From 4b55e86736d5b492cf689125da2600f59c7d2c39 Mon Sep 17 00:00:00 2001 From: Pedro Tammela Date: Mon, 11 Dec 2023 15:18:06 -0300 Subject: [PATCH 1/2] net/sched: act_api: rely on rcu in tcf_idr_check_alloc Instead of relying only on the idrinfo->lock mutex for bind/alloc logic, rely on a combination of rcu + mutex + atomics to better scale the case where multiple rtnl-less filters are binding to the same action object. Action binding happens when an action index is specified explicitly and an action exists which such index exists. Example: tc actions add action drop index 1 tc filter add ... matchall action drop index 1 tc filter add ... matchall action drop index 1 tc filter add ... matchall action drop index 1 tc filter ls ... filter protocol all pref 49150 matchall chain 0 filter protocol all pref 49150 matchall chain 0 handle 0x1 not_in_hw action order 1: gact action drop random type none pass val 0 index 1 ref 4 bind 3 filter protocol all pref 49151 matchall chain 0 filter protocol all pref 49151 matchall chain 0 handle 0x1 not_in_hw action order 1: gact action drop random type none pass val 0 index 1 ref 4 bind 3 filter protocol all pref 49152 matchall chain 0 filter protocol all pref 49152 matchall chain 0 handle 0x1 not_in_hw action order 1: gact action drop random type none pass val 0 index 1 ref 4 bind 3 When no index is specified, as before, grab the mutex and allocate in the idr the next available id. In this version, as opposed to before, it's simplified to store the -EBUSY pointer instead of the previous alloc + replace combination. When an index is specified, rely on rcu to find if there's an object in such index. If there's none, fallback to the above, serializing on the mutex and reserving the specified id. If there's one, it can be an -EBUSY pointer, in which case we just try again until it's an action, or an action. Given the rcu guarantees, the action found could be dead and therefore we need to bump the refcount if it's not 0, handling the case it's in fact 0. As bind and the action refcount are already atomics, these increments can happen without the mutex protection while many tcf_idr_check_alloc race to bind to the same action instance. In case binding encounters a parallel delete or add, it will return -EAGAIN in order to try again. Both filter and action apis already have the retry machinery in-place. In case it's an unlocked filter it retries under the rtnl lock. Signed-off-by: Pedro Tammela Acked-by: Jamal Hadi Salim Reviewed-by: Vlad Buslov Link: https://lore.kernel.org/r/20231211181807.96028-2-pctammela@mojatatu.com Signed-off-by: Jakub Kicinski --- net/sched/act_api.c | 65 ++++++++++++++++++++++++++++++--------------- 1 file changed, 43 insertions(+), 22 deletions(-) diff --git a/net/sched/act_api.c b/net/sched/act_api.c index 6611f292b6cb..076d5cdde656 100644 --- a/net/sched/act_api.c +++ b/net/sched/act_api.c @@ -816,6 +816,9 @@ EXPORT_SYMBOL(tcf_idr_cleanup); * its reference and bind counters, and return 1. Otherwise insert temporary * error pointer (to prevent concurrent users from inserting actions with same * index) and return 0. + * + * May return -EAGAIN for binding actions in case of a parallel add/delete on + * the requested index. */ int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index, @@ -824,43 +827,61 @@ int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index, struct tcf_idrinfo *idrinfo = tn->idrinfo; struct tc_action *p; int ret; + u32 max; -again: - mutex_lock(&idrinfo->lock); if (*index) { +again: + rcu_read_lock(); p = idr_find(&idrinfo->action_idr, *index); + if (IS_ERR(p)) { /* This means that another process allocated * index but did not assign the pointer yet. */ - mutex_unlock(&idrinfo->lock); + rcu_read_unlock(); goto again; } - if (p) { - refcount_inc(&p->tcfa_refcnt); - if (bind) - atomic_inc(&p->tcfa_bindcnt); - *a = p; - ret = 1; - } else { - *a = NULL; - ret = idr_alloc_u32(&idrinfo->action_idr, NULL, index, - *index, GFP_KERNEL); - if (!ret) - idr_replace(&idrinfo->action_idr, - ERR_PTR(-EBUSY), *index); + if (!p) { + /* Empty slot, try to allocate it */ + max = *index; + rcu_read_unlock(); + goto new; } + + if (!refcount_inc_not_zero(&p->tcfa_refcnt)) { + /* Action was deleted in parallel */ + rcu_read_unlock(); + return -EAGAIN; + } + + if (bind) + atomic_inc(&p->tcfa_bindcnt); + *a = p; + + rcu_read_unlock(); + + return 1; } else { + /* Find a slot */ *index = 1; - *a = NULL; - ret = idr_alloc_u32(&idrinfo->action_idr, NULL, index, - UINT_MAX, GFP_KERNEL); - if (!ret) - idr_replace(&idrinfo->action_idr, ERR_PTR(-EBUSY), - *index); + max = UINT_MAX; } + +new: + *a = NULL; + + mutex_lock(&idrinfo->lock); + ret = idr_alloc_u32(&idrinfo->action_idr, ERR_PTR(-EBUSY), index, max, + GFP_KERNEL); mutex_unlock(&idrinfo->lock); + + /* N binds raced for action allocation, + * retry for all the ones that failed. + */ + if (ret == -ENOSPC && *index == max) + ret = -EAGAIN; + return ret; } EXPORT_SYMBOL(tcf_idr_check_alloc); From 1dd7f18fc0ed75dad4d5f2ecc84f69c6b62b6a81 Mon Sep 17 00:00:00 2001 From: Pedro Tammela Date: Mon, 11 Dec 2023 15:18:07 -0300 Subject: [PATCH 2/2] net/sched: act_api: skip idr replace on bound actions tcf_idr_insert_many will replace the allocated -EBUSY pointer in tcf_idr_check_alloc with the real action pointer, exposing it to all operations. This operation is only needed when the action pointer is created (ACT_P_CREATED). For actions which are bound to (returned 0), the pointer already resides in the idr making such operation a nop. Even though it's a nop, it's still not a cheap operation as internally the idr code walks the idr and then does a replace on the appropriate slot. So if the action was bound, better skip the idr replace entirely. Signed-off-by: Pedro Tammela Acked-by: Jamal Hadi Salim Reviewed-by: Vlad Buslov Link: https://lore.kernel.org/r/20231211181807.96028-3-pctammela@mojatatu.com Signed-off-by: Jakub Kicinski --- include/net/act_api.h | 2 +- net/sched/act_api.c | 11 ++++++----- net/sched/cls_api.c | 2 +- 3 files changed, 8 insertions(+), 7 deletions(-) diff --git a/include/net/act_api.h b/include/net/act_api.h index 4ae0580b63ca..ea13e1e4a7c2 100644 --- a/include/net/act_api.h +++ b/include/net/act_api.h @@ -191,7 +191,7 @@ int tcf_idr_create_from_flags(struct tc_action_net *tn, u32 index, struct nlattr *est, struct tc_action **a, const struct tc_action_ops *ops, int bind, u32 flags); -void tcf_idr_insert_many(struct tc_action *actions[]); +void tcf_idr_insert_many(struct tc_action *actions[], int init_res[]); void tcf_idr_cleanup(struct tc_action_net *tn, u32 index); int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index, struct tc_action **a, int bind); diff --git a/net/sched/act_api.c b/net/sched/act_api.c index 076d5cdde656..3a7770eff52d 100644 --- a/net/sched/act_api.c +++ b/net/sched/act_api.c @@ -1304,7 +1304,7 @@ static const struct nla_policy tcf_action_policy[TCA_ACT_MAX + 1] = { [TCA_ACT_HW_STATS] = NLA_POLICY_BITFIELD32(TCA_ACT_HW_STATS_ANY), }; -void tcf_idr_insert_many(struct tc_action *actions[]) +void tcf_idr_insert_many(struct tc_action *actions[], int init_res[]) { struct tc_action *a; int i; @@ -1312,11 +1312,12 @@ void tcf_idr_insert_many(struct tc_action *actions[]) tcf_act_for_each_action(i, a, actions) { struct tcf_idrinfo *idrinfo; + if (init_res[i] == 0) /* Bound */ + continue; + idrinfo = a->idrinfo; mutex_lock(&idrinfo->lock); - /* Replace ERR_PTR(-EBUSY) allocated by tcf_idr_check_alloc if - * it is just created, otherwise this is just a nop. - */ + /* Replace ERR_PTR(-EBUSY) allocated by tcf_idr_check_alloc */ idr_replace(&idrinfo->action_idr, a, a->tcfa_index); mutex_unlock(&idrinfo->lock); } @@ -1516,7 +1517,7 @@ int tcf_action_init(struct net *net, struct tcf_proto *tp, struct nlattr *nla, /* We have to commit them all together, because if any error happened in * between, we could not handle the failure gracefully. */ - tcf_idr_insert_many(actions); + tcf_idr_insert_many(actions, init_res); *attr_size = tcf_action_full_attrs_size(sz); err = i - 1; diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c index 437daebc1fc4..dc1c19a25882 100644 --- a/net/sched/cls_api.c +++ b/net/sched/cls_api.c @@ -3313,7 +3313,7 @@ int tcf_exts_validate_ex(struct net *net, struct tcf_proto *tp, struct nlattr ** act->type = exts->type = TCA_OLD_COMPAT; exts->actions[0] = act; exts->nr_actions = 1; - tcf_idr_insert_many(exts->actions); + tcf_idr_insert_many(exts->actions, init_res); } else if (exts->action && tb[exts->action]) { int err;