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ring-buffer: Introducing ring-buffer mapping functions
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.
Link: https://lore.kernel.org/linux-trace-kernel/20240510140435.3550353-3-vdonnefort@google.com
CC: <linux-mm@kvack.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Vincent Donnefort
Steven Rostedt (Google)
parent
c09d4167b5
commit
117c39200d
3 changed files with 463 additions and 3 deletions
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@ -6,6 +6,8 @@
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#include <linux/seq_file.h>
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#include <linux/poll.h>
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#include <uapi/linux/trace_mmap.h>
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struct trace_buffer;
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struct ring_buffer_iter;
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@ -223,4 +225,8 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node);
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#define trace_rb_cpu_prepare NULL
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#endif
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int ring_buffer_map(struct trace_buffer *buffer, int cpu,
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struct vm_area_struct *vma);
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int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
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int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
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#endif /* _LINUX_RING_BUFFER_H */
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46
include/uapi/linux/trace_mmap.h
Normal file
46
include/uapi/linux/trace_mmap.h
Normal file
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@ -0,0 +1,46 @@
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/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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#ifndef _TRACE_MMAP_H_
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#define _TRACE_MMAP_H_
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#include <linux/types.h>
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/**
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* struct trace_buffer_meta - Ring-buffer Meta-page description
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* @meta_page_size: Size of this meta-page.
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* @meta_struct_len: Size of this structure.
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* @subbuf_size: Size of each sub-buffer.
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* @nr_subbufs: Number of subbfs in the ring-buffer, including the reader.
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* @reader.lost_events: Number of events lost at the time of the reader swap.
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* @reader.id: subbuf ID of the current reader. ID range [0 : @nr_subbufs - 1]
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* @reader.read: Number of bytes read on the reader subbuf.
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* @flags: Placeholder for now, 0 until new features are supported.
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* @entries: Number of entries in the ring-buffer.
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* @overrun: Number of entries lost in the ring-buffer.
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* @read: Number of entries that have been read.
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* @Reserved1: Internal use only.
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* @Reserved2: Internal use only.
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*/
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struct trace_buffer_meta {
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__u32 meta_page_size;
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__u32 meta_struct_len;
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__u32 subbuf_size;
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__u32 nr_subbufs;
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struct {
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__u64 lost_events;
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__u32 id;
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__u32 read;
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} reader;
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__u64 flags;
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__u64 entries;
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__u64 overrun;
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__u64 read;
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__u64 Reserved1;
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__u64 Reserved2;
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};
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#endif /* _TRACE_MMAP_H_ */
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@ -9,6 +9,7 @@
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#include <linux/ring_buffer.h>
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#include <linux/trace_clock.h>
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#include <linux/sched/clock.h>
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#include <linux/cacheflush.h>
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#include <linux/trace_seq.h>
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#include <linux/spinlock.h>
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#include <linux/irq_work.h>
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@ -26,6 +27,7 @@
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#include <linux/list.h>
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#include <linux/cpu.h>
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#include <linux/oom.h>
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#include <linux/mm.h>
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#include <asm/local64.h>
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#include <asm/local.h>
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@ -338,6 +340,7 @@ struct buffer_page {
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local_t entries; /* entries on this page */
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unsigned long real_end; /* real end of data */
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unsigned order; /* order of the page */
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u32 id; /* ID for external mapping */
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struct buffer_data_page *page; /* Actual data page */
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};
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@ -484,6 +487,12 @@ struct ring_buffer_per_cpu {
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u64 read_stamp;
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/* pages removed since last reset */
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unsigned long pages_removed;
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unsigned int mapped;
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struct mutex mapping_lock;
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unsigned long *subbuf_ids; /* ID to subbuf VA */
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struct trace_buffer_meta *meta_page;
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/* ring buffer pages to update, > 0 to add, < 0 to remove */
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long nr_pages_to_update;
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struct list_head new_pages; /* new pages to add */
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@ -1599,6 +1608,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
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init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
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init_waitqueue_head(&cpu_buffer->irq_work.waiters);
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init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
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mutex_init(&cpu_buffer->mapping_lock);
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bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
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GFP_KERNEL, cpu_to_node(cpu));
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@ -1789,8 +1799,6 @@ bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer)
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return buffer->time_stamp_abs;
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}
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static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
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static inline unsigned long rb_page_entries(struct buffer_page *bpage)
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{
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return local_read(&bpage->entries) & RB_WRITE_MASK;
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@ -5211,6 +5219,22 @@ static void rb_clear_buffer_page(struct buffer_page *page)
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page->read = 0;
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}
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static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
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{
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struct trace_buffer_meta *meta = cpu_buffer->meta_page;
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meta->reader.read = cpu_buffer->reader_page->read;
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meta->reader.id = cpu_buffer->reader_page->id;
