On Fri, Feb 4, 2022 at 8:37 AM Adrian Moreno <amore...@redhat.com> wrote: > > > > On 1/18/22 16:01, Peng He wrote: > > From hepeng: > > https://patchwork.ozlabs.org/project/openvswitch/patch/20200717015041.82746-1-hepeng.0...@bytedance.com/#2487473 > > > > also from guohongzhi <guohongz...@huawei.com>: > > http://patchwork.ozlabs.org/project/openvswitch/patch/20200306130555.19884-1-guohongz...@huawei.com/ > > > > also from a discussion about the mixing use of RCU and refcount in the mail > > list with Ilya Maximets, William Tu, Ben Pfaf, and Gaëtan Rivet. > > > > A summary, as quoted from Ilya: > > > > " > > RCU for ofproto was introduced for one > > and only one reason - to avoid freeing ofproto while rules are still > > alive. This was done in commit f416c8d61601 ("ofproto: RCU postpone > > rule destruction."). The goal was to allow using rules without > > refcounting them within a single grace period. And that forced us > > to postpone destruction of the ofproto for a single grace period. > > Later commit 39c9459355b6 ("Use classifier versioning.") made it > > possible for rules to be alive for more than one grace period, so > > the commit made ofproto wait for 2 grace periods by double postponing. > > As we can see now, that wasn't enough and we have to wait for more > > than 2 grace periods in certain cases. > > " > > > > In a short, the ofproto should have a longer life time than rule, if > > the rule lasts for more than 2 grace periods, the ofproto should live > > longer to ensure rule->ofproto is valid. It's hard to predict how long > > a ofproto should live, thus we need to use refcount on ofproto to make > > things easy. The controversial part is that we have already used RCU > > postpone > > to delay ofproto destrution, if we have to add refcount, is it simpler to > > use just refcount without RCU postpone? > > > > IMO, I think going back to the pure refcount solution is more > > complicated than mixing using both. > > > > Gaëtan Rive asks some questions on guohongzhi's v2 patch: > > > > during ofproto_rule_create, should we use ofproto_ref > > or ofproto_try_ref? how can we make sure the ofproto is alive? > > > > By using RCU, ofproto has three states: > > > > state 1: alive, with refcount >= 1 > > state 2: dying, with refcount == 0, however pointer is valid > > state 3: died, memory freed, pointer might be dangling. > > > > Without using RCU, there is no state 2, thus, we have to be very careful > > every time we see a ofproto pointer. In contrast, with RCU, we can be sure > > that it's alive at least in this grace peroid, so we can just check if > > it is dying by ofproto_try_ref. > > > > This shows that by mixing use of RCU and refcount we can save a lot of work > > worrying if ofproto is dangling. > > > > In short, the RCU part makes sure the ofproto is alive when we use it, > > and the refcount part makes sure it lives longer enough. > > > > Also regarding a new patch filed recently, people are now making use > > of RCU to protect ofproto: > > > > https://patchwork.ozlabs.org/project/openvswitch/patch/1638530715-44436-1-git-send-email-wangyunj...@huawei.com/ > > > > In this patch, I have merged guohongzhi's patch and mine, and fixes > > accoring to the previous comments. > > > > Signed-off-by: Peng He <hepeng.0...