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[2620:137:e000::1:20]) by mx.google.com with ESMTP id r29-20020a638f5d000000b004fb97a4c534si1455047pgn.875.2023.02.12.07.41.38; Sun, 12 Feb 2023 07:42:09 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20210112 header.b=SWZkvnVM; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229707AbjBLPdN (ORCPT + 99 others); Sun, 12 Feb 2023 10:33:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36116 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229581AbjBLPdL (ORCPT ); Sun, 12 Feb 2023 10:33:11 -0500 Received: from mail-wm1-x349.google.com (mail-wm1-x349.google.com [IPv6:2a00:1450:4864:20::349]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 018FCC167 for ; Sun, 12 Feb 2023 07:33:08 -0800 (PST) Received: by mail-wm1-x349.google.com with SMTP id ay19-20020a05600c1e1300b003dc54daba42so5008217wmb.7 for ; Sun, 12 Feb 2023 07:33:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=xnvuwkJ3TaNv9//GI4G63WEbKVVNVqAtuFtA55HGiRo=; b=SWZkvnVMVjChjhq/70PwpGiaAPT56FVJaS8DfOojNVdAxP4+oQb/goqTI7HNMfiS9H H+qOwCQh9TkbRrm8/EGTDY0MyKObpeg9/CwJ+vrRm0rqFgwBddVQPLkBY586Mob3P9rx BFiToAHjG6DdXa07Xaa17vpOGjGrFvt7WoFEg4O+vtl2ZdQ15lm66qxe3qts4TaPsVGQ 8mvZ79ONLG7NbxMQLiB1RmtuFoJfbcwvjSldEiahgXxU8TuV5k3hwlOj6ekOLfpqGIDg vm5qfnADR5tQuj8An2bodsC1eNEqOFSmVtLcu+6rWiU9q1GlU9Vq74f1kzW8G6gXkT/c Uq0Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=xnvuwkJ3TaNv9//GI4G63WEbKVVNVqAtuFtA55HGiRo=; b=dPzwTqmMwgl/mImxU2XaYAeTjbDmltZ78aqy18zUxP0Cg7ONXLL8mTijNRxJNGmVm3 MLOOomQdWO1TJncT7qKlT7WSWj8t4ZJ2D4pAIZk8VNRy86xVX0bUT9Cc/Rj+B65lEj6S sKszs58PCGlesPBvYhabVEwrEst8rfg+Qs9cTHyr3fl5qq+L6jwSP7X4wuPOAn3g9fw4 7pDYo2rVvDEkwqeJfKkk4PUKuVrJbMyi4j3VAJxCV1pS2kdXsD9XLNp2J3PtqUJuJRox pFEIIv4LlLj9wsOW5XsVefHrkjSq0coHO6EvuhQkOBmwy8yn8pX4HRi7AvLu5JjxVOSO c4rQ== X-Gm-Message-State: AO0yUKWz8v48XK0tQ12k4K9A+Djq8m9ZWMJQopJ3qPhh5snbBYApsPjU ty+1AYZ/x12qHBj8QnbfT+ECTAMbyJRn5IeV X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a05:600c:45c9:b0:3e1:336:d219 with SMTP id s9-20020a05600c45c900b003e10336d219mr730294wmo.145.1676215986690; Sun, 12 Feb 2023 07:33:06 -0800 (PST) Date: Sun, 12 Feb 2023 15:32:49 +0000 In-Reply-To: <20230212153250.1099136-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230212153250.1099136-1-vdonnefort@google.com> X-Mailer: git-send-email 2.39.1.581.gbfd45094c4-goog Message-ID: <20230212153250.1099136-2-vdonnefort@google.com> Subject: [RFC PATCH 1/2] ring-buffer: Introducing ring-buffer mapping functions From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: kernel-team@android.com, Vincent Donnefort X-Spam-Status: No, score=-9.6 required=5.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1757640423554652151?= X-GMAIL-MSGID: =?utf-8?q?1757640423554652151?= In preparation for allowing the user-space to map a ring-buffer, add a set of mapping functions: ring_buffer_{map,unmap}() ring_buffer_map_fault() And controls on the ring-buffer: ring_buffer_get_reader_page() /* swap reader and head */ ring_buffer_update_meta_page() Mapping the ring-buffer also involves: A unique ID for each page of the ring-buffer, as currently the pages are only identified through their in-kernel VA. A meta-page, where are stored statistics about the ring-buffer and the list of pages ID, ordered. A field gives what page is the reader one and one to gives where the ring-buffer starts in the list of data pages. The linear mapping exposes the meta-page, and each page of the ring-buffer, ordered following their unique ID, assigned during the first mapping. Once mapped, no page can get in or out of the ring-buffer: the buffer size will remain unmodified and the splice enabling functions will in reality simply memcpy the data instead of swapping pages. Also, the meta-page being... a single page, this limits at the moment the number of pages in the ring-buffer that can be mapped. Signed-off-by: Vincent Donnefort diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 782e14f62201..4897e17ebdde 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -6,6 +6,8 @@ #include #include +#include + struct