From patchwork Sun Apr 9 17:39:22 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13206009 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B8E0C77B70 for ; Sun, 9 Apr 2023 17:39:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229485AbjDIRje (ORCPT ); Sun, 9 Apr 2023 13:39:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49420 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229552AbjDIRjd (ORCPT ); Sun, 9 Apr 2023 13:39:33 -0400 Received: from mail-wm1-x34a.google.com (mail-wm1-x34a.google.com [IPv6:2a00:1450:4864:20::34a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 817C235B0 for ; Sun, 9 Apr 2023 10:39:31 -0700 (PDT) Received: by mail-wm1-x34a.google.com with SMTP id l26-20020a05600c1d1a00b003edf85f6bb1so3010294wms.3 for ; Sun, 09 Apr 2023 10:39:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1681061970; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=De3yesDVMfZEEX8OSfiP+nxqpbJaFt7gWopDp+wvT80=; b=n2P08bz+Zn6zuZeJeAYcB9us2RwDjKLWuqq9olRcT/P4+HgdfbljjRcT8TEseuJfzJ dmrzskfn8CvJUFFs6bs3bpN7QT+8E0hncJo0qiOfvIOJkSYu99ez5+Tnhu46VTFJoREw VzrWW7DhQDq/tBhF2E32lI315MHLrZ/m/UhKa/D/vkmCWfwRfxFqNQ3wpBCmmhxDRXbK ib4tDwp75vWDQbmfLtmOxA57GdJ6PmnOUSzNCo0QNJJwENYnQlw3VkziCYnZoazff+Hg c6iGA7huQ0ne9zNe7X93cX/06ssdHQh5RRbdBAztwZGojrdIhprDgqJPcHD4qDJIG0nC zeoA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1681061970; 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=De3yesDVMfZEEX8OSfiP+nxqpbJaFt7gWopDp+wvT80=; b=2Ip//+oImOjssy+D/YmVzGprh6sED3jyPBFlWSe8vPjYgIku7fdxKAfeuWdme5awF+ q530pN+DAUnfezH8hkxXKt2yuqHNnES3MhMHmExpJWlXz3wg/k1Sb7++Es8jO57woMIi XhqcoJe5UMbWYlXU4sH/AfASTHJ0yU7iAIO+oJutMOi/5UG34TwgOrfPa2SwbSqpqrxz lEv+INEFuktf/k5t3gyaApQdoitKbAurmCTL3agB6G0uEvU8A4G87k+UDO44p1GhscD6 Zhan0L/vzxijGyr7vuuLHcxKGkEi2AaMCUIyOxVjUmhvRGoPnz7zheswC6u/Tp7dT4/z mBLw== X-Gm-Message-State: AAQBX9c3P36RYKt7+G4ssFv7wV1cZWPbeEji44WTOwjF1uPKPOjzY98L XItLyS4kNJDnud0Bg0kClgxOfb15SXZniMuT X-Google-Smtp-Source: AKy350YehyT3x+m7sJB1ykjffyiqkMQJHtEHpSQmmWnaKfsx6Nk5MvJAqQbL7y60ZkGcu8HuhsSwDbFO6cQHQdzY X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a7b:c7d4:0:b0:3ed:abb9:751e with SMTP id z20-20020a7bc7d4000000b003edabb9751emr1614435wmk.5.1681061970206; Sun, 09 Apr 2023 10:39:30 -0700 (PDT) Date: Sun, 9 Apr 2023 18:39:22 +0100 In-Reply-To: <20230409173923.1822455-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230409173923.1822455-1-vdonnefort@google.com> X-Mailer: git-send-email 2.40.0.577.gac1e443424-goog Message-ID: <20230409173923.1822455-2-vdonnefort@google.com> Subject: [PATCH v3 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 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org 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 */ 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 a page IDs list, 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. Signed-off-by: Vincent Donnefort diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 782e14f62201..5b3563507842 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 +213,9 @@ 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); #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..b89e0c8562b5 --- /dev/null +++ b/include/uapi/linux/trace_mmap.h @@ -0,0 +1,24 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_TRACE_MMAP_H_ +#define _UAPI_TRACE_MMAP_H_ + +#include + +#include + +struct ring_buffer_meta_header { +#if __BITS_PER_LONG == 64 + __u64 entries; + __u64 overrun; +#else + __u32 entries; + __u32 overrun; +#endif + __u32 pages_touched; + __u32 meta_page_size; + __u32 nr_data_pages; /* Number of pages in the ring-buffer */ + __u32 reader_page; /* Reader page ID, from 0 to nr_data_pages - 1 */ + __u32 read; /* Number of bytes read on the current reader page */ +}; + +#endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index af50d931b020..529702af7615 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -332,6 +332,7 @@ 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 +530,12 @@ struct ring_buffer_per_cpu { rb_time_t before_stamp; u64 event_stamp[MAX_NEST]; u64 read_stamp; + + int mapped; + struct mutex mapping_lock; + unsigned long *page_ids; /* ID to addr */ + struct ring_buffer_meta_header *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 */ @@ -1567,6 +1574,13 @@ static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer, /* Again, either