From patchwork Wed Aug 16 04:59:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Hou Tao X-Patchwork-Id: 13354551 X-Patchwork-Delegate: bpf@iogearbox.net Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7852CC2D6; Wed, 16 Aug 2023 04:28:08 +0000 (UTC) Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D4BBF2112; Tue, 15 Aug 2023 21:28:05 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.30.67.169]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTP id 4RQZqz2ThMz4f3lK4; Wed, 16 Aug 2023 12:27:59 +0800 (CST) Received: from huaweicloud.com (unknown [10.175.124.27]) by APP4 (Coremail) with SMTP id gCh0CgD3hqlMUNxkOZhKAw--.35043S5; Wed, 16 Aug 2023 12:28:02 +0800 (CST) From: Hou Tao To: bpf@vger.kernel.org, netdev@vger.kernel.org, =?utf-8?q?Toke_H=C3=B8iland?= =?utf-8?q?-J=C3=B8rgensen?= Cc: "David S . Miller" , Jakub Kicinski , Jesper Dangaard Brouer , John Fastabend , =?utf-8?b?QmrDtnJuIFTDtnBlbA==?= , Martin KaFai Lau , Alexei Starovoitov , Andrii Nakryiko , Song Liu , Hao Luo , Yonghong Song , Daniel Borkmann , KP Singh , Stanislav Fomichev , Jiri Olsa , houtao1@huawei.com Subject: [PATCH bpf-next 1/2] bpf, cpumap: Use queue_rcu_work() to remove unnecessary rcu_barrier() Date: Wed, 16 Aug 2023 12:59:57 +0800 Message-Id: <20230816045959.358059-2-houtao@huaweicloud.com> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20230816045959.358059-1-houtao@huaweicloud.com> References: <20230816045959.358059-1-houtao@huaweicloud.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CM-TRANSID: gCh0CgD3hqlMUNxkOZhKAw--.35043S5 X-Coremail-Antispam: 1UD129KBjvJXoW3XryDuw4fJw47ZF1DCr45Jrb_yoW3Xr1kpF Wftw17Gr48Xw4v93y8Xw18Ar1Yvrs3Wa4UG340k34rA3ZxJrZxXFW0kFyIyFy5urWkur17 CFsFqFWkGayDAaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUBjb4IE77IF4wAFF20E14v26rWj6s0DM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28IrcIa0xkI8VA2jI8067AKxVWUGw A2048vs2IY020Ec7CjxVAFwI0_Gr0_Xr1l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxS w2x7M28EF7xvwVC0I7IYx2IY67AKxVW7JVWDJwA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxV WxJVW8Jr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_ GcCE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx 0E2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWU JVW8JwACjcxG0xvY0x0EwIxGrwACI402YVCY1x02628vn2kIc2xKxwCF04k20xvY0x0EwI xGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E7480 Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_GFv_WrylIxkGc2Ij64vIr41lIxAIcVC0I7 IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_Gr0_Cr1lIxAIcVCF04k2 6cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2jsIEc7CjxV AFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x07jn9N3UUUUU= X-CM-SenderInfo: xkrx3t3r6k3tpzhluzxrxghudrp/ X-CFilter-Loop: Reflected X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,SPF_HELO_NONE, SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net X-Patchwork-Delegate: bpf@iogearbox.net From: Hou Tao As for now __cpu_map_entry_replace() uses call_rcu() to wait for the inflight xdp program to exit the RCU read critical section, and then launch kworker cpu_map_kthread_stop() to call kthread_stop() to flush all pending xdp frames or skbs. But it is unnecessary to use rcu_barrier() in cpu_map_kthread_stop() to wait for the completion of __cpu_map_entry_free(), because rcu_barrier() will wait for all pending RCU callbacks and cpu_map_kthread_stop() only needs to wait for the completion of a specific __cpu_map_entry_free(). So use queue_rcu_work() to replace call_rcu(), schedule_work() and rcu_barrier(). queue_rcu_work() will queue a __cpu_map_entry_free() kworker after a RCU grace period. Because __cpu_map_entry_free() is running in a kworker context, so it is OK to do all of these freeing procedures include kthread_stop() in it. After the update, there is no need to do reference-counting for bpf_cpu_map_entry, because bpf_cpu_map_entry is freed directly in __cpu_map_entry_free(), so just remove it. Signed-off-by: Hou Tao Reviewed-by: Toke Høiland-Jørgensen --- kernel/bpf/cpumap.c | 96 +++++++++++++-------------------------------- 1 file changed, 27 insertions(+), 69 deletions(-) diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c index ef28c64f1eb1..93fbd3e5079e 100644 --- a/kernel/bpf/cpumap.c +++ b/kernel/bpf/cpumap.c @@ -68,11 +68,8 @@ struct bpf_cpu_map_entry { struct bpf_cpumap_val value; struct bpf_prog *prog; - atomic_t refcnt; /* Control when this struct can be free'ed */ - struct rcu_head rcu; - - struct work_struct kthread_stop_wq; struct completion kthread_running; + struct rcu_work free_work; }; struct bpf_cpu_map { @@ -117,11 +114,6 @@ static struct bpf_map *cpu_map_alloc(union bpf_attr *attr) return &cmap->map; } -static void get_cpu_map_entry(struct bpf_cpu_map_entry *rcpu) -{ - atomic_inc(&rcpu->refcnt); -} - static void __cpu_map_ring_cleanup(struct ptr_ring *ring) { /* The tear-down procedure should have made sure that queue is @@ -142,35 +134,6 @@ static void __cpu_map_ring_cleanup(struct