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Fixed flush condition when stale cycle valid/set indicators wrap around

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This commit is contained in:
Maria Matejka 2024-04-20 18:10:42 +02:00
parent 3685b0f9b6
commit 40061ac3ac
1 changed files with 56 additions and 3 deletions
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59
nest/rt-table.c
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@ -2721,10 +2721,63 @@ rt_prune_net(struct rtable_private *tab, struct network *n)
for (struct rte_storage *e = n->routes; e; e = e->next)
{
struct rt_import_hook *s = e->rte.sender;
if ((s->import_state == TIS_FLUSHING) ||
(e->rte.stale_cycle < s->stale_valid) ||
(e->rte.stale_cycle > s->stale_set))
_Bool stale = (s->import_state == TIS_FLUSHING);
if (!stale)
{
/*
* The range of 0..256 is split by s->stale_* like this:
*
* pruned pruning valid set
* | | | |
* 0 v v v v 256
* |...........................+++++++++++........|
*
* We want to drop everything outside the marked range, thus
* (e->rte.stale_cycle < s->stale_valid) ||
* (e->rte.stale_cycle > s->stale_set))
* looks right.
*
* But the pointers may wrap around, and in the following situation, all the routes get pruned:
*
* set pruned pruning valid
* | | | |
* 0 v v v v 256
* |++++++..................................++++++|
*
* In that case, we want
* (e->rte.stale_cycle > s->stale_valid) ||
* (e->rte.stale_cycle < s->stale_set))
*
* Full logic table:
*
* permutation | result | (S < V) + (S < SC) + (SC < V)
* -----------------+----------+---------------------------------
* SC < V <= S | prune | 0 + 0 + 1 = 1
* S < SC < V | prune | 1 + 1 + 1 = 3
* V <= S < SC | prune | 0 + 1 + 0 = 1
* SC <= S < V | keep | 1 + 0 + 1 = 2
* V <= SC <= S | keep | 0 + 0 + 0 = 0
* S < V <= SC | keep | 1 + 1 + 0 = 2
*
* Now the following code hopefully makes sense.
*/
int sv = (s->stale_set < s->stale_valid);
int ssc = (s->stale_set < e->rte.stale_cycle);
int scv = (e->rte.stale_cycle < s->stale_valid);
stale = (sv + ssc + scv) & 1;
}
/* By the C standard, either the importer is flushing and stale_perm is 1,
* or by the table above, stale_perm is between 0 and 3, where even values
* say "keep" and odd values say "prune". */
if (stale)
{
/* Announce withdrawal */
struct netindex *i = RTE_GET_NETINDEX(&e->rte);
rte_recalculate(tab, e->rte.sender, i, n, NULL, e->rte.src);
return 1;