Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Fri, 28 Jul 2023 17:47:53 +0100 | Subject | [PATCH v5 1/2] ring-buffer: Introducing ring-buffer mapping functions | From | Vincent Donnefort <> |
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In preparation for allowing the user-space to map a ring-buffer, add a set of mapping functions:
ring_buffer_{map,unmap}() ring_buffer_map_fault()
And controls on the ring-buffer:
ring_buffer_map_get_reader_page() /* swap reader and head */
Mapping the ring-buffer also involves:
A unique ID for each page of the ring-buffer, as currently the pages are only identified through their in-kernel VA.
A meta-page, where are stored statistics about the ring-buffer and a page IDs list, ordered. A field gives what page is the reader one and one to gives where the ring-buffer starts in the list of data pages.
The linear mapping exposes the meta-page, and each page of the ring-buffer, ordered following their unique ID, assigned during the first mapping.
Once mapped, no page 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 pages.
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 782e14f62201..980abfbd92ed 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 +213,9 @@ 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_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..653176cc50bc --- /dev/null +++ b/include/uapi/linux/trace_mmap.h @@ -0,0 +1,26 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_TRACE_MMAP_H_ +#define _UAPI_TRACE_MMAP_H_ + +#include <linux/types.h> + +struct ring_buffer_meta { + unsigned long entries; + unsigned long overrun; + unsigned long read; + + unsigned long pages_touched; + unsigned long pages_lost; + unsigned long pages_read; + + __u32 meta_page_size; + __u32 nr_data_pages; /* Number of pages in the ring-buffer */ + + struct reader_page { + __u32 id; /* Reader page ID from 0 to nr_data_pages - 1 */ + __u32 read; /* Number of bytes read on the reader page */ + unsigned long lost_events; /* Events lost at the time of the reader swap */ + } reader_page; +}; + +#endif /* _UAPI_TRACE_MMAP_H_ */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index de061dd47313..8f367fd3dbdd 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 */ }; /* @@ -523,6 +524,12 @@ 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 *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 */ @@ -1562,6 +1569,13 @@ 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 void rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer, @@ -1725,6 +1739,7 @@ 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)); @@ -2521,6 +2536,15 @@ 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)); + WRITE_ONCE(cpu_buffer->meta_page->pages_lost, + local_read(&cpu_buffer->pages_lost)); + } + /* * The entries will be zeroed out when we move the * tail page. @@ -3183,6 +3207,14 @@ 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); } @@ -3486,7 +3518,7 @@ 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; @@ -4658,6 +4690,13 @@ 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_page.read, 0); + WRITE_ONCE(cpu_buffer->meta_page->reader_page.id, reader->id); + WRITE_ONCE(cpu_buffer->meta_page->reader_page.lost_events, cpu_buffer->lost_events); + WRITE_ONCE(cpu_buffer->meta_page->pages_read, local_read(&cpu_buffer->pages_read)); + } + goto again; out: @@ -4724,6 +4763,13 @@ static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer) length = rb_event_length(event); cpu_buffer->reader_page->read += length; + + if (cpu_buffer->mapped) { + WRITE_ONCE(cpu_buffer->meta_page->reader_page.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) @@ -5253,6 +5299,19 @@ 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 ring_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->pages_touched, 0); + WRITE_ONCE(meta->pages_lost, 0); + WRITE_ONCE(meta->pages_read, local_read(&cpu_buffer->pages_read)); + WRITE_ONCE(meta->reader_page.read, cpu_buffer->reader_page->read); +} + static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) { @@ -5297,6 +5356,9 @@ 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); } @@ -5511,6 +5573,11 @@ 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; @@ -5753,7 +5820,8 @@ 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; @@ -5870,6 +5938,255 @@ int ring_buffer_read_page(struct trace_buffer *buffer, } EXPORT_SYMBOL_GPL(ring_buffer_read_page); +static void rb_free_page_ids(struct ring_buffer_per_cpu *cpu_buffer) +{ + int i; + + for (i = 0; i < cpu_buffer->nr_pages + 1; i++) + virt_to_page(cpu_buffer->page_ids[i])->mapping = NULL; + + 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; + + 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(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 *page_ids) +{ + struct ring_buffer_meta *meta = cpu_buffer->meta_page; + unsigned int nr_data_pages = cpu_buffer->nr_pages + 1; + 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 >= nr_data_pages) { + WARN_ON(1); + break; + } + + page_ids[id] = (unsigned long)bpage->page; + bpage->id = id; + + rb_inc_page(&bpage); + id++; + } while (bpage != first_page); + + /* install page ID to kern VA translation */ + cpu_buffer->page_ids = page_ids; + + meta->meta_page_size = PAGE_SIZE; + meta->nr_data_pages = nr_data_pages; + meta->reader_page.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, *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)); + cmpxchg(&cpu_buffer->meta_page->pages_lost, 0, + local_read(&cpu_buffer->pages_lost)); + + 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 | page_ids=0 + * +--------------+ + * | data page2 | 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((void *)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_map_get_reader_page(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long reader_size, 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); + 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 -- 2.41.0.487.g6d72f3e995-goog
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