| Message ID | 20240105094729.2363579-2-vdonnefort@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Introducing trace buffer mapping by user-space | expand |
On Fri, 5 Jan 2024 09:47:28 +0000 Vincent Donnefort <vdonnefort@google.com> wrote: > 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() /* 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. > > Signed-off-by: Vincent Donnefort <vdonnefort@google.com> > > diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h > index fa802db216f9..0841ba8bab14 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; > > @@ -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..f950648b0ba9 > --- /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 <linux/types.h> > + > +struct trace_buffer_meta { It is better to add a description about this data structure in kerneldoc style, instead of adding a comment on each field, because this structure will be exposed to user space. > + unsigned long entries; > + unsigned long overrun; > + unsigned long read; > + > + unsigned long subbufs_touched; > + unsigned long subbufs_lost; > + unsigned long subbufs_read; > + > + struct { > + unsigned long lost_events; /* Events lost at the time of the reader swap */ > + __u32 id; /* Reader subbuf ID from 0 to nr_subbufs - 1 */ > + __u32 read; /* Number of bytes read on the reader subbuf */ > + } reader; > + > + __u32 subbuf_size; /* Size of each subbuf including the header */ > + __u32 nr_subbufs; /* Number of subbufs 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 173d2595ce2d..63426e525781 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -338,6 +338,7 @@ 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 */ > }; > > @@ -388,6 +389,7 @@ struct rb_irq_work { > bool waiters_pending; > bool full_waiters_pending; > bool wakeup_full; > + bool is_cpu_buffer; I think 'is_cpu_buffer' is a bit unclear (or generic), what about 'meta_page_update'? > }; > > /* > @@ -484,6 +486,12 @@ 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 *subbuf_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 */ > @@ -739,6 +747,33 @@ 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 rb_irq_work *rbwork) > +{ > + struct ring_buffer_per_cpu *cpu_buffer; > + > + if (!rbwork->is_cpu_buffer) > + return; > + /* > + * If the waiter is a cpu_buffer, this might be due to a > + * userspace mapping. Let's update the meta-page. > + */ > + cpu_buffer = container_of(rbwork, struct ring_buffer_per_cpu, > + irq_work); > + > + 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)); > + WRITE_ONCE(cpu_buffer->meta_page->overrun, > + local_read(&cpu_buffer->overrun)); > + WRITE_ONCE(cpu_buffer->meta_page->subbufs_touched, > + local_read(&cpu_buffer->pages_touched)); > + WRITE_ONCE(cpu_buffer->meta_page->subbufs_lost, > + local_read(&cpu_buffer->pages_lost)); > + } > +} > + > /* > * rb_wake_up_waiters - wake up tasks waiting for ring buffer input > * > @@ -749,6 +784,8 @@ static void rb_wake_up_waiters(struct irq_work *work) > { > struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work); > > + rb_update_meta_page(rbwork); > + > wake_up_all(&rbwork->waiters); > if (rbwork->full_waiters_pending || rbwork->wakeup_full) { > rbwork->wakeup_full = false; > @@ -1541,6 +1578,8 @@ 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); > + cpu_buffer->irq_work.is_cpu_buffer = true; > > bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), > GFP_KERNEL, cpu_to_node(cpu)); > @@ -4544,6 +4583,14 @@ 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->subbufs_read, > + local_read(&cpu_buffer->pages_read)); > + } > + > goto again; > > out: > @@ -4611,6 +4658,12 @@ 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) > @@ -5158,6 +5211,19 @@ 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->subbufs_touched, 0); > + WRITE_ONCE(meta->subbufs_lost, 0); > + WRITE_ONCE(meta->subbufs_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) > { > @@ -5202,6 +5268,9 @@ 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; > } > @@ -5416,6 +5485,11 @@ 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; > @@ -5679,7 +5753,8 @@ 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; > @@ -5898,6 +5973,11 @@ 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); > @@ -5999,6 +6079,308 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) > } > EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set); > > +#define subbuf_page(off, start) \ > + virt_to_page((void *)(start + (off << PAGE_SHIFT))) > + > +#define foreach_subbuf_page(sub_order, start, page) \ > + page = subbuf_page(0, (start)); \ > + for (int __off = 0; __off < (1 << (sub_order)); \ > + __off++, page = subbuf_page(__off, (start))) > + > +static inline void subbuf_map_prepare(unsigned long subbuf_start, int order) > +{ > + struct page *page; > + > + /* > + * When allocating order > 0 pages, only the first struct page has a > + * refcount > 1. Increasing the refcount here ensures none of the struct > + * page composing the sub-buffer is freeed when the mapping is closed. > + */ > + foreach_subbuf_page(order, subbuf_start, page) > + page_ref_inc(page); > +} > + > +static inline void subbuf_unmap(unsigned long subbuf_start, int order) > +{ > + struct page *page; > + > + foreach_subbuf_page(order, subbuf_start, page) { > + page_ref_dec(page); > + page->mapping = NULL; > + } > +} > + > +static void rb_free_subbuf_ids(struct ring_buffer_per_cpu *cpu_buffer) > +{ > + int sub_id; > + > + for (sub_id = 0; sub_id < cpu_buffer->nr_pages + 1; sub_id++) > + subbuf_unmap(cpu_buffer->subbuf_ids[sub_id], > + cpu_buffer->buffer->subbuf_order); > + > + kfree(cpu_buffer->subbuf_ids); > + cpu_buffer->subbuf_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 *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; > + subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order); > + cpu_buffer->reader_page->id = id++; > + > + first_subbuf = subbuf = rb_set_head_page(cpu_buffer); > + do { > + if (id >= nr_subbufs) { > + WARN_ON(1); > + break; > + } > + > + subbuf_ids[id] = (unsigned long)subbuf->page; > + subbuf->id = id; > + subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order); > + > + 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; > + 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, *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) { > + if (cpu_buffer->mapped == INT_MAX) > + err = -EBUSY; > + else > + WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped + 1); > + mutex_unlock(&cpu_buffer->mapping_lock); > + return err; > + } > + > + /* prevent another thread from changing 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 = kzalloc(sizeof(*subbuf_ids) * (cpu_buffer->nr_pages + 1), > + 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); > + /* > + * Ensure rb_update_meta() will observe the meta-page before ^rb_update_meta_page() > + * 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->subbufs_touched, 0, > + local_read(&cpu_buffer->pages_touched)); > + cmpxchg(&cpu_buffer->meta_page->subbufs_lost, 0, > + local_read(&cpu_buffer->pages_lost)); Instead of using these cmpxchg, can we move this initialization before smp_wmb()? Thus we can avoid conflict with rb_update_meta_page() Thank you, > + > + 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_subbuf_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 > + * | subbuffer 0 | > + * +--------------+ pgoff == 1 + (1 << subbuf_order) > + * | subbuffer 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 subbuf_id, subbuf_offset, addr; > + struct page *page; > + > + if (!pgoff) > + return virt_to_page((void *)cpu_buffer->meta_page); > + > + pgoff--; > + > + subbuf_id = pgoff >> buffer->subbuf_order; > + if (subbuf_id > cpu_buffer->nr_pages) > + return NULL; > + > + subbuf_offset = pgoff & ((1UL << buffer->subbuf_order) - 1); > + addr = cpu_buffer->subbuf_ids[subbuf_id] + (subbuf_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 > -- > 2.43.0.472.g3155946c3a-goog >
On Tue, Jan 09, 2024 at 11:42:30PM +0900, Masami Hiramatsu wrote: > On Fri, 5 Jan 2024 09:47:28 +0000 > Vincent Donnefort <vdonnefort@google.com> wrote: > > > 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() /* 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. > > > > Signed-off-by: Vincent Donnefort <vdonnefort@google.com> > > > > diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h > > index fa802db216f9..0841ba8bab14 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; > > > > @@ -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..f950648b0ba9 > > --- /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 <linux/types.h> > > + > > +struct trace_buffer_meta { > > It is better to add a description about this data structure in > kerneldoc style, instead of adding a comment on each field, > because this structure will be exposed to user space. Ack. > > > + unsigned long entries; > > + unsigned long overrun; > > + unsigned long read; > > + > > + unsigned long subbufs_touched; > > + unsigned long subbufs_lost; > > + unsigned long subbufs_read; > > + > > + struct { > > + unsigned long lost_events; /* Events lost at the time of the reader swap */ > > + __u32 id; /* Reader subbuf ID from 0 to nr_subbufs - 1 */ > > + __u32 read; /* Number of bytes read on the reader subbuf */ > > + } reader; > > + > > + __u32 subbuf_size; /* Size of each