From nobody Thu Dec 25 21:48:33 2025 Received: from mail-wm1-f73.google.com (mail-wm1-f73.google.com [209.85.128.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0E484524CE for ; Thu, 11 Jan 2024 16:17:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="W2MEm62t" Received: by mail-wm1-f73.google.com with SMTP id 5b1f17b1804b1-40e46bceed8so36387275e9.0 for ; Thu, 11 Jan 2024 08:17:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1704989844; x=1705594644; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=tDSYk7XYW6OJAyFvY7TTHo+xr/O1Sc5t/M2lwwtKZ4I=; b=W2MEm62tY4oCFHtvsWJG2vhUIpagMYTO6SiB7O8eUyS9t079Mb5J1ilhTYQIKzWm8o 3FLNNkLxkLr6iNlLk5dnARceN9ngz+xISe64GAUCcCWtMhz8ZFKT+kZhs1wbEzxchqGZ MfxNdqWckoRsHngZGA4bmU2uXYb9XZ6Ud9wMMo64hT0CjCDYXoUi7Yr0GpGKpPRfl+8g Au+wgSwpRD0I+pqlNyaE/j3mm45PHVM8unB4uFHibxrf/DO1SNgI2SPlt7MiD/iMTtfM Z61Pl6WUwYTElUv8rE28VujfzMAmEHnAnYym/iPwsQlkn89cFKIO3nhg2JtK6qzUI8cO 7YxA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704989844; x=1705594644; 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=tDSYk7XYW6OJAyFvY7TTHo+xr/O1Sc5t/M2lwwtKZ4I=; b=Y9Z8RtsZjZVRfMH6P7gunjOHM3sqZmf9bd465gaDpd0a2E/TDq+qR/7PfHqyzF7xit shAUA0qzCYLkNIay9eABH0rEoNdVydOVNQ33P02+4NFJg/ZAkSCTkdW/FdJS9GNxL1um xNqXQqP+/qITrHAnRjTO5RrjaJww1AeABqwJ1+zZlFoxjlq1qzS3tDocjxx0bVF9PdvL GTeIrk9P701M1rBEP+lbWXeko70q/5iNLTm6kQFHqinL3uoW8WZB+dzAF+xUFACpXVpm XP+s4XvqDT+JL1razAGwPspzVAsUz+UIGmTGbJtGAdrZhPF2pF6XwRNXOM316X4BoqnS Nipw== X-Gm-Message-State: AOJu0Yx23e0IBM/0lgdOfHLUKNB10UaG/z/QGGq5b+aC5PMcUtO7chRo N0qz17si5J23znnpaU0GNLKlDDZc9q1jrzhSG2Lp8ks= X-Google-Smtp-Source: AGHT+IG988fV+y4v6eRMN4Qtm6s3lp6PVXdREEpYx8NOLeZVatTVFpsgszJvTsrdmt0s0u6BLPj8NZ9YrZBeedCU X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a05:600c:1c88:b0:40e:48b2:b337 with SMTP id k8-20020a05600c1c8800b0040e48b2b337mr147wms.5.1704989844417; Thu, 11 Jan 2024 08:17:24 -0800 (PST) Date: Thu, 11 Jan 2024 16:17:09 +0000 In-Reply-To: <20240111161712.1480333-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240111161712.1480333-1-vdonnefort@google.com> X-Mailer: git-send-email 2.43.0.275.g3460e3d667-goog Message-ID: <20240111161712.1480333-3-vdonnefort@google.com> Subject: [PATCH v11 2/5] 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: mathieu.desnoyers@efficios.com, kernel-team@android.com, Vincent Donnefort Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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_map_get_reader() /* swap reader and head */ Mapping the ring-buffer also involves: A unique ID for each subbuf of the ring-buffer, currently they are only identified through their in-kernel VA. A meta-page, where are stored ring-buffer statistics and a description for the current reader The linear mapping exposes the meta-page, and each subbuf of the ring-buffer, ordered following their unique ID, assigned during the first mapping. Once mapped, no subbuf 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 subbufs. Signed-off-by: Vincent Donnefort diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index fa802db216f9..0841ba8bab14 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -6,6 +6,8 @@ #include #include =20 +#include + struct trace_buffer; struct ring_buffer_iter; =20 @@ -221,4 +223,9 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist= _node *node); #define trace_rb_cpu_prepare NULL #endif =20 +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_map_get_reader(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_mma= p.h new file mode 100644 index 000000000000..bde39a73ce65 --- /dev/null +++ b/include/uapi/linux/trace_mmap.h @@ -0,0 +1,45 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _TRACE_MMAP_H_ +#define _TRACE_MMAP_H_ + +#include + +/** + * struct trace_buffer_meta - Ring-buffer Meta-page description + * @entries: Number of entries in the ring-buffer. + * @overrun: Number of entries lost in the ring-buffer. + * @read: Number of entries that have been read. + * @subbufs_touched: Number of subbufs that have been filled. + * @subbufs_lost: Number of subbufs lost to overrun. + * @subbufs_read: Number of subbufs that have been read. + * @reader.lost_events: Number of events lost at the time of the reader sw= ap. + * @reader.id: subbuf ID of the current reader. From 0 to @nr_subbufs - 1 + * @reader.read: Number of bytes read on the reader subbuf. + * @subbuf_size: Size of each subbuf, including the header. + * @nr_subbufs: Number of subbfs in the ring-buffer. + * @meta_page_size: Size of this meta-page. + * @meta_struct_len: Size of this structure. + */ +struct trace_buffer_meta { + unsigned long entries; + unsigned long overrun; + unsigned long read; + + unsigned long subbufs_touched; + unsigned long subbufs_lost; + unsigned long subbufs_read; + + struct { + unsigned long lost_events; + __u32 id; + __u32 read; + } reader; + + __u32 subbuf_size; + __u32 nr_subbufs; + + __u32 meta_page_size; + __u32 meta_struct_len; +}; + +#endif /* _TRACE_MMAP_H_ */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index db73e326fa04..e9ff1c95e896 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -338,6 +338,7 @@ struct buffer_page { local_t entries; /* entries on this page */ unsigned long real_end; /* real end of data */ unsigned order; /* order of the page */ + u32 id; /* ID for external mapping */ struct buffer_data_page *page; /* Actual data page */ }; =20 @@ -484,6 +485,12 @@ struct ring_buffer_per_cpu { u64 read_stamp; /* pages removed since last reset */ unsigned long pages_removed; + + int mapped; + struct mutex mapping_lock; + unsigned long *subbuf_ids; /* ID to addr */ + struct trace_buffer_meta *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 */ @@ -1542,6 +1549,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, l= ong 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); =20 bpage =3D kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), GFP_KERNEL, cpu_to_node(cpu)); @@ -5160,6 +5168,23 @@ static void rb_clear_buffer_page(struct buffer_page = *page) page->read =3D 0; } =20 +static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct trace_buffer_meta *meta =3D cpu_buffer->meta_page; + + WRITE_ONCE(meta->entries, local_read(&cpu_buffer->entries)); + WRITE_ONCE(meta->overrun, local_read(&cpu_buffer->overrun)); + WRITE_ONCE(meta->read, cpu_buffer->read); + + WRITE_ONCE(meta->subbufs_touched, local_read(&cpu_buffer->pages_touched)); + WRITE_ONCE(meta->subbufs_lost, local_read(&cpu_buffer->pages_lost)); + WRITE_ONCE(meta->subbufs_read, local_read(&cpu_buffer->pages_read)); + + WRITE_ONCE(meta->reader.read, cpu_buffer->reader_page->read); + WRITE_ONCE(meta->reader.id, cpu_buffer->reader_page->id); + WRITE_ONCE(meta->reader.lost_events, cpu_buffer->lost_events); +} + static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) { @@ -5204,6 +5229,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->lost_events =3D 0; cpu_buffer->last_overrun =3D 0; =20 + if (cpu_buffer->mapped) + rb_update_meta_page(cpu_buffer); + rb_head_page_activate(cpu_buffer); cpu_buffer->pages_removed =3D 0; } @@ -5418,6 +5446,11 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer= _a, cpu_buffer_a =3D buffer_a->buffers[cpu]; cpu_buffer_b =3D buffer_b->buffers[cpu]; =20 + if (READ_ONCE(cpu_buffer_a->mapped) || READ_ONCE(cpu_buffer_b->mapped)) { + ret =3D -EBUSY; + goto out; + } + /* At least make sure the two buffers are somewhat the same */ if (cpu_buffer_a->nr_pages !