ptr_ring *ring) } } -static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu) -{ - if (atomic_dec_and_test(&rcpu->refcnt)) { - if (rcpu->prog) - bpf_prog_put(rcpu->prog); - /* The queue should be empty at this point */ - __cpu_map_ring_cleanup(rcpu->queue); - ptr_ring_cleanup(rcpu->queue, NULL); - kfree(rcpu->queue); - kfree(rcpu); - } -} - -/* called from workqueue, to workaround syscall using preempt_disable */ -static void cpu_map_kthread_stop(struct work_struct *work) -{ - struct bpf_cpu_map_entry *rcpu; - - rcpu = container_of(work, struct bpf_cpu_map_entry, kthread_stop_wq); - - /* Wait for flush in __cpu_map_entry_free(), via full RCU barrier, - * as it waits until all in-flight call_rcu() callbacks complete. - */ - rcu_barrier(); - - /* kthread_stop will wake_up_process and wait for it to complete */ - kthread_stop(rcpu->kthread); -} - static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu, struct list_head *listp, struct xdp_cpumap_stats *stats) @@ -395,7 +358,6 @@ static int cpu_map_kthread_run(void *data) } __set_current_state(TASK_RUNNING); - put_cpu_map_entry(rcpu); return 0; } @@ -472,9 +434,6 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value, if (IS_ERR(rcpu->kthread)) goto free_prog; - get_cpu_map_entry(rcpu); /* 1-refcnt for being in cmap->cpu_map[] */ - get_cpu_map_entry(rcpu); /* 1-refcnt for kthread */ - /* Make sure kthread runs on a single CPU */ kthread_bind(rcpu->kthread, cpu); wake_up_process(rcpu->kthread); @@ -501,40 +460,40 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value, return NULL; } -static void __cpu_map_entry_free(struct rcu_head *rcu) +static void __cpu_map_entry_free(struct work_struct *work) { struct bpf_cpu_map_entry *rcpu; /* This cpu_map_entry have been disconnected from map and one - * RCU grace-period have elapsed. Thus, XDP cannot queue any + * RCU grace-period have elapsed. Thus, XDP cannot queue any * new packets and cannot change/set flush_needed that can * find this entry. */ - rcpu = container_of(rcu, struct bpf_cpu_map_entry, rcu); + rcpu = container_of(to_rcu_work(work), struct bpf_cpu_map_entry, free_work); + + /* kthread_stop will wake_up_process and wait for it to complete. + * cpu_map_kthread_run() makes sure the pointer ring is empty + * before exiting. + */ + kthread_stop(rcpu->kthread); + if (rcpu->prog) + bpf_prog_put(rcpu->prog); + /* The queue should be empty at this point */ + __cpu_map_ring_cleanup(rcpu->queue); + ptr_ring_cleanup(rcpu->queue, NULL); + kfree(rcpu->queue); free_percpu(rcpu->bulkq); - /* Cannot kthread_stop() here, last put free rcpu resources */ - put_cpu_map_entry(rcpu); + kfree(rcpu); } -/* After xchg pointer to bpf_cpu_map_entry, use the call_rcu() to - * ensure any driver rcu critical sections have completed, but this - * does not guarantee a flush has happened yet. Because driver side - * rcu_read_lock/unlock only protects the running XDP program. The - * atomic xchg and NULL-ptr check in __cpu_map_flush() makes sure a - * pending flush op doesn't fail. - * - * The bpf_cpu_map_entry is still used by the kthread, and there can - * still be pending packets (in queue and percpu bulkq). A refcnt - * makes sure to last user (kthread_stop vs. call_rcu) free memory - * resources. - * - * The rcu callback __cpu_map_entry_free flush remaining packets in - * percpu bulkq to queue. Due to caller map_delete_elem() disable - * preemption, cannot call kthread_stop() to make sure queue is empty. - * Instead a work_queue is started for stopping kthread, - * cpu_map_kthread_stop, which waits for an RCU grace period before - * stopping kthread, emptying the queue. +/* After the xchg of the bpf_cpu_map_entry pointer, we need to make sure the old + * entry is no longer in use before freeing. We use queue_rcu_work() to call + * __cpu_map_entry_free() in a separate workqueue after waiting for an RCU grace + * period. This means that (a) all pending enqueue and flush operations have + * completed (because of the RCU callback), and (b) we are in a workqueue + * context where we can stop the kthread and wait for it to exit before freeing + * everything. */ static void __cpu_map_entry_replace(struct bpf_cpu_map *cmap, u32 key_cpu, struct bpf_cpu_map_entry *rcpu) @@ -543,9 +502,8 @@ static void __cpu_map_entry_replace(struct bpf_cpu_map *cmap, old_rcpu = unrcu_pointer(xchg(&cmap->cpu_map[key_cpu], RCU_INITIALIZER(rcpu))); if (old_rcpu) { - call_rcu(&old_rcpu->rcu, __cpu_map_entry_free); - INIT_WORK(&old_rcpu->kthread_stop_wq, cpu_map_kthread_stop); - schedule_work(&old_rcpu->kthread_stop_wq); + INIT_RCU_WORK(&old_rcpu->free_work, __cpu_map_entry_free); + queue_rcu_work(system_wq, &old_rcpu->free_work); } } @@ -557,7 +515,7 @@ static long cpu_map_delete_elem(struct bpf_map *map, void *key) if (key_cpu >= map->max_entries) return -EINVAL; - /* notice caller map_delete_elem() use preempt_disable() */ + /* notice caller map_delete_elem() uses rcu_read_lock() */ __cpu_map_entry_replace(cmap, key_cpu, NULL); return 0; }