@bytedance.com> > > Signed-off-by: guohongzhi <guohongz...@huawei.com> > > --- > > ofproto/ofproto-dpif-xlate-cache.c | 2 + > > ofproto/ofproto-dpif-xlate.c | 14 ++++--- > > ofproto/ofproto-dpif.c | 24 +++++++----- > > ofproto/ofproto-provider.h | 2 + > > ofproto/ofproto.c | 62 +++++++++++++++++++++++++++--- > > ofproto/ofproto.h | 4 ++ > > 6 files changed, 87 insertions(+), 21 deletions(-) > > > > diff --git a/ofproto/ofproto-dpif-xlate-cache.c > > b/ofproto/ofproto-dpif-xlate-cache.c > > index dcc91cb38..9224ee2e6 100644 > > --- a/ofproto/ofproto-dpif-xlate-cache.c > > +++ b/ofproto/ofproto-dpif-xlate-cache.c > > @@ -209,6 +209,7 @@ xlate_cache_clear_entry(struct xc_entry *entry) > > { > > switch (entry->type) { > > case XC_TABLE: > > + ofproto_unref(&(entry->table.ofproto->up)); > > break; > > case XC_RULE: > > ofproto_rule_unref(&entry->rule->up); > > @@ -231,6 +232,7 @@ xlate_cache_clear_entry(struct xc_entry *entry) > > free(entry->learn.ofm); > > break; > > case XC_NORMAL: > > + ofproto_unref(&(entry->normal.ofproto->up)); > > break; > > case XC_FIN_TIMEOUT: > > /* 'u.fin.rule' is always already held as a XC_RULE, which > > diff --git a/ofproto/ofproto-dpif-xlate.c b/ofproto/ofproto-dpif-xlate.c > > index 6fb59e170..129cdf714 100644 > > --- a/ofproto/ofproto-dpif-xlate.c > > +++ b/ofproto/ofproto-dpif-xlate.c > > @@ -3024,12 +3024,14 @@ xlate_normal(struct xlate_ctx *ctx) > > struct xc_entry *entry; > > > > /* Save just enough info to update mac learning table later. */ > > - entry = xlate_cache_add_entry(ctx->xin->xcache, XC_NORMAL); > > - entry->normal.ofproto = ctx->xbridge->ofproto; > > - entry->normal.in_port = flow->in_port.ofp_port; > > - entry->normal.dl_src = flow->dl_src; > > - entry->normal.vlan = vlan; > > - entry->normal.is_gratuitous_arp = is_grat_arp; > > + if (ofproto_try_ref(&ctx->xbridge->ofproto->up)) { > > + entry = xlate_cache_add_entry(ctx->xin->xcache, XC_NORMAL); > > + entry->normal.ofproto = ctx->xbridge->ofproto; > > + entry->normal.in_port = flow->in_port.ofp_port; > > + entry->normal.dl_src = flow->dl_src; > > + entry->normal.vlan = vlan; > > + entry->normal.is_gratuitous_arp = is_grat_arp; > > + } > > } > > > > /* Determine output bundle. */ > > diff --git a/ofproto/ofproto-dpif.c b/ofproto/ofproto-dpif.c > > index 8143dd965..c0a87456a 100644 > > --- a/ofproto/ofproto-dpif.c > > +++ b/ofproto/ofproto-dpif.c > > @@ -4471,12 +4471,14 @@ rule_dpif_lookup_from_table(struct ofproto_dpif > > *ofproto, > > atomic_add_relaxed(&tbl->n_matched, stats->n_packets, > > &orig); > > } > > if (xcache) { > > - struct xc_entry *entry; > > + if (ofproto_try_ref(&ofproto->up)) { > > + struct xc_entry *entry; > > > > - entry = xlate_cache_add_entry(xcache, XC_TABLE); > > - entry->table.ofproto = ofproto; > > - entry->table.id = *table_id; > > - entry->table.match = true; > > + entry = xlate_cache_add_entry(xcache, XC_TABLE); > > + entry->table.ofproto = ofproto; > > + entry->table.id = *table_id; > > + entry->table.match = true; > > + } > > } > > return rule; > > } > > @@ -4507,12 +4509,14 @@ rule_dpif_lookup_from_table(struct ofproto_dpif > > *ofproto, > > stats->n_packets, &orig); > > } > > if (xcache) { > > - struct xc_entry *entry; > > + if (ofproto_try_ref(&ofproto->up)) { > > + struct xc_entry *entry; > > > > - entry = xlate_cache_add_entry(xcache, XC_TABLE); > > - entry->table.ofproto = ofproto; > > - entry->table.id = next_id; > > - entry->table.match = (rule != NULL); > > + entry = xlate_cache_add_entry(xcache, XC_TABLE); > > + entry->table.ofproto = ofproto; > > + entry->table.id = next_id; > > + entry->table.match = (rule != NULL); > > + } > > } > > if (rule) { > > goto out; /* Match. */ > > diff --git a/ofproto/ofproto-provider.h b/ofproto/ofproto-provider.h > > index 14b909973..ed10b8c76 100644 > > --- a/ofproto/ofproto-provider.h > > +++ b/ofproto/ofproto-provider.h > > @@ -143,6 +143,8 @@ struct ofproto { > > /* Variable length mf_field mapping. Stores all configured variable > > length > > * meta-flow fields (struct mf_field) in a switch. */ > > struct vl_mff_map vl_mff_map; > > + /* refcount to this ofproto, holds by rule/group/xlate_caches */ > > + struct ovs_refcount refcount; > > }; > > > > void ofproto_init_tables(struct ofproto *, int n_tables); > > diff --git a/ofproto/ofproto.c b/ofproto/ofproto.c > > index 56aeac720..10a22d9ec 100644 > > --- a/ofproto/ofproto.c > > +++ b/ofproto/ofproto.c > > @@ -549,6 +549,7 @@ ofproto_create(const char *datapath_name, const char > > *datapath_type, > > > > ovs_mutex_init(&ofproto->vl_mff_map.mutex); > > cmap_init(&ofproto->vl_mff_map.cmap); > > + ovs_refcount_init(&ofproto->refcount); > > > > error = ofproto->ofproto_class->construct(ofproto); > > if (error) { > > @@ -1695,9 +1696,24 @@ ofproto_destroy__(struct ofproto *ofproto) > > ofproto->ofproto_class->dealloc(ofproto); > > } > > > > -/* Destroying rules is doubly deferred, must have 'ofproto' around for > > them. > > - * - 1st we defer the removal of the rules from the classifier > > - * - 2nd we defer the actual destruction of the rules. */ > > +/* We used to use defer function to wait for two grace periods > > + * as we assume the rule that holds the ofproto pointer will > > + * live at most two grace period. Howvever, we found at certain > > + * cases, this assumption does not stand. > > + * > > + * destroying a rule may have to wait multiple grace periods: > > + * remove_rules_postponed (one grace period) > > + * -> remove_rule_rcu > > + * -> remove_rule_rcu__ > > + * -> ofproto_rule_unref -> ref count != 1 > > + * -> ... more grace periods. > > + * -> rule_destroy_cb (> 2 grace periods) > > + * -> free > > + * > > + * So we have to check the refcount for sure all the rules > > + * have been destroyed. > > + * > > + */ > > static void > > ofproto_destroy_defer__(struct ofproto *ofproto) > > OVS_EXCLUDED(ofproto_mutex) > > @@ -1705,6 +1721,26 @@ ofproto_destroy_defer__(struct ofproto *ofproto) > > ovsrcu_postpone(ofproto_destroy__, ofproto); > > } > > > > +void > > +ofproto_ref(struct ofproto *ofproto) > > +{ > > + ovs_refcount_ref(&ofproto->refcount); > > +} > > + > > +bool > > +ofproto_try_ref(struct ofproto *ofproto) > > +{ > > + return ovs_refcount_try_ref_rcu(&ofproto->refcount); > > +} > > + > > +void > > +ofproto_unref(struct ofproto *ofproto) > > +{ > > + if (ofproto && ovs_refcount_unref(&ofproto->refcount) == 1) { > > + ovsrcu_postpone(ofproto_destroy_defer__, ofproto); > > + } > > +} > > + > > void > > ofproto_destroy(struct