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meta->reader.lost_events = cpu_buffer->lost_events;
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meta->entries = local_read(&cpu_buffer->entries);
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meta->overrun = local_read(&cpu_buffer->overrun);
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meta->read = cpu_buffer->read;
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/* Some archs do not have data cache coherency between kernel and user-space */
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flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page));
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}
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static void
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rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
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{
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@ -5255,6 +5279,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
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cpu_buffer->lost_events = 0;
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cpu_buffer->last_overrun = 0;
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if (cpu_buffer->mapped)
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rb_update_meta_page(cpu_buffer);
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rb_head_page_activate(cpu_buffer);
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cpu_buffer->pages_removed = 0;
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}
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@ -5469,6 +5496,12 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a,
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cpu_buffer_a = buffer_a->buffers[cpu];
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cpu_buffer_b = buffer_b->buffers[cpu];
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/* It's up to the callers to not try to swap mapped buffers */
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if (WARN_ON_ONCE(cpu_buffer_a->mapped || cpu_buffer_b->mapped)) {
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ret = -EBUSY;
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goto out;
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}
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/* At least make sure the two buffers are somewhat the same */
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if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
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goto out;
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@ -5733,7 +5766,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
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* Otherwise, we can simply swap the page with the one passed in.
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*/
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if (read || (len < (commit - read)) ||
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cpu_buffer->reader_page == cpu_buffer->commit_page) {
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cpu_buffer->reader_page == cpu_buffer->commit_page ||
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cpu_buffer->mapped) {
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struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
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unsigned int rpos = read;
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unsigned int pos = 0;
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@ -5956,6 +5990,11 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
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cpu_buffer = buffer->buffers[cpu];
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if (cpu_buffer->mapped) {
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err = -EBUSY;
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goto error;
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}
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/* Update the number of pages to match the new size */
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nr_pages = old_size * buffer->buffers[cpu]->nr_pages;
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nr_pages = DIV_ROUND_UP(nr_pages, buffer->subbuf_size);
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@ -6057,6 +6096,375 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
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}
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EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
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static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
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{
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struct page *page;
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if (cpu_buffer->meta_page)
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return 0;
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page = alloc_page(GFP_USER | __GFP_ZERO);
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if (!page)
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return -ENOMEM;
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cpu_buffer->meta_page = page_to_virt(page);
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return 0;
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}
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static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
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{
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unsigned long addr = (unsigned long)cpu_buffer->meta_page;
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free_page(addr);
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cpu_buffer->meta_page = NULL;
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}
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static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
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unsigned long *subbuf_ids)
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{
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struct trace_buffer_meta *meta = cpu_buffer->meta_page;
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unsigned int nr_subbufs = cpu_buffer->nr_pages + 1;
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struct buffer_page *first_subbuf, *subbuf;
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int id = 0;
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subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page;
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cpu_buffer->reader_page->id = id++;
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first_subbuf = subbuf = rb_set_head_page(cpu_buffer);
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do {
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if (WARN_ON(id >= nr_subbufs))
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break;
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subbuf_ids[id] = (unsigned long)subbuf->page;
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subbuf->id = id;
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rb_inc_page(&subbuf);
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id++;
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} while (subbuf != first_subbuf);
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/* install subbuf ID to kern VA translation */
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cpu_buffer->subbuf_ids = subbuf_ids;
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meta->meta_page_size = PAGE_SIZE;
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meta->meta_struct_len = sizeof(*meta);
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meta->nr_subbufs = nr_subbufs;
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meta->subbuf_size = cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE;
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rb_update_meta_page(cpu_buffer);
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}
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static struct ring_buffer_per_cpu *
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rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu)
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{
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struct ring_buffer_per_cpu *cpu_buffer;
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if (!cpumask_test_cpu(cpu, buffer->cpumask))
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return ERR_PTR(-EINVAL);
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cpu_buffer = buffer->buffers[cpu];
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mutex_lock(&cpu_buffer->mapping_lock);
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if (!cpu_buffer->mapped) {
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mutex_unlock(&cpu_buffer->mapping_lock);
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return ERR_PTR(-ENODEV);
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}
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return cpu_buffer;
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}
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static void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer)
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{
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mutex_unlock(&cpu_buffer->mapping_lock);
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}
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/*
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* Fast-path for rb_buffer_(un)map(). Called whenever the meta-page doesn't need
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* to be set-up or torn-down.