subbuf including the header */ > > + __u32 nr_subbufs; /* Number of subbufs 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 173d2595ce2d..63426e525781 100644 > > --- a/kernel/trace/ring_buffer.c > > +++ b/kernel/trace/ring_buffer.c > > @@ -338,6 +338,7 @@ 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 */ > > }; > > > > @@ -388,6 +389,7 @@ struct rb_irq_work { > > bool waiters_pending; > > bool full_waiters_pending; > > bool wakeup_full; > > + bool is_cpu_buffer; > > I think 'is_cpu_buffer' is a bit unclear (or generic), > what about 'meta_page_update'? Hum not sure about that change. This was really to identify if parent of rb_irq_work is a cpu_buffer or a trace_buffer. It can be a cpu_buffer regardless of the need to update the meta-page. > > > }; > > > > /* > > @@ -484,6 +486,12 @@ 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 *subbuf_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 */ > > @@ -739,6 +747,33 @@ 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 rb_irq_work *rbwork) > > +{ > > + struct ring_buffer_per_cpu *cpu_buffer; > > + > > + if (!rbwork->is_cpu_buffer) > > + return; > > + /* > > + * If the waiter is a cpu_buffer, this might be due to a > > + * userspace mapping. Let's update the meta-page. > > + */ > > + cpu_buffer = container_of(rbwork, struct ring_buffer_per_cpu, > > + irq_work); > > + > > + 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)); > > + WRITE_ONCE(cpu_buffer->meta_page->overrun, > > + local_read(&cpu_buffer->overrun)); > > + WRITE_ONCE(cpu_buffer->meta_page->subbufs_touched, > > + local_read(&cpu_buffer->pages_touched)); > > + WRITE_ONCE(cpu_buffer->meta_page->subbufs_lost, > > + local_read(&cpu_buffer->pages_lost)); > > + } > > +} > > + > > /* > > * rb_wake_up_waiters - wake up tasks waiting for ring buffer input > > * > > @@ -749,6 +784,8 @@ static void rb_wake_up_waiters(struct irq_work *work) > > { > > struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work); > > > > + rb_update_meta_page(rbwork); > > + > > wake_up_all(&rbwork->waiters); > > if (rbwork->full_waiters_pending || rbwork->wakeup_full) { > > rbwork->wakeup_full = false; > > @@ -1541,6 +1578,8 @@ 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); > > + cpu_buffer->irq_work.is_cpu_buffer = true; > > > > bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), > > GFP_KERNEL, cpu_to_node(cpu)); > > @@ -4544,6 +4583,14 @@ 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->subbufs_read, > > + local_read(&cpu_buffer->pages_read)); > > + } > > + > > goto again; > > > > out: > > @@ -4611,6 +4658,12 @@ 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) > > @@ -5158,6 +5211,19 @@ 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->subbufs_touched, 0); > > + WRITE_ONCE(meta->subbufs_lost, 0); > > + WRITE_ONCE(meta->subbufs_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) > > { > > @@ -5202,6 +5268,9 @@ 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; > > } > > @@ -5416,6 +5485,11 @@ 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; > > @@ -5679,7 +5753,8 @@ 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; > > @@ -5898,6 +5973,11 @@ 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); > > @@ -5999,6 +6079,308 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) > > } > > EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set); > > > > +#define subbuf_page(off, start) \ > > + virt_to_page((void *)(start + (off << PAGE_SHIFT))) > > + > > +#define foreach_subbuf_page(sub_order, start, page) \ > > + page = subbuf_page(0, (start)); \ > > + for (int __off = 0; __off < (1 << (sub_order)); \ > > + __off++, page = subbuf_page(__off, (start))) > > + > > +static inline void subbuf_map_prepare(unsigned long subbuf_start, int order) > > +{ > > + struct page *page; > > + > > + /* > > + * When allocating order > 0 pages, only the first struct page has a > > + * refcount > 1. Increasing the refcount here ensures none of the struct > > + * page composing the sub-buffer is freeed when the mapping is closed. > > + */ > > + foreach_subbuf_page(order, subbuf_start, page) > > + page_ref_inc(page); > > +} > > + > > +static inline void subbuf_unmap(unsigned long subbuf_start, int order) > > +{ > > + struct page *page; > > + > > + foreach_subbuf_page(order, subbuf_start, page) { > > + page_ref_dec(page); > > + page->mapping = NULL; > > + } > > +} > > + > > +static void rb_free_subbuf_ids(struct ring_buffer_per_cpu *cpu_buffer) > > +{ > > + int sub_id; > > + > > + for (sub_id = 0; sub_id < cpu_buffer->nr_pages + 1; sub_id++) > > + subbuf_unmap(cpu_buffer->subbuf_ids[sub_id], > > + cpu_buffer->buffer->subbuf_order); > > + > > + kfree(cpu_buffer->subbuf_ids); > > + cpu_buffer->subbuf_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 *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; > > + subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order); > > + cpu_buffer->reader_page->id = id++; > > + > > + first_subbuf = subbuf = rb_set_head_page(cpu_buffer); > > + do { > > + if (id >= nr_subbufs) { > > + WARN_ON(1); > > + break; > > + } > > + > > + subbuf_ids[id] = (unsigned long)subbuf->page; > > + subbuf->id = id; > > + subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order); > > + > > + 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; > > + 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, *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) { > > + if (cpu_buffer->mapped == INT_MAX) > > + err = -EBUSY; > > + else > > + WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped + 1); > > + mutex_unlock(&cpu_buffer->mapping_lock); > > + return err; > > + } > > + > > + /* prevent another thread from changing 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 = kzalloc(sizeof(*subbuf_ids) * (cpu_buffer->nr_pages + 1), > > + 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); > > + /* > > + * Ensure rb_update_meta() will observe the meta-page before > ^rb_update_meta_page() > > > + * 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->subbufs_touched, 0, > > + local_read(&cpu_buffer->pages_touched)); > > + cmpxchg(&cpu_buffer->meta_page->subbufs_lost, 0, > > + local_read(&cpu_buffer->pages_lost)); > > Instead of using these cmpxchg, can we move this initialization before > smp_wmb()? Thus we can avoid conflict with rb_update_meta_page() Good point, Not sure why I made this more complicated than it should be. > > Thank you, > [...]
On Tue, 9 Jan 2024 15:13:51 +0000 Vincent Donnefort <vdonnefort@google.com> wrote: > > > @@ -388,6 +389,7 @@ struct rb_irq_work { > > > bool waiters_pending; > > > bool full_waiters_pending; > > > bool wakeup_full; > > > + bool is_cpu_buffer; > > > > I think 'is_cpu_buffer' is a bit unclear (or generic), > > what about 'meta_page_update'? > > Hum not sure about that change. This was really to identify if parent of > rb_irq_work is a cpu_buffer or a trace_buffer. It can be a cpu_buffer regardless > of the need to update the meta-page. Yeah, this was added because the irq_work is called with the rb_work for both the cpu_buffer and the global struct tracing_buffer object. The meta_page is only available to the cpu_buffer and does not exist on the struct trace_buffer, so this is checked before doing a "container_of()" on the wrong structure. Both the cpu_buffer and the global buffer call the same function with the rb_work structure. So "is_cpu_buffer" is the right terminology as it's unrelated to the meta page: struct trace_buffer { [..] struct rb_irq_work irq_work; [..] }; struct trace_buffer *buffer; buffer->irq_work.is_cpu_buffer = false; struct ring_buffer_per_cpu { [..] struct rb_irq_work irq_work; [..] } struct ring_buffer_per_cpu *cpu_buffer; cpu_buffer->irq_work.is_cpu_buffer = true; [..] init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters); [..] init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters); // both the buffer and cpu_buffer call rb_wake_up_waiters() static void rb_wake_up_waiters(struct irq_work *work) { struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work); // This container_of() gets rbwork which is the rb_irq_work structure that // both buffer and cpu_buffer have. if (rbwork->is_cpu_buffer) { struct ring_buffer_per_cpu *cpu_buffer; cpu_buffer = container_of(rbwork, struct ring_buffer_per_cpu, irq_work); // The above crashes if done by the buffer and not the cpu_buffer. // The "is_cpu_buffer" is there to differentiate the two rb_work entities. // It is a way to say this is safe to do the above "container_of()". /* * If the waiter is a cpu_buffer, this might be due to a * userspace mapping. Let's update the meta-page. */ rb_update_meta_page(cpu_buffer); } -- Steve
On Tue, 9 Jan 2024 15:13:51 +0000 Vincent Donnefort <vdonnefort@google.com> wrote: > > > @@ -388,6 +389,7 @@ struct rb_irq_work { > > > bool waiters_pending; > > > bool full_waiters_pending; > > > bool wakeup_full; > > > + bool is_cpu_buffer; > > > > I think 'is_cpu_buffer' is a bit unclear (or generic), > > what about 'meta_page_update'? > > Hum not sure about that change. This was really to identify if parent of > rb_irq_work is a cpu_buffer or a trace_buffer. It can be a cpu_buffer regardless > of the need to update the meta-page. Yeah, I just meant that is "for_cpu_buffer", not "rb_irq_work is_cpu_buffer". So when reading the code, I just felt uncomfortable. Thank you,