ofproto *p, bool del) > > OVS_EXCLUDED(ofproto_mutex) > > @@ -1736,8 +1772,7 @@ ofproto_destroy(struct ofproto *p, bool del) > > p->connmgr = NULL; > > ovs_mutex_unlock(&ofproto_mutex); > > > > - /* Destroying rules is deferred, must have 'ofproto' around for them. > > */ > > - ovsrcu_postpone(ofproto_destroy_defer__, p); > > + ofproto_unref(p); > > } > > > > /* Destroys the datapath with the respective 'name' and 'type'. With the > > Linux > > @@ -2929,6 +2964,10 @@ ofproto_rule_destroy__(struct rule *rule) > > cls_rule_destroy(CONST_CAST(struct cls_rule *, &rule->cr)); > > rule_actions_destroy(rule_get_actions(rule)); > > ovs_mutex_destroy(&rule->mutex); > > + /* we need to call ofproto_unref first, and thanks to rcu, ofproto is > > alive > > + * otherwise, group is freed, group->ofproto is invalid > > + */ > > + ofproto_unref(rule->ofproto); > > rule->ofproto->ofproto_class->rule_dealloc(rule); > > } > > > > @@ -3069,6 +3108,10 @@ group_destroy_cb(struct ofgroup *group) > > &group->props)); > > ofputil_bucket_list_destroy(CONST_CAST(struct ovs_list *, > > &group->buckets)); > > + /* we need to call ofproto_unref first, and thanks to rcu, ofproto is > > alive > > + * otherwise, group is freed, group->ofproto is invalid > > + */ > > + ofproto_unref(group->ofproto); > > group->ofproto->ofproto_class->group_dealloc(group); > > } > > > > @@ -5279,6 +5322,11 @@ ofproto_rule_create(struct ofproto *ofproto, struct > > cls_rule *cr, > > return OFPERR_OFPFMFC_UNKNOWN; > > } > > > > + if (!ofproto_try_ref(ofproto)) { > > + cls_rule_destroy(cr); > > + return OFPERR_OFPFMFC_UNKNOWN; > > + } > > + > > /* Initialize base state. */ > > *CONST_CAST(struct ofproto **, &rule->ofproto) = ofproto; > > cls_rule_move(CONST_CAST(struct cls_rule *, &rule->cr), cr); > > @@ -7345,6 +7393,10 @@ init_group(struct ofproto *ofproto, const struct > > ofputil_group_mod *gm, > > return OFPERR_OFPGMFC_OUT_OF_GROUPS; > > } > > > > + if (!ofproto_try_ref(ofproto)) { > > + return OFPERR_OFPFMFC_UNKNOWN; > > + } > > + > > *CONST_CAST(struct ofproto **, &(*ofgroup)->ofproto) = ofproto; > > *CONST_CAST(uint32_t *, &((*ofgroup)->group_id)) = gm->group_id; > > *CONST_CAST(enum ofp11_group_type *, &(*ofgroup)->type) = gm->type; > > diff --git a/ofproto/ofproto.h b/ofproto/ofproto.h > > index b0262da2d..4e15167ab 100644 > > --- a/ofproto/ofproto.h > > +++ b/ofproto/ofproto.h > > @@ -563,6 +563,10 @@ int ofproto_port_get_cfm_status(const struct ofproto *, > > enum ofputil_table_miss ofproto_table_get_miss_config(const struct > > ofproto *, > > uint8_t table_id); > > > > +void ofproto_ref(struct ofproto *); > > +void ofproto_unref(struct ofproto *); > > +bool ofproto_try_ref(struct ofproto *); > > + > > #ifdef __cplusplus > > } > > #endif > > > Hi Peng, > > Do we still to protect the reference that "struct upcall" holds? i.e: > https://patchwork.ozlabs.org/project/openvswitch/patch/1638530715-44436-1-git-send-email-wangyunj...@huawei.com/
I think that patch is also needed, in addition to this one. -M > Thanks. > -- > Adrián Moreno > > _______________________________________________ > dev mailing list > d...@openvswitch.org > https://mail.openvswitch.org/mailman/listinfo/ovs-dev _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev
