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Goncalves" To: linux-rt-users , stable-rt , Steven Rostedt , Thomas Gleixner , Carsten Emde , Sebastian Andrzej Siewior , Daniel Wagner , Tom Zanussi , Clark Williams , Mark Gross , Jeff Brady , Wang Yong , Xuexin Jiang , Yang Yang , Xiaokai Ran , Jan Kiszka , Luis Goncalves Cc: Eric Dumazet , Pablo Neira Ayuso Subject: [PATCH RT 2/4] netfilter: nft_counter: Use u64_stats_t for statistic. Date: Tue, 25 Feb 2025 19:08:55 -0300 Message-ID: <20250225220857.216591-3-lgoncalv@redhat.com> In-Reply-To: <20250225220857.216591-1-lgoncalv@redhat.com> References: <20250225220857.216591-1-lgoncalv@redhat.com> Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 From: Sebastian Andrzej Siewior v5.10.234-rt127-rc1 stable review patch. If anyone has any objections, please let me know. ----------- [ Upstream commit 4a1d3acd6ea86075e77fcc1188c3fc372833ba73 ] The nft_counter uses two s64 counters for statistics. Those two are protected by a seqcount to ensure that the 64bit variable is always properly seen during updates even on 32bit architectures where the store is performed by two writes. A side effect is that the two counter (bytes and packet) are written and read together in the same window. This can be replaced with u64_stats_t. write_seqcount_begin()/ end() is replaced with u64_stats_update_begin()/ end() and behaves the same way as with seqcount_t on 32bit architectures. Additionally there is a preempt_disable on PREEMPT_RT to ensure that a reader does not preempt a writer. On 64bit architectures the macros are removed and the reads happen without any retries. This also means that the reader can observe one counter (bytes) from before the update and the other counter (packets) but that is okay since there is no requirement to have both counter from the same update window. Convert the statistic to u64_stats_t. There is one optimisation: nft_counter_do_init() and nft_counter_clone() allocate a new per-CPU counter and assign a value to it. During this assignment preemption is disabled which is not needed because the counter is not yet exposed to the system so there can not be another writer or reader. Therefore disabling preemption is omitted and raw_cpu_ptr() is used to obtain a pointer to a counter for the assignment. Cc: Eric Dumazet Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Pablo Neira Ayuso Signed-off-by: Jan Kiszka --- net/netfilter/nft_counter.c | 78 +++++++++++++++++++------------------ 1 file changed, 40 insertions(+), 38 deletions(-) diff --git a/net/netfilter/nft_counter.c b/net/netfilter/nft_counter.c index ea102b9a168b..79508b5f71d1 100644 --- a/net/netfilter/nft_counter.c +++ b/net/netfilter/nft_counter.c @@ -8,13 +8,18 @@ #include #include #include -#include +#include #include #include #include #include struct nft_counter { + u64_stats_t bytes; + u64_stats_t packets; +}; + +struct nft_counter_tot { s64 bytes; s64 packets; }; @@ -23,25 +28,24 @@ struct nft_counter_percpu_priv { struct nft_counter __percpu *counter; }; -static DEFINE_PER_CPU(seqcount_t, nft_counter_seq); +static DEFINE_PER_CPU(struct u64_stats_sync, nft_counter_sync); static inline void nft_counter_do_eval(struct nft_counter_percpu_priv *priv, struct nft_regs *regs, const struct nft_pktinfo *pkt) { + struct u64_stats_sync *nft_sync; struct nft_counter *this_cpu; - seqcount_t *myseq; local_bh_disable(); this_cpu = this_cpu_ptr(priv->counter); - myseq = this_cpu_ptr(&nft_counter_seq); - - write_seqcount_begin(myseq); + nft_sync = this_cpu_ptr(&nft_counter_sync); - this_cpu->bytes += pkt->skb->len; - this_cpu->packets++; + u64_stats_update_begin(nft_sync); + u64_stats_add(&this_cpu->bytes, pkt->skb->len); + u64_stats_inc(&this_cpu->packets); + u64_stats_update_end(nft_sync); - write_seqcount_end(myseq); local_bh_enable(); } @@ -64,17 +68,16 @@ static int nft_counter_do_init(const struct nlattr * const tb[], if (cpu_stats == NULL) return -ENOMEM; - preempt_disable(); - this_cpu = this_cpu_ptr(cpu_stats); + this_cpu = raw_cpu_ptr(cpu_stats); if (tb[NFTA_COUNTER_PACKETS]) { - this_cpu->packets = - be64_to_cpu(nla_get_be64(tb[NFTA_COUNTER_PACKETS])); + u64_stats_set(&this_cpu->packets, + be64_to_cpu(nla_get_be64(tb[NFTA_COUNTER_PACKETS]))); } if (tb[NFTA_COUNTER_BYTES]) { - this_cpu->bytes = - be64_to_cpu(nla_get_be64(tb[NFTA_COUNTER_BYTES])); + u64_stats_set(&this_cpu->bytes, + be64_to_cpu(nla_get_be64(tb[NFTA_COUNTER_BYTES]))); } - preempt_enable(); + priv->counter = cpu_stats; return 0; } @@ -102,40 +105,41 @@ static void nft_counter_obj_destroy(const struct nft_ctx *ctx, } static void nft_counter_reset(struct nft_counter_percpu_priv *priv, - struct nft_counter *total) + struct nft_counter_tot *total) { + struct u64_stats_sync *nft_sync; struct nft_counter *this_cpu; - seqcount_t *myseq; local_bh_disable(); this_cpu = this_cpu_ptr(priv->counter); - myseq = this_cpu_ptr(&nft_counter_seq); + nft_sync = this_cpu_ptr(&nft_counter_sync); + + u64_stats_update_begin(nft_sync); + u64_stats_add(&this_cpu->packets, -total->packets); + u64_stats_add(&this_cpu->bytes, -total->bytes); + u64_stats_update_end(nft_sync); - write_seqcount_begin(myseq); - this_cpu->packets -= total->packets; - this_cpu->bytes -= total->bytes; - write_seqcount_end(myseq); local_bh_enable(); } static void nft_counter_fetch(struct nft_counter_percpu_priv *priv, - struct nft_counter *total) + struct nft_counter_tot *total) { struct nft_counter *this_cpu; - const seqcount_t *myseq; u64 bytes, packets; unsigned int seq; int cpu; memset(total, 0, sizeof(*total)); for_each_possible_cpu(cpu) { - myseq = per_cpu_ptr(&nft_counter_seq, cpu); + struct u64_stats_sync *nft_sync = per_cpu_ptr(&nft_counter_sync, cpu); + this_cpu = per_cpu_ptr(priv->counter, cpu); do { - seq = read_seqcount_begin(myseq); - bytes = this_cpu->bytes; - packets = this_cpu->packets; - } while (read_seqcount_retry(myseq, seq)); + seq = u64_stats_fetch_begin(nft_sync); + bytes = u64_stats_read(&this_cpu->bytes); + packets = u64_stats_read(&this_cpu->packets); + } while (u64_stats_fetch_retry(nft_sync, seq)); total->bytes += bytes; total->packets += packets; @@ -146,7 +150,7 @@ static int nft_counter_do_dump(struct sk_buff *skb, struct nft_counter_percpu_priv *priv, bool reset) { - struct nft_counter total; + struct nft_counter_tot total; nft_counter_fetch(priv, &total); @@ -235,7 +239,7 @@ static int nft_counter_clone(struct nft_expr *dst, const struct nft_expr *src, g struct nft_counter_percpu_priv *priv_clone = nft_expr_priv(dst); struct nft_counter __percpu *cpu_stats; struct nft_counter *this_cpu; - struct nft_counter total; + struct nft_counter_tot total; nft_counter_fetch(priv, &total); @@ -243,11 +247,9 @@ static int nft_counter_clone(struct nft_expr *dst, const struct nft_expr *src, g if (cpu_stats == NULL) return -ENOMEM; - preempt_disable(); - this_cpu = this_cpu_ptr(cpu_stats); - this_cpu->packets = total.packets; - this_cpu->bytes = total.bytes; - preempt_enable(); + this_cpu = raw_cpu_ptr(cpu_stats); + u64_stats_set(&this_cpu->packets, total.packets); + u64_stats_set(&this_cpu->bytes, total.bytes); priv_clone->counter = cpu_stats; return 0; @@ -279,7 +281,7 @@ static int __init nft_counter_module_init(void) int cpu, err; for_each_possible_cpu(cpu) - seqcount_init(per_cpu_ptr(&nft_counter_seq, cpu)); + u64_stats_init(per_cpu_ptr(&nft_counter_sync, cpu)); err = nft_register_obj(&nft_counter_obj_type); if (err < 0)