trace_buffer; struct ring_buffer_iter; @@ -211,4 +213,10 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node); #define trace_rb_cpu_prepare NULL #endif +int ring_buffer_map(struct trace_buffer *buffer, int cpu); +int ring_buffer_unmap(struct trace_buffer *buffer, int cpu); +struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu, + unsigned long pgoff); +int ring_buffer_get_reader_page(struct trace_buffer *buffer, int cpu); +int ring_buffer_update_meta_page(struct trace_buffer *buffer, int cpu); #endif /* _LINUX_RING_BUFFER_H */ diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h new file mode 100644 index 000000000000..0f3282fa1a94 --- /dev/null +++ b/include/uapi/linux/trace_mmap.h @@ -0,0 +1,14 @@ +#ifndef _UAPI_TRACE_MMAP_H_ +#define _UAPI_TRACE_MMAP_H_ + +struct ring_buffer_meta_page { + __u64 entries; + __u64 overrun; + __u32 pages_touched; + __u32 reader_page; + __u32 nr_data_pages; + __u32 data_page_head; + __u32 data_pages[]; +}; + +#endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index c366a0a9ddba..ffbb216a18a9 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -20,6 +20,7 @@ #include #include #include +#include #include #include #include @@ -332,6 +333,7 @@ struct buffer_page { local_t entries; /* entries on this page */ unsigned long real_end; /* real end of data */ struct buffer_data_page *page; /* Actual data page */ + u32 id; /* ID for external mapping */ }; /* @@ -529,6 +531,12 @@ struct ring_buffer_per_cpu { rb_time_t before_stamp; u64 event_stamp[MAX_NEST]; u64 read_stamp; + + atomic_t mapped; + struct rw_semaphore mapping_lock; + unsigned long *page_ids; /* ID to addr */ + void *meta_page; + /* ring buffer pages to update, > 0 to add, < 0 to remove */ long nr_pages_to_update; struct list_head new_pages; /* new pages to add */ @@ -1452,12 +1460,41 @@ static inline void rb_inc_page(struct buffer_page **bpage) *bpage = list_entry(p, struct buffer_page, list); } +static inline void +rb_meta_page_head_move(struct ring_buffer_per_cpu *cpu_buffer, unsigned long num) +{ + struct ring_buffer_meta_page *meta = cpu_buffer->meta_page; + unsigned long head_id = meta->data_page_head; + + /* No bookkeeping necessary */ + if (!atomic_read(&cpu_buffer->mapped)) + return; + + meta->data_page_head = (head_id + num) % cpu_buffer->nr_pages; +} + +static inline void +rb_meta_page_head_swap(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct ring_buffer_meta_page *meta = cpu_buffer->meta_page; + + /* No bookkeeping necessary */ + if (!atomic_read(&cpu_buffer->mapped)) + return; + + meta->reader_page = cpu_buffer->reader_page->id; + meta->data_pages[meta->data_page_head] = cpu_buffer->head_page->id; + + rb_meta_page_head_move(cpu_buffer, 1); +} + static struct buffer_page * rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer) { struct buffer_page *head; struct buffer_page *page; struct list_head *list; + unsigned long cnt = 0; int i; if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page)) @@ -1479,9 +1516,11 @@ rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer) do { if (rb_is_head_page(page, page->list.prev)) { cpu_buffer->head_page = page; + rb_meta_page_head_move(cpu_buffer, cnt); return page; } rb_inc_page(&page); + cnt++; } while (page != head); } @@ -1757,6 +1796,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu) init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters); init_waitqueue_head(&cpu_buffer->irq_work.waiters); init_waitqueue_head(&cpu_buffer->irq_work.full_waiters); + init_rwsem(&cpu_buffer->mapping_lock); bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), GFP_KERNEL, cpu_to_node(cpu)); @@ -2195,7 +2235,6 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size, /* prevent another thread from changing buffer sizes */ mutex_lock(&buffer->mutex); - if (cpu_id == RING_BUFFER_ALL_CPUS) { /* * Don't succeed if resizing is disabled, as a reader might be @@ -3504,7 +3543,7 @@ static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer, return; /* - * If this interrupted another event, + * If this interrupted another event, */ if (atomic_inc_return(this_cpu_ptr(&checking)) != 