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AJvYcCXbFJpwBTjE3JEO5WiDc75JOgqxVtuv56IPxKB2U4aC3RlQkJgZfIhx8w2Wh4NbtKjTbJo9kAmjF8+TDh62gqYtuOM= X-Gm-Message-State: AOJu0YwCXICDsR68d+Z8n3p1jg8lvfkXPTimTscS6ZbWt8/454D7UEI9 9B964L0dy/MLSZFnTVrTUZohJPEwSwKrc824BAG3B22OHIY7MABO/RwFoXnZthVRQ/n8hFJMRm0 WHTwjl+faNLmQrdzcRQ== X-Google-Smtp-Source: AGHT+IEI68VxNWVakxnGq4gE6qTAXewGqFHFSYPNX1RA6cXedzSDwgp6GpSwURG/LWsTyt/ZAwxDwIJIy9SkLc87 X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a81:fe0f:0:b0:61b:ebf1:77a with SMTP id j15-20020a81fe0f000000b0061bebf1077amr242849ywn.0.1714475643635; Tue, 30 Apr 2024 04:14:03 -0700 (PDT) Date: Tue, 30 Apr 2024 12:13:51 +0100 In-Reply-To: <20240430111354.637356-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20240430111354.637356-1-vdonnefort@google.com> X-Mailer: git-send-email 2.44.0.769.g3c40516874-goog Message-ID: <20240430111354.637356-3-vdonnefort@google.com> Subject: [PATCH v22 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, rdunlap@infradead.org, rppt@kernel.org, david@redhat.com, Vincent Donnefort , linux-mm@kvack.org X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: B9303A0028 X-Stat-Signature: a7c65w8qqkdb7q8wqc8ei5grc9nujisi X-Rspam-User: X-HE-Tag: 1714475644-499839 X-HE-Meta: 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 a9+uqjXX 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: In preparation for allowing the user-space to map a ring-buffer, add a set of mapping functions: ring_buffer_{map,unmap}() 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. CC: Signed-off-by: Vincent Donnefort Acked-by: David Hildenbrand diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index dc5ae4e96aee..96d2140b471e 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; @@ -223,4 +225,8 @@ 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, + struct vm_area_struct *vma); +int ring_buffer_unmap(struct trace_buffer *buffer, int cpu); +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_mmap.h new file mode 100644 index 000000000000..b682e9925539 --- /dev/null +++ b/include/uapi/linux/trace_mmap.h @@ -0,0 +1,46 @@ +/* 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 + * @meta_page_size: Size of this meta-page. + * @meta_struct_len: Size of this structure. + * @subbuf_size: Size of each sub-buffer. + * @nr_subbufs: Number of subbfs in the ring-buffer, including the reader. + * @reader.lost_events: Number of events lost at the time of the reader swap. + * @reader.id: subbuf ID of the current reader. ID range [0 : @nr_subbufs - 1] + * @reader.read: Number of bytes read on the reader subbuf. + * @flags: Placeholder for now, 0 until new features are supported. + * @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. + * @Reserved1: Internal use only. + * @Reserved2: Internal use only. + */ +struct trace_buffer_meta { + __u32 meta_page_size; + __u32 meta_struct_len; + + __u32 subbuf_size; + __u32 nr_subbufs; + + struct { + __u64 lost_events; + __u32 id; + __u32 read; + } reader; + + __u64 flags; + + __u64 entries; + __u64 overrun; + __u64 read; + + __u64 Reserved1; + __u64 Reserved2; +}; + +#endif /* _TRACE_MMAP_H_ */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index cc9ebe593571..fc66d01ff472 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -26,6 +27,7 @@ #include #include #include +#include #include #include @@ -338,6 +340,7 @@ 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 */ }; @@ -484,6 +487,12 @@ struct ring_buffer_per_cpu { u64 read_stamp; /* pages removed since last reset */ unsigned long pages_removed; + + unsigned int mapped; + struct mutex mapping_lock; + unsigned long *subbuf_ids; /* ID to subbuf VA */ + 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 */ @@ -1599,6 +1608,7 @@ 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)); @@ -1789,8 +1799,6 @@ bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer) return buffer->time_stamp_abs; } -static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer); - static inline unsigned long rb_page_entries(struct buffer_page *bpage) { return local_read(&bpage->entries) & RB_WRITE_MASK; @@ -5211,6 +5219,22 @@ static void rb_clear_buffer_page(struct buffer_page *page) page->read = 0; } +static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct trace_buffer_meta *meta = cpu_buffer->meta_page; + + meta->reader.read = cpu_buffer->reader_page->read; + meta->reader.id = cpu_buffer->reader_page->id; + meta->reader.lost_events = cpu_buffer->lost_events; + + meta->entries = local_read(&cpu_buffer->entries); + meta->overrun = local_read(&cpu_buffer->overrun); + meta->read = cpu_buffer->read; + + /* Some archs do not have data cache coherency between kernel and user-space */ + flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page)); +} + static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) { @@ -5255,6 +5279,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->lost_events = 0; cpu_buffer->last_overrun = 0; + if (cpu_buffer->mapped) + rb_update_meta_page(cpu_buffer); + rb_head_page_activate(cpu_buffer); cpu_buffer->pages_removed = 0; } @@ -5469,6 +5496,12 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, cpu_buffer_a = buffer_a->buffers[cpu]; cpu_buffer_b = buffer_b->buffers[cpu]; + /* It's up to the callers to not try to swap mapped buffers */ + if (WARN_ON_ONCE(cpu_buffer_a->mapped || 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; @@ -5733,7 +5766,8 @@ 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; @@ -5956,6 +5990,11 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) cpu_buffer = buffer->buffers[cpu]; + if (cpu_buffer->mapped) { + err = -EBUSY; + goto error; + } + /* Update the number of pages to match the new size */ nr_pages = old_size * buffer->buffers[cpu]->nr_pages; nr_pages = DIV_ROUND_UP(nr_pages, buffer->subbuf_size); @@ -6057,6 +6096,370 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) } EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set); +static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct page *page; + + if (cpu_buffer->meta_page) + return 0; + + page = alloc_page(GFP_USER | __GFP_ZERO); + if (!page) + return -ENOMEM; + + cpu_buffer->meta_page = page_to_virt(page); + + return 0; +} + +static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + unsigned long addr = (unsigned long)cpu_buffer->meta_page; + + free_page(addr); + cpu_buffer->meta_page = NULL; +} + +static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, + unsigned long *subbuf_ids) +{ + struct trace_buffer_meta *meta = cpu_buffer->meta_page; + unsigned int nr_subbufs = cpu_buffer->nr_pages + 1; + struct buffer_page *first_subbuf, *subbuf; + int id = 0; + + subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page; + cpu_buffer->reader_page->id = id++; + + first_subbuf = subbuf = rb_set_head_page(cpu_buffer); + do { + if (WARN_ON(id >= nr_subbufs)) + break; + + subbuf_ids[id] = (unsigned long)subbuf->page; + subbuf->id = id; + + rb_inc_page(&subbuf); + id++; + } while (subbuf != first_subbuf); + + /* install subbuf ID to kern VA translation */ + cpu_buffer->subbuf_ids = subbuf_ids; + + meta->meta_page_size = PAGE_SIZE; + meta->meta_struct_len = sizeof(*meta); + meta->nr_subbufs = nr_subbufs; + meta->subbuf_size = cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE; + + rb_update_meta_page(cpu_buffer); +} + +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]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (!cpu_buffer->mapped) { + mutex_unlock(&cpu_buffer->mapping_lock); + return ERR_PTR(-ENODEV); + } + + return cpu_buffer; +} + +static void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer) +{ + mutex_unlock(&cpu_buffer->mapping_lock); +} + +/* + * Fast-path for rb_buffer_(un)map(). Called whenever the meta-page doesn't need + * to be set-up or torn-down. + */ +static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer, + bool inc) +{ + unsigned long flags; + + lockdep_assert_held(&cpu_buffer->mapping_lock); + + if (inc && cpu_buffer->mapped == UINT_MAX) + return -EBUSY; + + if (WARN_ON(!inc && cpu_buffer->mapped == 0)) + return -EINVAL; + + mutex_lock(&cpu_buffer->buffer->mutex); + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + + if (inc) + cpu_buffer->mapped++; + else + cpu_buffer->mapped--; + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + mutex_unlock(&cpu_buffer->buffer->mutex); + + return 0; +} + +/* + * +--------------+ pgoff == 0 + * | meta page | + * +--------------+ pgoff == 1 + * | subbuffer 0 | + * | | + * +--------------+ pgoff == (1 + (1 << subbuf_order)) + * | subbuffer 1 | + * | | + * ... + */ +#ifdef CONFIG_MMU +static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, + struct vm_area_struct *vma) +{ + unsigned long nr_subbufs, nr_pages, vma_pages, pgoff = vma->vm_pgoff; + unsigned int subbuf_pages, subbuf_order; + struct page **pages; + int p = 0, s = 0; + int err; + + /* Refuse MP_PRIVATE or writable mappings */ + if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC || + !