From patchwork Tue Dec 5 15:30:11 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pedro Tammela X-Patchwork-Id: 13480331 X-Patchwork-Delegate: kuba@kernel.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mojatatu-com.20230601.gappssmtp.com header.i=@mojatatu-com.20230601.gappssmtp.com header.b="oLMD5nEf" Received: from mail-pl1-x62c.google.com (mail-pl1-x62c.google.com [IPv6:2607:f8b0:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 36A3DA9 for ; Tue, 5 Dec 2023 07:30:31 -0800 (PST) Received: by mail-pl1-x62c.google.com with SMTP id d9443c01a7336-1cf7a8ab047so23265645ad.1 for ; Tue, 05 Dec 2023 07:30:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mojatatu-com.20230601.gappssmtp.com; s=20230601; t=1701790230; x=1702395030; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=OBeO4uD5WmpB1aJU//2ZqVMWJ1KMTm3aSrEbBbQl+GQ=; b=oLMD5nEf9t+LAxTDU3OYK+iloExtYxgA4KRp08bPiHC9XLrNuxJ2eu/cY9+I2RLgTG awrVkCcDvb3Pf69u2QP+T3fQDXVa6U/G/s7Kvn8Atn/huY/SiK6CWyW+yAwNxvFMRfJT wJztwAmafI+2jciFNNSqUX6yRRvt+Q3XiJtRkAJ1iY57BEH48ZKXFn8SAZo3VmyfxtNF ZqzeskgcTIPxXBo9YS62H+GsGiUHnA2Jy1hGfzTzsNUssCvH6k7cguosswhKQr1788mg Wmt6j7NsVwIRNUWF2LIIkO1TqWyaVMf6pwcM9KKuBFnkFAVmTFBm/JL+IKTCC8bkTlmU Rmhg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701790230; x=1702395030; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=OBeO4uD5WmpB1aJU//2ZqVMWJ1KMTm3aSrEbBbQl+GQ=; b=HyIdQLOJfXTsQ9LwyLVuleCCKI+tUBFWsQ3BbKeymKShC777U1oK7tKLQgdJXcs5vT mwJVF19L0qxoVjbvCQPaBNKGudRFhgEOysBgdDt5t19Fx7WmihrGydG700RHKGS8slLn GMwFN6mUqRav6+pYRqGyQs/HxNiJPjbDHdS3An4RI+qDbm1rQsJoxuGjneFrXlLjFIPG hEQHGl1JwwidMWgbsidGtR0Vs3MzLslDcQoLSBPDecSoauFsixhwgW/0bnbeHL19m7/e BJUaSUV0bhKVKqcBRbSbXfa09I3ksrMFhC4uXQKciImISfxmr8K+tDZ67dQNKMEIcJwa CU7A== X-Gm-Message-State: AOJu0YzJZmZcflUPQhikkkBNC6zpY+7G9XM1tYntDzBJ2dS1p1g9OuvM 7jNTvTOF+D4+gqC6CGyTuXWFbHBGTQgtOKSUAIs= X-Google-Smtp-Source: AGHT+IF9rv3X8VaxDOvqKs+349wzROnnmG726xgEil+piqg37VPmDRzOgvuzzu6IcYWKaE1tpgqzbw== X-Received: by 2002:a17:902:bd49:b0:1d0:b4cc:43ef with SMTP id b9-20020a170902bd4900b001d0b4cc43efmr2110852plx.24.1701790230489; Tue, 05 Dec 2023 07:30:30 -0800 (PST) Received: from rogue-one.tail33bf8.ts.net ([201.17.86.134]) by smtp.gmail.com with ESMTPSA id w3-20020a170902a70300b001cfc34965aesm10384427plq.50.2023.12.05.07.30.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Dec 2023 07:30:30 -0800 (PST) From: Pedro Tammela To: netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, marcelo.leitner@gmail.com, vladbu@nvidia.com, Pedro Tammela Subject: [PATCH net-next 1/2] net/sched: act_api: rely on rcu in tcf_idr_check_alloc Date: Tue, 5 Dec 2023 12:30:11 -0300 Message-Id: <20231205153012.484687-2-pctammela@mojatatu.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20231205153012.484687-1-pctammela@mojatatu.com> References: <20231205153012.484687-1-pctammela@mojatatu.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: kuba@kernel.org 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. Signed-off-by: Pedro Tammela --- net/sched/act_api.c | 56 +++++++++++++++++++++++++++------------------ 1 file changed, 34 insertions(+), 22 deletions(-) diff --git a/net/sched/act_api.c b/net/sched/act_api.c index abec5c45b5a4..79a044d2ae02 100644 --- a/net/sched/act_api.c +++ b/net/sched/act_api.c @@ -824,43 +824,55 @@ 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 -ENOENT; } + + 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); + return ret; } EXPORT_SYMBOL(tcf_idr_check_alloc);