[1/2] ring-buffer: Introducing ring-buffer mapping functions

Message ID	20230317143310.1604700-2-vdonnefort@google.com (mailing list archive)
State	Superseded
Headers	show Return-Path: <linux-trace-kernel-owner@vger.kernel.org> Date: Fri, 17 Mar 2023 14:33:09 +0000 In-Reply-To: <20230317143310.1604700-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230317143310.1604700-1-vdonnefort@google.com> Message-ID: <20230317143310.1604700-2-vdonnefort@google.com> Subject: [PATCH 1/2] ring-buffer: Introducing ring-buffer mapping functions From: Vincent Donnefort <vdonnefort@google.com> 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 <vdonnefort@google.com> Content-Type: text/plain; charset="UTF-8" Precedence: bulk
Series	Introducing trace buffer mapping by user-space \| expand [0/2] Introducing trace buffer mapping by user-space [1/2] ring-buffer: Introducing ring-buffer mapping functions [2/2] tracing: Allow user-space mapping of the ring-buffer

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 <linux/seq_file.h> #include <linux/poll.h> +#include <uapi/linux/trace_mmap.h> + 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..b5caed17a066 --- /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 <asm/bitsperlong.h> + +#include <linux/types.h> + +struct ring_buffer_meta_page { +#if __BITS_PER_LONG == 64 + __u64 entries; + __u64 overrun; +#else + __u32 entries; + __u32 overrun; +#endif + __u32 pages_touched; + __u32 reader_page; + __u32 nr_data_pages; /* doesn't take into account the reader_page */ + __u32 data_page_head; /* index of data_pages[] */ + __u32 data_pages[]; +}; + +#endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index af50d931b020..08765310380b 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_page *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 +1459,37 @@ 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) +{ + unsigned long head_id; + + if (!READ_ONCE(cpu_buffer->mapped)) + return; + + head_id = cpu_buffer->meta_page->data_page_head; + cpu_buffer->meta_page->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; + + if (!READ_ONCE(cpu_buffer->mapped)) + return; + + meta->reader_page = cpu_buffer->head_page->id; + meta->data_pages[meta->data_page_head] = cpu_buffer->reader_page->id; +} + 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 +1511,12 @@ 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); } @@ -1567,6 +1602,13 @@ 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 +1777,7 @@ 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 +2216,6 @@ 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 +2565,13 @@ 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 +3228,14 @@ 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 +3539,7 @@ 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; @@ -4643,7 +4700,9 @@ 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); + rb_meta_page_head_move(cpu_buffer, 1); local_inc(&cpu_buffer->pages_read); @@ -5285,6 +5344,12 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->lost_events = 0; cpu_buffer->last_overrun = 0; + if (READ_ONCE(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); + } + rb_head_page_activate(cpu_buffer); } @@ -5489,6 +5554,11 @@ 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 +5792,8 @@ 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 || + READ_ONCE(cpu_buffer->mapped)) { struct buffer_data_page *rpage = cpu_buffer->reader_page->page; unsigned int rpos = read; unsigned int pos = 0; @@ -5839,6 +5910,263 @@ 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 > 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_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, + unsigned long *page_ids) +{ + struct ring_buffer_meta_page *meta = cpu_buffer->meta_page; + 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 > META_PAGE_MAX_PAGES) { + WARN_ON(1); + break; + } + + page_ids[id] = (unsigned long)bpage->page; + bpage->id = id; + meta->data_pages[id - 1] = 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->reader_page = cpu_buffer->reader_page->id; + meta->nr_data_pages = cpu_buffer->nr_pages; + meta->data_page_head = 0; +} + +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 | 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 = buffer->buffers[cpu]; + + if (!pgoff) + return virt_to_page(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; + struct buffer_page *reader; + 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); + reader = cpu_buffer->reader_page; + reader->read = rb_page_size(reader); + if (!rb_per_cpu_empty(cpu_buffer)) + WARN_ON(!rb_get_reader_page(cpu_buffer)); + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + + rb_put_mapped_buffer(cpu_buffer); + + return 0; +} + +int ring_buffer_update_meta_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 PTR_ERR(cpu_buffer); + + /* 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); + + 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

[1/2] ring-buffer: Introducing ring-buffer mapping functions

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