399762028
Author: Olivier Houchard <ohouchard@haproxy.com>
Date:   Tue Feb 26 18:46:07 2019 +0100

    BUG/MEDIUM: lists: Properly handle the case we're removing the first elt.
    
    In LIST_DEL_LOCKED(), initialize p2 to NULL, and only attempt to set it back
    to its previous value if we had a previous element, and thus p2 is non-NULL.
    
    (cherry picked from commit db64489aac2135c6ceceec47fe98dc42c0558466)
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    (cherry picked from commit a3d6a2b9dac9775c55a10ed6b60deca219f06ff6)
    Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>

diff --git a/include/common/mini-clist.h b/include/common/mini-clist.h
index b3f396ef..aebeec38 100644
--- a/include/common/mini-clist.h
+++ b/include/common/mini-clist.h
@@ -226,7 +226,7 @@ struct cond_wordlist {
 	do {                                                               \
 		while (1) {                                                \
 			struct list *n, *n2;                               \
-			struct list *p, *p2;                               \
+			struct list *p, *p2 = NULL;                        \
 			n = HA_ATOMIC_XCHG(&(el)->n, LLIST_BUSY);          \
 			if (n == LLIST_BUSY)                               \
 			        continue;                                  \
@@ -248,7 +248,8 @@ struct cond_wordlist {
 			if (n != (el)) {                                   \
 			        n2 = HA_ATOMIC_XCHG(&n->p, LLIST_BUSY);    \
 				if (n2 == LLIST_BUSY) {                    \
-					p2->n = (el);                      \
+					if (p2 != NULL)                    \
+						p2->n = (el);              \
 					(el)->p = p;                       \
 					(el)->n = n;                       \
 					__ha_barrier_store();              \