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ipmr: remove hard code cache_resolve_queue_len limit

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This is a re-post of previous patch wrote by David Miller[1].

Phil Karn reported[2] that on busy networks with lots of unresolved
multicast routing entries, the creation of new multicast group routes
can be extremely slow and unreliable.

The reason is we hard-coded multicast route entries with unresolved source
addresses(cache_resolve_queue_len) to 10. If some multicast route never
resolves and the unresolved source addresses increased, there will
be no ability to create new multicast route cache.

To resolve this issue, we need either add a sysctl entry to make the
cache_resolve_queue_len configurable, or just remove cache_resolve_queue_len
limit directly, as we already have the socket receive queue limits of mrouted
socket, pointed by David.

>From my side, I'd perfer to remove the cache_resolve_queue_len limit instead
of creating two more(IPv4 and IPv6 version) sysctl entry.

[1] https://lkml.org/lkml/2018/7/22/11
[2] https://lkml.org/lkml/2018/7/21/343

v3: instead of remove cache_resolve_queue_len totally, let's only remove
the hard code limit when allocate the unresolved cache, as Eric Dumazet
suggested, so we don't need to re-count it in other places.

v2: hold the mfc_unres_lock while walking the unresolved list in
queue_count(), as Nikolay Aleksandrov remind.

Reported-by: Phil Karn <karn@ka9q.net>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Hangbin Liu 2019-09-06 15:36:01 +08:00 committed by David S. Miller
parent 06be463368
commit 0079ad8e8d
2 changed files with 4 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
net/ipv4/ipmr.c
View File

@ -1134,8 +1134,8 @@ static int ipmr_cache_unresolved(struct mr_table *mrt, vifi_t vifi,
if (!found) {
/* Create a new entry if allowable */
if (atomic_read(&mrt->cache_resolve_queue_len) >= 10 ||
(c = ipmr_cache_alloc_unres()) == NULL) {
c = ipmr_cache_alloc_unres();
if (!c) {
spin_unlock_bh(&mfc_unres_lock);
kfree_skb(skb);

4
net/ipv6/ip6mr.c
View File

@ -1148,8 +1148,8 @@ static int ip6mr_cache_unresolved(struct mr_table *mrt, mifi_t mifi,
* Create a new entry if allowable
*/
if (atomic_read(&mrt->cache_resolve_queue_len) >= 10 ||
(c = ip6mr_cache_alloc_unres()) == NULL) {
c = ip6mr_cache_alloc_unres();
if (!c) {
spin_unlock_bh(&mfc_unres_lock);
kfree_skb(skb);