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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 bpage of the ring-buffer, ordered following their unique ID, assigned during the first mapping. Once mapped, no bpage 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 the buffer pages. Signed-off-by: Vincent Donnefort diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 929ed54dd651..e77a2685fe52 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; @@ -221,4 +223,9 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node); #define trace_rb_cpu_prepare NULL #endif +int ring_buffer_map(struct trace_buffer *buffer, int cpu); +int ring_buffer_unmap(struct trace_buffer *buffer, int cpu); +struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu, + unsigned long pgoff); +int ring_buffer_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..9536f0b7c094 --- /dev/null +++ b/include/uapi/linux/trace_mmap.h @@ -0,0 +1,29 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_TRACE_MMAP_H_ +#define _UAPI_TRACE_MMAP_H_ + +#include + +struct trace_buffer_meta { + unsigned long entries; + unsigned long overrun; + unsigned long read; + + unsigned long bpages_touched; + unsigned long bpages_lost; + unsigned long bpages_read; + + struct { + unsigned long lost_events; /* Events lost at the time of the reader swap */ + __u32 id; /* Reader bpage ID from 0 to nr_bpages - 1 */ + __u32 read; /* Number of bytes read on the reader bpage */ + } reader; + + __u32 bpage_size; /* Size of each buffer page including the header */ + __u32 nr_bpages; /* Number of buffer pages in the ring-buffer */ + + __u32 meta_page_size; /* Size of the meta-page */ + __u32 meta_struct_len; /* Len of this struct */ +}; + +#endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index f95ad0f5be1b..2a6307af9c6c 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -335,6 +335,7 @@ struct buffer_page { local_t write; /* index for next write */ unsigned read; /* index for next read */ local_t entries; /* entries on this page */ + u32 id; /* ID for external mapping */ unsigned long real_end; /* real end of data */ unsigned order; /* order of the page */ struct buffer_data_page *page; /* Actual data page */ @@ -483,6 +484,12 @@ 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 *bpage_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 */ @@ -760,6 +767,22 @@ static __always_inline bool full_hit(struct trace_buffer *buffer, int cpu, int f return (dirty * 100) > (full * nr_pages); } +static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + if (unlikely(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)); + WRITE_ONCE(cpu_buffer->meta_page->overrun, + local_read(&cpu_buffer->overrun)); + WRITE_ONCE(cpu_buffer->meta_page->bpages_touched, + local_read(&cpu_buffer->pages_touched)); + WRITE_ONCE(cpu_buffer->meta_page->bpages_lost, + local_read(&cpu_buffer->pages_lost)); + } +} + /* * rb_wake_up_waiters - wake up tasks waiting for ring buffer input * @@ -769,6 +792,10 @@ static __always_inline bool full_hit(struct trace_buffer *buffer, int cpu, int f static void rb_wake_up_waiters(struct irq_work *work) { struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work); + struct ring_buffer_per_cpu *cpu_buffer = + container_of(rbwork, struct ring_buffer_per_cpu, irq_work); + + rb_update_meta_page(cpu_buffer); wake_up_all(&rbwork->waiters); if (rbwork->full_waiters_pending || rbwork->wakeup_full) { @@ -1562,6 +1589,7 @@ 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)); @@ -4474,6 +4502,14 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->last_overrun = overwrite; } + if (cpu_buffer->mapped) { + WRITE_ONCE(cpu_buffer->meta_page->reader.read, 0); + WRITE_ONCE(cpu_buffer->meta_page->reader.id, reader->id); + WRITE_ONCE(cpu_buffer->meta_page->reader.lost_events, cpu_buffer->lost_events); + WRITE_ONCE(cpu_buffer->meta_page->bpages_read, + local_read(&cpu_buffer->pages_read)); + } + goto again; out: @@ -4541,6 +4577,12 @@ static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer) length = rb_event_length(event); cpu_buffer->reader_page->read += length; cpu_buffer->read_bytes += length; + if (cpu_buffer->mapped) { + WRITE_ONCE(cpu_buffer->meta_page->reader.read, + cpu_buffer->reader_page->read); + WRITE_ONCE(cpu_buffer->meta_page->read, + cpu_buffer->read); + } } static void rb_advance_iter(struct ring_buffer_iter *iter) @@ -5088,6 +5130,19 @@ static void rb_clear_buffer_page(struct buffer_page *page) page->read = 0; } +static void rb_reset_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct trace_buffer_meta *meta = cpu_buffer->meta_page; + + WRITE_ONCE(meta->entries, 0); + WRITE_ONCE(meta->overrun, 0); + WRITE_ONCE(meta->read, cpu_buffer->read); + WRITE_ONCE(meta->bpages_touched, 0); + WRITE_ONCE(meta->bpages_lost, 0); + WRITE_ONCE(meta->bpages_read, local_read(&cpu_buffer->pages_read)); + WRITE_ONCE(meta->reader.read, cpu_buffer->reader_page->read); +} + static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) { @@ -5132,6 +5187,9 @@ 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_reset_meta_page(cpu_buffer); + rb_head_page_activate(cpu_buffer); cpu_buffer->pages_removed = 0; } @@ -5346,6 +5404,11 @@ 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; @@ -5609,7 +5672,8 @@ 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; @@ -5828,6 +5892,11 @@ int ring_buffer_page_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->bpage_size); @@ -5929,6 +5998,308 @@ int ring_buffer_page_order_set(struct trace_buffer *buffer, int order) } EXPORT_SYMBOL_GPL(ring_buffer_page_order_set); +#define bpage_subpage(sub_off, start) \ + virt_to_page((void *)(start + (sub_off << PAGE_SHIFT))) + +#define foreach_bpage_subpage(sub_off, bpage_order, start, page) \ + for (sub_off = 0, page = bpage_subpage(0, start); \ + sub_off < (1 << bpage_order); \ + sub_off++, page = bpage_subpage(sub_off, start)) + +static inline void bpage_map_prepare(unsigned long start, int order) +{ + struct page *page; + int subpage_off; + + /* + * When allocating order > 0 pages, only the first struct page has a + * refcount > 1. Increasing the refcount here ensures the none of the + * struct page composing the bpage is freeed when the mapping is closed. + */ + foreach_bpage_subpage(subpage_off, order, start, page) + page_ref_inc(page); +} + +static inline void bpage_unmap(unsigned long start, int order) +{ + struct page *page; + int subpage_off; + + foreach_bpage_subpage(subpage_off, order, start, page) { + page_ref_dec(page); + page->mapping = NULL; + } +} + +static void rb_free_bpage_ids(struct ring_buffer_per_cpu *cpu_buffer) +{ + int sub_id; + + for (sub_id = 0; sub_id < cpu_buffer->nr_pages + 1; sub_id++) + bpage_unmap(cpu_buffer->bpage_ids[sub_id], + cpu_buffer->buffer->bpage_order); + + kfree(cpu_buffer->bpage_ids); + cpu_buffer->bpage_ids = NULL; +} + +static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + if (cpu_buffer->meta_page) + return 0; + + cpu_buffer->meta_page = page_to_virt(alloc_page(GFP_USER)); + if (!cpu_buffer->meta_page) + return -ENOMEM; + + return 0; +} + +static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + unsigned long addr = (unsigned long)cpu_buffer->meta_page; + + virt_to_page((void *)addr)->mapping = NULL; + free_page(addr); + cpu_buffer->meta_page = NULL; +} + +static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, + unsigned long *bpage_ids) +{ + struct trace_buffer_meta *meta = cpu_buffer->meta_page; + unsigned int nr_bpages = cpu_buffer->nr_pages + 1; + struct buffer_page *first_page, *bpage; + int id = 0; + + bpage_ids[id] = (unsigned long)cpu_buffer->reader_page->page; + bpage_map_prepare(bpage_ids[id], cpu_buffer->buffer->bpage_order); + cpu_buffer->reader_page->id = id++; + + first_page = bpage = rb_set_head_page(cpu_buffer); + do { + + if (id >= nr_bpages) { + WARN_ON(1); + break; + } + + bpage_ids[id] = (unsigned long)bpage->page; + bpage->id = id; + bpage_map_prepare(bpage_ids[id], cpu_buffer->buffer->bpage_order); + + rb_inc_page(&bpage); + id++; + } while (bpage != first_page); + + /* install page ID to kern VA translation */ + cpu_buffer->bpage_ids = bpage_ids; + + meta->meta_page_size = PAGE_SIZE; + meta->meta_struct_len = sizeof(*meta); + meta->nr_bpages = nr_bpages; + meta->bpage_size = cpu_buffer->buffer->bpage_size + BUF_PAGE_HDR_SIZE; + meta->reader.id = cpu_buffer->reader_page->id; + rb_reset_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 = 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, *bpage_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); + + err = rb_alloc_meta_page(cpu_buffer); + if (err) + goto unlock; + + /* bpage_ids include the reader while nr_pages does not */ + bpage_ids = kzalloc(sizeof(*bpage_ids) * (cpu_buffer->nr_pages + 1), + GFP_KERNEL); + if (!bpage_ids) { + rb_free_meta_page(cpu_buffer); + err = -ENOMEM; + goto unlock; + } + + atomic_inc(&cpu_buffer->resize_disabled); + + /* + * 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, bpage_ids); + /* + * Ensure rb_update_meta() 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->bpages_touched, 0, + local_read(&cpu_buffer->pages_touched)); + cmpxchg(&cpu_buffer->meta_page->bpages_lost, 0, + local_read(&cpu_buffer->pages_lost)); + + 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 = 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 for the writer and readers to observe !mapped */ + synchronize_rcu(); + + rb_free_bpage_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 == 0 + * | meta page | + * +--------------+ pgoff == 1 + * | bpage 0 | + * +--------------+ pgoff == 1 + (1 << bpage_order) + * | bpage 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]; + unsigned long bpage_id, bpage_offset, addr; + struct page *page; + + if (!pgoff) + return virt_to_page((void *)cpu_buffer->meta_page); + + pgoff--; + + bpage_id = pgoff >> buffer->bpage_order; + if (bpage_id > cpu_buffer->nr_pages) + return NULL; + + bpage_offset = pgoff & ((1UL << buffer->bpage_order) - 1); + addr = cpu_buffer->bpage_ids[bpage_id] + (bpage_offset * PAGE_SIZE); + page = 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 = 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: + 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