(vma->vm_flags & VM_MAYSHARE)) + return -EPERM; + + /* + * Make sure the mapping cannot become writable later. Also tell the VM + * to not touch these pages (VM_DONTCOPY | VM_DONTEXPAND). Finally, + * prevent migration, GUP and dump (VM_IO). + */ + vm_flags_mod(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_IO, VM_MAYWRITE); + + lockdep_assert_held(&cpu_buffer->mapping_lock); + + subbuf_order = cpu_buffer->buffer->subbuf_order; + subbuf_pages = 1 << subbuf_order; + + nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */ + nr_pages = ((nr_subbufs) << subbuf_order) - pgoff + 1; /* + meta-page */ + + vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT; + if (!vma_pages || vma_pages > nr_pages) + return -EINVAL; + + nr_pages = vma_pages; + + pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL); + if (!pages) + return -ENOMEM; + + if (!pgoff) { + pages[p++] = virt_to_page(cpu_buffer->meta_page); + + /* + * TODO: Align sub-buffers on their size, once + * vm_insert_pages() supports the zero-page. + */ + } else { + /* Skip the meta-page */ + pgoff--; + + if (pgoff % subbuf_pages) { + err = -EINVAL; + goto out; + } + + s += pgoff / subbuf_pages; + } + + while (s < nr_subbufs && p < nr_pages) { + struct page *page = virt_to_page(cpu_buffer->subbuf_ids[s]); + int off = 0; + + for (; off < (1 << (subbuf_order)); off++, page++) { + if (p >= nr_pages) + break; + + pages[p++] = page; + } + s++; + } + + err = vm_insert_pages(vma, vma->vm_start, pages, &nr_pages); + +out: + kfree(pages); + + return err; +} +#else +static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, + struct vm_area_struct *vma) +{ + return -EOPNOTSUPP; +} +#endif + +int ring_buffer_map(struct trace_buffer *buffer, int cpu, + struct vm_area_struct *vma) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long flags, *subbuf_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) { + err = __rb_map_vma(cpu_buffer, vma); + if (!err) + err = __rb_inc_dec_mapped(cpu_buffer, true); + mutex_unlock(&cpu_buffer->mapping_lock); + return err; + } + + /* prevent another thread from changing buffer/sub-buffer sizes */ + mutex_lock(&buffer->mutex); + + err = rb_alloc_meta_page(cpu_buffer); + if (err) + goto unlock; + + /* subbuf_ids include the reader while nr_pages does not */ + subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP_KERNEL); + if (!subbuf_ids) { + rb_free_meta_page(cpu_buffer); + err = -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); + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + + err = __rb_map_vma(cpu_buffer, vma); + if (!err) { + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + cpu_buffer->mapped = 1; + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + } else { + kfree(cpu_buffer->subbuf_ids); + cpu_buffer->subbuf_ids = NULL; + rb_free_meta_page(cpu_buffer); + } + +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; + unsigned long flags; + 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 out; + } else if (cpu_buffer->mapped > 1) { + __rb_inc_dec_mapped(cpu_buffer, false); + goto out; + } + + mutex_lock(&buffer->mutex); + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + + cpu_buffer->mapped = 0; + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + + kfree(cpu_buffer->subbuf_ids); + cpu_buffer->subbuf_ids = NULL; + rb_free_meta_page(cpu_buffer); + atomic_dec(&cpu_buffer->resize_disabled); + + mutex_unlock(&buffer->mutex); + +out: + mutex_unlock(&cpu_buffer->mapping_lock); + + return err; +} + +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 = 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 = 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: + /* Some archs do not have data cache coherency between kernel and user-space */ + flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page)); + + 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 From patchwork Tue Apr 30 11:13:52 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13648770 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id AE9AFC19F53 for ; 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AJvYcCUrdgzSkxB5i1KZF9tu1FpeenjJJ2EuevEg9zhN4K2hnkO28Etsd6sQ5baYJwjENgko18wgm9o5PEFpjBWtqucMxJo= X-Gm-Message-State: AOJu0YxF+hb1yeA3WNMvRsDTdgZEP34Vph8etuD64jlLKJuE6W+t27gi vg8wMXi4rQPZTGGsF5hOxSpoalEDv0FH/5yiLbNAqylfUoC6WotBqxtTl/4RMJ01dwYvbfR7PIO GHrqajsAPe+KrKFnrAw== X-Google-Smtp-Source: AGHT+IEO2pWfjDCnEIaI11osu0vpD76LPQlxnP+vniPkBaaF4f948j34AMtRFw57ax5xp982MlQPZiRKqJXvorKB X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a5d:5850:0:b0:34d:17e1:7eed with SMTP id i16-20020a5d5850000000b0034d17e17eedmr22593wrf.3.1714475646019; Tue, 30 Apr 2024 04:14:06 -0700 (PDT) Date: Tue, 30 Apr 2024 12:13:52 +0100 In-Reply-To: <20240430111354.637356-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20240430111354.637356-1-vdonnefort@google.com> X-Mailer: git-send-email 2.44.0.769.g3c40516874-goog Message-ID: <20240430111354.637356-4-vdonnefort@google.com> Subject: [PATCH v22 3/5] 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: mathieu.desnoyers@efficios.com, kernel-team@android.com, rdunlap@infradead.org, rppt@kernel.org, david@redhat.com, Vincent Donnefort , linux-mm@kvack.org X-Stat-Signature: cyhnaamfkdgxgbzdkqm4o9nb8gph57po