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BUG/MEDIUM: list: add missing store barriers when updating elements and head

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Commit a8434ec14 ("MINOR: lists: Implement locked variations.")
introduced locked lists which use the elements pointers as locks
for concurrent operations. Under heavy stress the lists occasionally
fail. The cause is a missing barrier at some points when updating
the list element and the head : nothing prevents the compiler (or
CPU) from updating the list head first before updating the element,
making another thread jump to a wrong location. This patch simply
adds the missing barriers before these two opeations.

This will have to be backported if the commit above is backported.
This commit is contained in:
Willy Tarreau 2019-02-28 11:14:22 +01:00
parent 285192564d
commit 690d2ad4d2
1 changed files with 5 additions and 0 deletions
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5
include/common/mini-clist.h
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@ -189,6 +189,7 @@ struct cond_wordlist {
} \
(el)->n = n; \
(el)->p = p; \
__ha_barrier_store(); \
n->p = (el); \
__ha_barrier_store(); \
p->n = (el); \
@ -214,6 +215,7 @@ struct cond_wordlist {
} \
(el)->n = n; \
(el)->p = p; \
__ha_barrier_store(); \
n->p = (el); \
__ha_barrier_store(); \
p->n = (el); \
@ -276,6 +278,7 @@ struct cond_wordlist {
continue; \
if (n == (lh)) { \
(lh)->n = lh; \
__ha_barrier_store(); \
_ret = NULL; \
break; \
} \
@ -288,6 +291,7 @@ struct cond_wordlist {
n2 = HA_ATOMIC_XCHG(&n->n, LLIST_BUSY); \
if (n2 == LLIST_BUSY) { \
n->p = p; \
__ha_barrier_store(); \
(lh)->n = n; \
__ha_barrier_store(); \
continue; \
@ -296,6 +300,7 @@ struct cond_wordlist {
if (p2 == LLIST_BUSY) { \
n->n = n2; \
n->p = p; \
__ha_barrier_store(); \
(lh)->n = n; \
__ha_barrier_store(); \
continue; \