we update tail_page or an interrupt does */ (void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page); } + + if (READ_ONCE(cpu_buffer->mapped)) { + /* Ensure the meta_page is ready */ + smp_rmb(); + WRITE_ONCE(cpu_buffer->meta_page->pages_touched, + local_read(&cpu_buffer->pages_touched)); + } } static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer, @@ -1735,6 +1749,7 @@ 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); + mutex_init(&cpu_buffer->mapping_lock); bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), GFP_KERNEL, cpu_to_node(cpu)); @@ -2173,7 +2188,6 @@ 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 @@ -2523,6 +2537,13 @@ rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer, local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes); local_inc(&cpu_buffer->pages_lost); + if (READ_ONCE(cpu_buffer->mapped)) { + /* Ensure the meta_page is ready */ + smp_rmb(); + WRITE_ONCE(cpu_buffer->meta_page->overrun, + local_read(&cpu_buffer->overrun)); + } + /* * The entries will be zeroed out when we move the * tail page. @@ -3179,6 +3200,14 @@ static inline void rb_event_discard(struct ring_buffer_event *event) static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer) { local_inc(&cpu_buffer->entries); + + if (READ_ONCE(cpu_buffer->mapped)) { + /* Ensure the meta_page is ready */ + smp_rmb(); + WRITE_ONCE(cpu_buffer->meta_page->entries, + local_read(&cpu_buffer->entries)); + } + rb_end_commit(cpu_buffer); } @@ -3482,7 +3511,7 @@ 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; @@ -4651,6 +4680,11 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->reader_page = reader; cpu_buffer->reader_page->read = 0; + if (cpu_buffer->mapped) { + WRITE_ONCE(cpu_buffer->meta_page->read, 0); + WRITE_ONCE(cpu_buffer->meta_page->reader_page, reader->id); + } + if (overwrite != cpu_buffer->last_overrun) { cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun; cpu_buffer->last_overrun = overwrite; @@ -4717,6 +4751,10 @@ static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer) length = rb_event_length(event); cpu_buffer->reader_page->read += length; + + if (cpu_buffer->mapped) + WRITE_ONCE(cpu_buffer->meta_page->read, + cpu_buffer->reader_page->read); } static void rb_advance_iter(struct ring_buffer_iter *iter) @@ -5285,6 +5323,13 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->lost_events = 0; cpu_buffer->last_overrun = 0; + if (cpu_buffer->mapped) { + WRITE_ONCE(cpu_buffer->meta_page->entries, 0); + WRITE_ONCE(cpu_buffer->meta_page->pages_touched, 0); + WRITE_ONCE(cpu_buffer->meta_page->overrun, 0); + WRITE_ONCE(cpu_buffer->meta_page->read, 0); + } + rb_head_page_activate(cpu_buffer); } @@ -5489,6 +5534,11 @@ 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 (READ_ONCE(cpu_buffer_a->mapped) || READ_ONCE(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; @@ -5722,7 +5772,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer, * Otherwise, we can simply swap the page with the one passed in. */ if (read || (len < (commit - read)) || - cpu_buffer->reader_page == cpu_buffer->commit_page) { + cpu_buffer->reader_page == cpu_buffer->commit_page || + cpu_buffer->mapped) { struct buffer_data_page *rpage = cpu_buffer->reader_page->page; unsigned int rpos = read; unsigned int pos = 0; @@ -5839,6 +5890,251 @@ int ring_buffer_read_page(struct trace_buffer *buffer, } EXPORT_SYMBOL_GPL(ring_buffer_read_page); +static void rb_free_page_ids(struct ring_buffer_per_cpu *cpu_buffer) +{ + int i; + + for (i = 0; i < cpu_buffer->nr_pages + 1; i++) + virt_to_page(cpu_buffer->page_ids[i])->mapping = NULL; + + 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; + + 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) +{ + unsigned long addr = (unsigned long)cpu_buffer->meta_page; + + virt_to_page(addr)->mapping = NULL; + free_page(addr); + cpu_buffer->meta_page = NULL; +} + +static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, + unsigned long *page_ids) +{ + struct ring_buffer_meta_header *meta = cpu_buffer->meta_page; + unsigned int nr_data_pages = cpu_buffer->nr_pages + 1; + struct buffer_page *first_page, *bpage; + int id = 0; + + page_ids[id] = (unsigned long)cpu_buffer->reader_page->page; + cpu_buffer->reader_page->id = id++; + + first_page = bpage = rb_set_head_page(cpu_buffer); + do { + if (id >= nr_data_pages) { + WARN_ON(1); + break; + } + + page_ids[id] = (unsigned long)bpage->page; + bpage->id = id; + + rb_inc_page(&bpage); + id++; + } while (bpage != first_page); + + /* install page ID to kern VA translation */ + cpu_buffer->page_ids = page_ids; + + meta->entries = 0; + meta->overrun = 0; + meta->pages_touched = 0; + meta->meta_page_size = PAGE_SIZE; + meta->nr_data_pages = nr_data_pages; + meta->reader_page = cpu_buffer->reader_page->id; + meta->read = cpu_buffer->reader_page->read; +} + +static inline 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]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (!cpu_buffer->mapped) { + mutex_unlock(&cpu_buffer->mapping_lock); + return ERR_PTR(-ENODEV); + } + + return cpu_buffer; +} + +static inline void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer) +{ + mutex_unlock(&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]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (cpu_buffer->mapped) { + WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped + 1); + 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 readers to block any page swap until the page IDs are + * assigned. + */ + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + + rb_setup_ids_meta_page(cpu_buffer, page_ids); + /* + * Ensure the writer will observe the meta-page before + * cpu_buffer->mapped. + */ + smp_wmb(); + WRITE_ONCE(cpu_buffer->mapped, 1); + + /* Init meta_page values unless the writer did it already */ + cmpxchg(&cpu_buffer->meta_page->entries, 0, + local_read(&cpu_buffer->entries)); + cmpxchg(&cpu_buffer->meta_page->overrun, 0, + local_read(&cpu_buffer->overrun)); + cmpxchg(&cpu_buffer->meta_page->pages_touched, 0, + local_read(&cpu_buffer->pages_touched)); + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); +unlock: + mutex_unlock(&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]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (!cpu_buffer->mapped) { + err = -ENODEV; + goto unlock; + } + + WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped - 1); + if (!cpu_buffer->mapped) { + /* Wait the writer and readers to observe !mapped */ + synchronize_rcu(); + + rb_free_page_ids(cpu_buffer); + rb_free_meta_page(cpu_buffer); + atomic_dec(&cpu_buffer->resize_disabled); + } + +unlock: + mutex_unlock(&cpu_buffer->mapping_lock); + + return err; +} + +/* + * +--------------+ + * | meta page | pgoff=0 + * +--------------+ + * | data page1 | page_ids=0 + * +--------------+ + * | data page2 | 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 = buffer->buffers[cpu]; + + if (!pgoff) + return virt_to_page((void *)cpu_buffer->meta_page); + + pgoff--; + if (pgoff > cpu_buffer->nr_pages) + return NULL; + + return virt_to_page(cpu_buffer->page_ids[pgoff]); +} + +int ring_buffer_get_reader_page(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long flags; + + 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); + if (!rb_per_cpu_empty(cpu_buffer)) { + unsigned int reader_size; + + WARN_ON(!rb_get_reader_page(cpu_buffer)); + + reader_size = rb_page_size(cpu_buffer->reader_page); + cpu_buffer->reader_page->read = reader_size; + cpu_buffer->meta_page->read = reader_size; + } + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + + 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 From patchwork Sun Apr 9 17:39:23 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13206010 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 52406C77B61 for ; Sun, 9 Apr 2023 17:39:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229622AbjDIRjm (ORCPT ); Sun, 9 Apr 2023 13:39:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229586AbjDIRje (ORCPT ); Sun, 9 Apr 2023 13:39:34 -0400 Received: from mail-ed1-x549.google.com (mail-ed1-x549.google.com [IPv6:2a00:1450:4864:20::549]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ACC8435BC for ; Sun, 9 Apr 2023 10:39:33 -0700 (PDT) Received: by mail-ed1-x549.google.com with SMTP id x1-20020a50ba81000000b0050234a3ad75so659929ede.23 for ; 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Sun, 09 Apr 2023 10:39:32 -0700 (PDT) Date: Sun, 9 Apr 2023 18:39:23 +0100 In-Reply-To: <20230409173923.1822455-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230409173923.1822455-1-vdonnefort@google.com> X-Mailer: git-send-email 