=3D cpu_buffer_b->nr_pages) goto out; @@ -5682,7 +5715,8 @@ 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 =3D=3D cpu_buffer->commit_page) { + cpu_buffer->reader_page =3D=3D cpu_buffer->commit_page || + cpu_buffer->mapped) { struct buffer_data_page *rpage =3D cpu_buffer->reader_page->page; unsigned int rpos =3D read; unsigned int pos =3D 0; @@ -5901,6 +5935,11 @@ int ring_buffer_subbuf_order_set(struct trace_buffer= *buffer, int order) =20 cpu_buffer =3D buffer->buffers[cpu]; =20 + if (cpu_buffer->mapped) { + err =3D -EBUSY; + goto error; + } + /* Update the number of pages to match the new size */ nr_pages =3D old_size * buffer->buffers[cpu]->nr_pages; nr_pages =3D DIV_ROUND_UP(nr_pages, buffer->subbuf_size); @@ -6002,6 +6041,295 @@ int ring_buffer_subbuf_order_set(struct trace_buffe= r *buffer, int order) } EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set); =20 +#define subbuf_page(off, start) \ + virt_to_page((void *)(start + (off << PAGE_SHIFT))) + +#define foreach_subbuf_page(sub_order, start, page) \ + page =3D subbuf_page(0, (start)); \ + for (int __off =3D 0; __off < (1 << (sub_order)); \ + __off++, page =3D subbuf_page(__off, (start))) + +static inline void subbuf_map_prepare(unsigned long subbuf_start, int orde= r) +{ + struct page *page; + + /* + * When allocating order > 0 pages, only the first struct page has a + * refcount > 1. Increasing the refcount here ensures none of the struct + * page composing the sub-buffer is freeed when the mapping is closed. + */ + foreach_subbuf_page(order, subbuf_start, page) + page_ref_inc(page); +} + +static inline void subbuf_unmap(unsigned long subbuf_start, int order) +{ + struct page *page; + + foreach_subbuf_page(order, subbuf_start, page) { + page_ref_dec(page); + page->mapping =3D NULL; + } +} + +static void rb_free_subbuf_ids(struct ring_buffer_per_cpu *cpu_buffer) +{ + int sub_id; + + for (sub_id =3D 0; sub_id < cpu_buffer->nr_pages + 1; sub_id++) + subbuf_unmap(cpu_buffer->subbuf_ids[sub_id], + cpu_buffer->buffer->subbuf_order); + + kfree(cpu_buffer->subbuf_ids); + cpu_buffer->subbuf_ids =3D 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 =3D page_to_virt(alloc_page(GFP_USER | __GFP_ZERO)); + 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 =3D (unsigned long)cpu_buffer->meta_page; + + virt_to_page((void *)addr)->mapping =3D NULL; + free_page(addr); + cpu_buffer->meta_page =3D NULL; +} + +static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, + unsigned long *subbuf_ids) +{ + struct trace_buffer_meta *meta =3D cpu_buffer->meta_page; + unsigned int nr_subbufs =3D cpu_buffer->nr_pages + 1; + struct buffer_page *first_subbuf, *subbuf; + int id =3D 0; + + subbuf_ids[id] =3D (unsigned long)cpu_buffer->reader_page->page; + subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order); + cpu_buffer->reader_page->id =3D id++; + + first_subbuf =3D subbuf =3D rb_set_head_page(cpu_buffer); + do { + if (id >=3D nr_subbufs) { + WARN_ON(1); + break; + } + + subbuf_ids[id] =3D (unsigned long)subbuf->page; + subbuf->id =3D id; + subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order); + + rb_inc_page(&subbuf); + id++; + } while (subbuf !