1) goto out; @@ -4665,6 +4704,7 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) * Now make the new head point back to the reader page. */ rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list; + rb_meta_page_head_swap(cpu_buffer); rb_inc_page(&cpu_buffer->head_page); local_inc(&cpu_buffer->pages_read); @@ -5511,6 +5551,12 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, cpu_buffer_a = buffer_a->buffers[cpu]; cpu_buffer_b = buffer_b->buffers[cpu]; + if (atomic_read(&cpu_buffer_a->mapped) || + atomic_read(&cpu_buffer_b->mapped)) { + ret = -EBUSY; + goto out; + } + /* At least make sure the two buffers are somewhat the same */ if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages) goto out; @@ -5804,14 +5850,19 @@ int ring_buffer_read_page(struct trace_buffer *buffer, cpu_buffer->read += rb_page_entries(reader); cpu_buffer->read_bytes += BUF_PAGE_SIZE; - /* swap the pages */ - rb_init_page(bpage); - bpage = reader->page; - reader->page = *data_page; - local_set(&reader->write, 0); - local_set(&reader->entries, 0); - reader->read = 0; - *data_page = bpage; + if (likely(!atomic_read(&cpu_buffer->mapped))) { + /* swap the pages */ + rb_init_page(bpage); + bpage = reader->page; + reader->page = *data_page; + local_set(&reader->write, 0); + local_set(&reader->entries, 0); + reader->read = 0; + *data_page = bpage; + } else { + memcpy(bpage->data, cpu_buffer->reader_page->page->data, + PAGE_SIZE); + } /* * Use the real_end for the data size, @@ -5856,6 +5907,290 @@ int ring_buffer_read_page(struct trace_buffer *buffer, } EXPORT_SYMBOL_GPL(ring_buffer_read_page); +#define META_PAGE_MAX_PAGES \ + ((PAGE_SIZE - (offsetof(struct ring_buffer_meta_page, data_page_head))) >> 2) + +static void rb_free_page_ids(struct ring_buffer_per_cpu *cpu_buffer) +{ + kfree(cpu_buffer->page_ids); + cpu_buffer->page_ids = NULL; +} + +static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + if (cpu_buffer->meta_page) + return 0; + + if ((cpu_buffer->nr_pages + 1) > META_PAGE_MAX_PAGES) + return -E2BIG; + + cpu_buffer->meta_page = page_to_virt(alloc_page(GFP_USER)); + if (!cpu_buffer->meta_page) + return -ENOMEM; + + return 0; +} + +static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + free_page((unsigned long)cpu_buffer->meta_page); + cpu_buffer->meta_page = NULL; +} + +static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct ring_buffer_meta_page *meta; + unsigned long flags; + + /* Update the head page if the writer moved it */ + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + rb_set_head_page(cpu_buffer); + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + + /* + * Instead of letting the writer carry the meta page burden, + * give the responsibility to the reader. + */ + meta = (struct ring_buffer_meta_page *)cpu_buffer->meta_page; + meta->entries = local_read(&cpu_buffer->entries); + meta->pages_touched = local_read(&cpu_buffer->pages_touched); + meta->overrun = local_read(&cpu_buffer->overrun); +} + +static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, + unsigned long *page_ids) +{ + struct buffer_page *first_page, *bpage; + struct ring_buffer_meta_page *meta; + int id = 0, i = 0; + + meta = (struct ring_buffer_meta_page *)cpu_buffer->meta_page; + + meta->reader_page = cpu_buffer->reader_page->id; + meta->nr_data_pages = cpu_buffer->nr_pages; + meta->data_page_head = 0; + + page_ids[id] = (unsigned long)cpu_buffer->reader_page->page; + cpu_buffer->reader_page->id = id; + + id++; + + first_page = bpage = rb_set_head_page(cpu_buffer); + do { + if (i >= META_PAGE_MAX_PAGES) { + WARN_ON(1); + break; + } + + page_ids[id] = (unsigned long)bpage->page; + bpage->id = id; + meta->data_pages[i] = id; + + rb_inc_page(&bpage); + i++; id++; + } while (bpage != first_page); + + /* install page ID to kern VA translation */ + cpu_buffer->page_ids = page_ids; +} + +static struct ring_buffer_per_cpu * +rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return ERR_PTR(-EINVAL); + + cpu_buffer = buffer->buffers[cpu]; + + down_read(&cpu_buffer->mapping_lock); + + if (!atomic_read(&cpu_buffer->mapped)) { + up_read(&cpu_buffer->mapping_lock); + return ERR_PTR(-ENODEV); + } + + return cpu_buffer; +} + +void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer) +{ + up_read(&cpu_buffer->mapping_lock); +} + +int ring_buffer_map(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long flags, *page_ids; + int err = 0; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer = buffer->buffers[cpu]; + + down_write(&cpu_buffer->mapping_lock); + + if (atomic_read(&cpu_buffer->mapped)) { + atomic_inc(&cpu_buffer->mapped); + goto unlock; + } + + /* prevent another thread from changing buffer sizes */ + mutex_lock(&buffer->mutex); + atomic_inc(&cpu_buffer->resize_disabled); + mutex_unlock(&buffer->mutex); + + err = rb_alloc_meta_page(cpu_buffer); + if (err) { + atomic_dec(&cpu_buffer->resize_disabled); + goto unlock; + } + + /* page_ids include the reader page while nr_pages does not */ + page_ids = kzalloc(sizeof(*page_ids) * (cpu_buffer->nr_pages + 1), + GFP_KERNEL); + if (!page_ids) { + rb_free_meta_page(cpu_buffer); + atomic_dec(&cpu_buffer->resize_disabled); + err = -ENOMEM; + goto unlock; + } + + /* + * Lock all other readers as we'll disable the splice and enable the + * meta-page data_head_page book keeping. + */ + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + + rb_setup_ids_meta_page(cpu_buffer, page_ids); + atomic_inc(&cpu_buffer->mapped); + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); +unlock: + up_write(&cpu_buffer->mapping_lock); + + return err; +} + +int ring_buffer_unmap(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + int err = 0; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer = buffer->buffers[cpu]; + + down_write(&cpu_buffer->mapping_lock); + + if (!atomic_read(&cpu_buffer->mapped)) { + err = -ENODEV; + goto unlock; + } + + if (atomic_dec_and_test(&cpu_buffer->mapped)) { + unsigned long flags; + + /* + * Lock all readers to make sure none will attempt meta-page + * book keeping while we free the resources + */ + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + + rb_free_page_ids(cpu_buffer); + rb_free_meta_page(cpu_buffer); + atomic_dec(&cpu_buffer->resize_disabled); + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + } + +unlock: + up_write(&cpu_buffer->mapping_lock); + + return err; +} + +/* + * +--------------+ + * | meta page | pgoff=0 + * +--------------+ + * | data page1 | pgoff=1 page_ids=0 + * +--------------+ + * | data page2 | pgoff=2 page_ids=1 + * ... + */ +struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu, + unsigned long pgoff) +{ + struct ring_buffer_per_cpu *cpu_buffer; + struct page *page = NULL; + + cpu_buffer = rb_get_mapped_buffer(buffer, cpu); + if (IS_ERR(cpu_buffer)) + return NULL; + + if (!cpu_buffer->page_ids) { + WARN_ON(1); + goto put; + } + + if (pgoff == 0) { + page = virt_to_page(cpu_buffer->meta_page); + } else { + pgoff--; + + if (pgoff > (cpu_buffer->nr_pages)) + goto put; + + page = virt_to_page(cpu_buffer->page_ids[pgoff]); + } +put: + rb_put_mapped_buffer(cpu_buffer); + + return page; +} + +int ring_buffer_get_reader_page(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + struct buffer_page *bpage, *reader; + unsigned long flags; + int err = 0; + + cpu_buffer = rb_get_mapped_buffer(buffer, cpu); + if (IS_ERR(cpu_buffer)) + return (int)PTR_ERR(cpu_buffer); + + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + reader = cpu_buffer->reader_page; + reader->read = rb_page_size(reader); + bpage = rb_get_reader_page(cpu_buffer); + if (!bpage) + err = -ENODEV; + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + + rb_put_mapped_buffer(cpu_buffer); + + return err; +} + +int ring_buffer_update_meta_page(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + + cpu_buffer = rb_get_mapped_buffer(buffer, cpu); + if (IS_ERR(cpu_buffer)) + return PTR_ERR(cpu_buffer); + + rb_update_meta_page(cpu_buffer); + rb_put_mapped_buffer(cpu_buffer); + + return 0; +} + /* * We only allocate new buffers, never free them if the CPU goes down. * If we were to free the buffer, then the user would lose any trace that was in