X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: BD9C180018 X-HE-Tag: 1714475647-684778 X-HE-Meta: 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 APhw9PTR 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 is exposed via the per-CPU file trace_pipe_raw. The first element of the mapping is the meta-page. It is followed by each subbuffer constituting the ring-buffer, ordered by their unique page ID: * Meta-page -- include/uapi/linux/trace_mmap.h for a description * Subbuf ID 0 * Subbuf ID 1 ... It is therefore easy to translate a subbuf ID into an offset in the mapping: reader_id = meta->reader->id; reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size; When new data is available, the mapper must call a newly introduced ioctl: TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to point to the next reader containing unread data. Mapping will prevent snapshot and buffer size modifications. CC: Signed-off-by: Vincent Donnefort diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h index b682e9925539..bd1066754220 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -43,4 +43,6 @@ struct trace_buffer_meta { __u64 Reserved2; }; +#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1) + #endif /* _TRACE_MMAP_H_ */ diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 233d1af39fff..a35e7f598233 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -1191,6 +1191,12 @@ static void tracing_snapshot_instance_cond(struct trace_array *tr, return; } + if (tr->mapped) { + trace_array_puts(tr, "*** BUFFER MEMORY MAPPED ***\n"); + trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n"); + return; + } + local_irq_save(flags); update_max_tr(tr, current, smp_processor_id(), cond_data); local_irq_restore(flags); @@ -1323,7 +1329,7 @@ static int tracing_arm_snapshot_locked(struct trace_array *tr) lockdep_assert_held(&trace_types_lock); spin_lock(&tr->snapshot_trigger_lock); - if (tr->snapshot == UINT_MAX) { + if (tr->snapshot == UINT_MAX || tr->mapped) { spin_unlock(&tr->snapshot_trigger_lock); return -EBUSY; } @@ -6068,7 +6074,7 @@ 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) @@ -8194,15 +8200,32 @@ 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; + int err; + + if (cmd == TRACE_MMAP_IOCTL_GET_READER) { + if (!(file->f_flags & O_NONBLOCK)) { + err = ring_buffer_wait(iter->array_buffer->buffer, + iter->cpu_file, + iter->tr->buffer_percent, + NULL, NULL); + if (err) + return err; + } - if (cmd) - return -ENOIOCTLCMD; + return ring_buffer_map_get_reader(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); /* Make sure the waiters see the new wait_index */ @@ -8214,6 +8237,76 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned return 0; } +#ifdef CONFIG_TRACER_MAX_TRACE +static int get_snapshot_map(struct trace_array *tr) +{ + int err = 0; + + /* + * Called with mmap_lock held. lockdep would be unhappy if we would now + * take trace_types_lock. Instead use the specific + * snapshot_trigger_lock. + */ + spin_lock(&tr->snapshot_trigger_lock); + + if (tr->snapshot || tr->mapped == UINT_MAX) + err = -EBUSY; + else + tr->mapped++; + + spin_unlock(&tr->snapshot_trigger_lock); + + /* Wait for update_max_tr() to observe iter->tr->mapped */ + if (tr->mapped == 1) + synchronize_rcu(); + + return err; + +} +static void put_snapshot_map(struct trace_array *tr) +{ + spin_lock(&tr->snapshot_trigger_lock); + if (!WARN_ON(!tr->mapped)) + tr->mapped--; + spin_unlock(&tr->snapshot_trigger_lock); +} +#else +static inline int get_snapshot_map(struct trace_array *tr) { return 0; } +static inline void put_snapshot_map(struct trace_array *tr) { } +#endif + +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; + + WARN_ON(ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file)); + put_snapshot_map(iter->tr); +} + +static const struct vm_operations_struct tracing_buffers_vmops = { + .close = tracing_buffers_mmap_close, +}; + +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; + int ret = 0; + + ret = get_snapshot_map(iter->tr); + if (ret) + return ret; + + ret = ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file, vma); + if (ret) + put_snapshot_map(iter->tr); + + vma->vm_ops = &tracing_buffers_vmops; + + return ret; +} + static const struct file_operations tracing_buffers_fops = { .open = tracing_buffers_open, .read = tracing_buffers_read, @@ -8223,6 +8316,7 @@ 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 diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 64450615ca0c..749a182dab48 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -336,6 +336,7 @@ struct trace_array { bool allocated_snapshot; spinlock_t snapshot_trigger_lock; unsigned int snapshot; + unsigned int mapped; unsigned long max_latency; #ifdef CONFIG_FSNOTIFY struct dentry *d_max_latency;