=3D first_subbuf); + + /* install subbuf ID to kern VA translation */ + cpu_buffer->subbuf_ids =3D subbuf_ids; + + meta->meta_page_size =3D PAGE_SIZE; + meta->meta_struct_len =3D sizeof(*meta); + meta->nr_subbufs =3D nr_subbufs; + meta->subbuf_size =3D cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE; + + rb_update_meta_page(cpu_buffer); +} + +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 =3D 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_bu= ffer) +{ + 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, *subbuf_ids; + int err =3D 0; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer =3D buffer->buffers[cpu]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (cpu_buffer->mapped) { + if (cpu_buffer->mapped =3D=3D INT_MAX) + err =3D -EBUSY; + else + WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped + 1); + mutex_unlock(&cpu_buffer->mapping_lock); + return err; + } + + /* prevent another thread from changing buffer sizes */ + mutex_lock(&buffer->mutex); + + err =3D rb_alloc_meta_page(cpu_buffer); + if (err) + goto unlock; + + /* subbuf_ids include the reader while nr_pages does not */ + subbuf_ids =3D kzalloc(sizeof(*subbuf_ids) * (cpu_buffer->nr_pages + 1), + GFP_KERNEL); + if (!subbuf_ids) { + rb_free_meta_page(cpu_buffer); + err =3D -ENOMEM; + goto unlock; + } + + atomic_inc(&cpu_buffer->resize_disabled); + + /* + * Lock all readers to block any subbuf swap until the subbuf IDs are + * assigned. + */ + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + + rb_setup_ids_meta_page(cpu_buffer, subbuf_ids); + + WRITE_ONCE(cpu_buffer->mapped, 1); + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); +unlock: + mutex_unlock(&buffer->mutex); + 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 =3D 0; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer =3D buffer->buffers[cpu]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (!cpu_buffer->mapped) { + err =3D -ENODEV; + goto unlock; + } + + WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped - 1); + if (!cpu_buffer->mapped) { + /* Wait for the writer and readers to observe !mapped */ + synchronize_rcu(); + + rb_free_subbuf_ids(cpu_buffer); + rb_free_meta_page(cpu_buffer); + atomic_dec(&cpu_buffer->resize_disabled); + } +unlock: + mutex_unlock(&cpu_buffer->mapping_lock); + + return err; +} + +/* + * +--------------+ pgoff =3D=3D 0 + * | meta page | + * +--------------+ pgoff =3D=3D 1 + * | subbuffer 0 | + * +--------------+ pgoff =3D=3D 1 + (1 << subbuf_order) + * | subbuffer 1 | + * ... + */ +struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu, + unsigned long pgoff) +{ + struct ring_buffer_per_cpu *cpu_buffer =3D buffer->buffers[cpu]; + unsigned long subbuf_id, subbuf_offset, addr; + struct page *page; + + if (!pgoff) + return virt_to_page((void *)cpu_buffer->meta_page); + + pgoff--; + + subbuf_id =3D pgoff >> buffer->subbuf_order; + if (subbuf_id > cpu_buffer->nr_pages) + return NULL; + + subbuf_offset =3D pgoff & ((1UL << buffer->subbuf_order) - 1); + addr =3D cpu_buffer->subbuf_ids[subbuf_id] + (subbuf_offset * PAGE_SIZE); + page =3D virt_to_page((void *)addr); + + return page; +} + +int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long reader_size; + unsigned long flags; + + cpu_buffer =3D 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); +consume: + if (rb_per_cpu_empty(cpu_buffer)) + goto out; + + reader_size =3D rb_page_size(cpu_buffer->reader_page); + + /* + * There are data to be read on the current reader page, we can + * return to the caller. But before that, we assume the latter will read + * everything. Let's update the kernel reader accordingly. + */ + if (cpu_buffer->reader_page->read < reader_size) { + while (cpu_buffer->reader_page->read < reader_size) + rb_advance_reader(cpu_buffer); + goto out; + } + + if (WARN_ON(!rb_get_reader_page(cpu_buffer))) + goto out; + + goto consume; +out: + rb_update_meta_page(cpu_buffer); + 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 --=20 2.43.0.275.g3460e3d667-goog