2.40.0.577.gac1e443424-goog Message-ID: <20230409173923.1822455-3-vdonnefort@google.com> Subject: [PATCH v3 2/2] tracing: Allow user-space mapping of the ring-buffer 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 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org Currently, user-space extracts data from the ring-buffer via splice, which is handy for storage or network sharing. However, due to splice limitations, it is imposible to do real-time analysis without a copy. A solution for that problem is to let the user-space map the ring-buffer directly. The mapping exposed via the per-CPU file trace_pipe_raw. The first page is the meta-page and is followed by each page of the ring-buffer, ordered by their unique page ID. It is therefore easy to translate a page-ID to an offset in the mapping. * Meta-page -- include/uapi/linux/trace_mmap.h for a description * Page ID 0 * Page ID 1 ... The mapper must then do what use to be the kernel job: swap the reader with the head. This is done with a newly introduced ioctl: TRACE_MMAP_IOCTL_GET_READER_PAGE. Signed-off-by: Vincent Donnefort diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h index b89e0c8562b5..70b97c0ea888 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -21,4 +21,6 @@ struct ring_buffer_meta_header { __u32 read; /* Number of bytes read on the current reader page */ }; +#define TRACE_MMAP_IOCTL_GET_READER_PAGE _IO('T', 0x1) + #endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 45551c7b4c36..8a64ca87afaf 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6399,7 +6399,7 @@ static void tracing_set_nop(struct trace_array *tr) { if (tr->current_trace == &nop_trace) return; - + tr->current_trace->enabled--; if (tr->current_trace->reset) @@ -8432,15 +8432,21 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, return ret; } -/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { struct ftrace_buffer_info *info = file->private_data; struct trace_iterator *iter = &info->iter; - if (cmd) - return -ENOIOCTLCMD; + if (cmd == TRACE_MMAP_IOCTL_GET_READER_PAGE) + return ring_buffer_get_reader_page(iter->array_buffer->buffer, + iter->cpu_file); + else if (cmd) + return -ENOTTY; + /* + * An ioctl call with cmd 0 to the ring buffer file will wake up all + * waiters + */ mutex_lock(&trace_types_lock); iter->wait_index++; @@ -8453,6 +8459,63 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned return 0; } +static vm_fault_t tracing_buffers_mmap_fault(struct vm_fault *vmf) +{ + struct ftrace_buffer_info *info = vmf->vma->vm_file->private_data; + struct trace_iterator *iter = &info->iter; + vm_fault_t ret = VM_FAULT_SIGBUS; + struct page *page; + + page = ring_buffer_map_fault(iter->array_buffer->buffer, iter->cpu_file, + vmf->pgoff); + if (!page) + return ret; + + vmf->page = page; + + get_page(vmf->page); + vmf->page->mapping = vmf->vma->vm_file->f_mapping; + vmf->page->index = vmf->pgoff; + + return 0; +} + +static void tracing_buffers_mmap_close(struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info = vma->vm_file->private_data; + struct trace_iterator *iter = &info->iter; + + ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file); +} + +static void tracing_buffers_mmap_open(struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info = vma->vm_file->private_data; + struct trace_iterator *iter = &info->iter; + + WARN_ON(ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file)); +} + +static const struct vm_operations_struct tracing_buffers_vmops = { + .open = tracing_buffers_mmap_open, + .close = tracing_buffers_mmap_close, + .fault = tracing_buffers_mmap_fault, +}; + +static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info = filp->private_data; + struct trace_iterator *iter = &info->iter; + + if (vma->vm_flags & VM_WRITE) + return -EPERM; + + vm_flags_mod(vma, VM_DONTCOPY | VM_DONTDUMP, VM_MAYWRITE); + vma->vm_ops = &tracing_buffers_vmops; + + return ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file); +} + static const struct file_operations tracing_buffers_fops = { .open = tracing_buffers_open, .read = tracing_buffers_read, @@ -8461,6 +8524,7 @@ static const struct file_operations tracing_buffers_fops = { .splice_read = tracing_buffers_splice_read, .unlocked_ioctl = tracing_buffers_ioctl, .llseek = no_llseek, + .mmap = tracing_buffers_mmap, }; static ssize_t