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*/
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static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer,
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bool inc)
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{
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unsigned long flags;
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lockdep_assert_held(&cpu_buffer->mapping_lock);
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if (inc && cpu_buffer->mapped == UINT_MAX)
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return -EBUSY;
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if (WARN_ON(!inc && cpu_buffer->mapped == 0))
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return -EINVAL;
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mutex_lock(&cpu_buffer->buffer->mutex);
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raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
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if (inc)
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cpu_buffer->mapped++;
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else
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cpu_buffer->mapped--;
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raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
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mutex_unlock(&cpu_buffer->buffer->mutex);
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return 0;
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}
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/*
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* +--------------+ pgoff == 0
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* | meta page |
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* +--------------+ pgoff == 1
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* | subbuffer 0 |
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* | |
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* +--------------+ pgoff == (1 + (1 << subbuf_order))
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* | subbuffer 1 |
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* | |
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* ...
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*/
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#ifdef CONFIG_MMU
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static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
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struct vm_area_struct *vma)
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{
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unsigned long nr_subbufs, nr_pages, vma_pages, pgoff = vma->vm_pgoff;
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unsigned int subbuf_pages, subbuf_order;
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struct page **pages;
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int p = 0, s = 0;
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int err;
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/* Refuse MP_PRIVATE or writable mappings */
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if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC ||
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!(vma->vm_flags & VM_MAYSHARE))
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return -EPERM;
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/*
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* Make sure the mapping cannot become writable later. Also tell the VM
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* to not touch these pages (VM_DONTCOPY | VM_DONTEXPAND).
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*/
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vm_flags_mod(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP,
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VM_MAYWRITE);
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lockdep_assert_held(&cpu_buffer->mapping_lock);
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subbuf_order = cpu_buffer->buffer->subbuf_order;
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subbuf_pages = 1 << subbuf_order;
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nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */
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nr_pages = ((nr_subbufs) << subbuf_order) - pgoff + 1; /* + meta-page */
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vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
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if (!vma_pages || vma_pages > nr_pages)
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return -EINVAL;
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nr_pages = vma_pages;
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pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL);
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if (!pages)
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return -ENOMEM;
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if (!pgoff) {
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pages[p++] = virt_to_page(cpu_buffer->meta_page);
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/*
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* TODO: Align sub-buffers on their size, once
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* vm_insert_pages() supports the zero-page.
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*/
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} else {
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/* Skip the meta-page */
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pgoff--;
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if (pgoff % subbuf_pages) {
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err = -EINVAL;
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goto out;
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}
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s += pgoff / subbuf_pages;
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}
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while (p < nr_pages) {
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struct page *page = virt_to_page(cpu_buffer->subbuf_ids[s]);
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int off = 0;
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if (WARN_ON_ONCE(s >= nr_subbufs)) {
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err = -EINVAL;
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goto out;
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}
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for (; off < (1 << (subbuf_order)); off++, page++) {
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if (p >= nr_pages)
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break;
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pages[p++] = page;
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}
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s++;
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}
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err = vm_insert_pages(vma, vma->vm_start, pages, &nr_pages);
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out:
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kfree(pages);
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return err;
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}
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#else
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static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
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struct vm_area_struct *vma)
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{
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return -EOPNOTSUPP;
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}
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#endif
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int ring_buffer_map(struct trace_buffer *buffer, int cpu,
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struct vm_area_struct *vma)
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{
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struct ring_buffer_per_cpu *cpu_buffer;
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unsigned long flags, *subbuf_ids;
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int err = 0;
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|
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if (!cpumask_test_cpu(cpu, buffer->cpumask))
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return -EINVAL;
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cpu_buffer = buffer->buffers[cpu];
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mutex_lock(&cpu_buffer->mapping_lock);
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if (cpu_buffer->mapped) {
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err = __rb_map_vma(cpu_buffer, vma);
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if (!err)
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err = __rb_inc_dec_mapped(cpu_buffer, true);
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mutex_unlock(&cpu_buffer->mapping_lock);
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return err;
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}
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/* prevent another thread from changing buffer/sub-buffer sizes */
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mutex_lock(&buffer->mutex);
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err = rb_alloc_meta_page(cpu_buffer);
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if (err)
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goto unlock;
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/* subbuf_ids include the reader while nr_pages does not */
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subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP_KERNEL);
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if (!subbuf_ids) {
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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
|
||||
|
|
|
|||
Loading…
Reference in a new issue