On Wed, 10 Jan 2024 08:42:05 +0900 Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote: > On Tue, 9 Jan 2024 15:13:51 +0000 > Vincent Donnefort <vdonnefort@google.com> wrote: > > > > > @@ -388,6 +389,7 @@ struct rb_irq_work { > > > > bool waiters_pending; > > > > bool full_waiters_pending; > > > > bool wakeup_full; > > > > + bool is_cpu_buffer; > > > > > > I think 'is_cpu_buffer' is a bit unclear (or generic), > > > what about 'meta_page_update'? > > > > Hum not sure about that change. This was really to identify if parent of > > rb_irq_work is a cpu_buffer or a trace_buffer. It can be a cpu_buffer regardless > > of the need to update the meta-page. > > Yeah, I just meant that is "for_cpu_buffer", not "rb_irq_work is_cpu_buffer". > So when reading the code, I just felt uncomfortable. > How about "in_cpu_buffer" as that is what it is. struct ring_buffer_per_cpu { struct rb_irq_work { bool in_cpu_buffer; } } Would that make you feel more comfortable? ;-) -- Steve
On Tue, Jan 09, 2024 at 06:58:13PM -0500, Steven Rostedt wrote: > On Wed, 10 Jan 2024 08:42:05 +0900 > Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote: > > > On Tue, 9 Jan 2024 15:13:51 +0000 > > Vincent Donnefort <vdonnefort@google.com> wrote: > > > > > > > @@ -388,6 +389,7 @@ struct rb_irq_work { > > > > > bool waiters_pending; > > > > > bool full_waiters_pending; > > > > > bool wakeup_full; > > > > > + bool is_cpu_buffer; > > > > > > > > I think 'is_cpu_buffer' is a bit unclear (or generic), > > > > what about 'meta_page_update'? > > > > > > Hum not sure about that change. This was really to identify if parent of > > > rb_irq_work is a cpu_buffer or a trace_buffer. It can be a cpu_buffer regardless > > > of the need to update the meta-page. > > > > Yeah, I just meant that is "for_cpu_buffer", not "rb_irq_work is_cpu_buffer". > > So when reading the code, I just felt uncomfortable. > > > > How about "in_cpu_buffer" as that is what it is. > > struct ring_buffer_per_cpu { > struct rb_irq_work { > bool in_cpu_buffer; > } > } > > Would that make you feel more comfortable? ;-) > > -- Steve I'll actually solve that by moving that update from the rb_irq_work to ring_buffer_map_get_reader(). Reason is the rb_irq_work is only triggered when !O_NONBLOCK is set. > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >
[...] > > > + */ > > > + 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->subbufs_touched, 0, > > > + local_read(&cpu_buffer->pages_touched)); > > > + cmpxchg(&cpu_buffer->meta_page->subbufs_lost, 0, > > > + local_read(&cpu_buffer->pages_lost)); > > > > Instead of using these cmpxchg, can we move this initialization before > > smp_wmb()? Thus we can avoid conflict with rb_update_meta_page() > > Good point, Not sure why I made this more complicated than it should be. Ha, I know, that was before v6, where the writer was updating all of that. From v6 the update has been moved to the irq_rb_work. > > > > > Thank you, > > > > [...]
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index fa802db216f9..0841ba8bab14 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; @@ -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..f950648b0ba9 --- /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 <linux/types.h> + +struct trace_buffer_meta { + unsigned long entries; + unsigned long overrun; + unsigned long read; + + unsigned long subbufs_touched; + unsigned long subbufs_lost; + unsigned long subbufs_read; + + struct { + unsigned long lost_events; /* Events lost at the time of the reader swap */ + __u32 id; /* Reader subbuf ID from 0 to nr_subbufs - 1 */ + __u32 read; /* Number of bytes read on the reader subbuf */ + } reader; + + __u32 subbuf_size; /* Size of each subbuf including the header */ + __u32 nr_subbufs; /* Number of subbufs 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 173d2595ce2d..63426e525781 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -338,6 +338,7 @@ 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 */ }; @@ -388,6 +389,7 @@ struct rb_irq_work { bool waiters_pending; bool full_waiters_pending; bool wakeup_full; + bool is_cpu_buffer; }; /* @@ -484,6 +486,12 @@ 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 *subbuf_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 */ @@ -739,6 +747,33 @@ 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 rb_irq_work *rbwork) +{ + struct ring_buffer_per_cpu *cpu_buffer; + + if (!rbwork->is_cpu_buffer) + return; + /* + * If the waiter is a cpu_buffer, this might be due to a + * userspace mapping. Let's update the meta-page. + */ + cpu_buffer = container_of(rbwork, struct ring_buffer_per_cpu, + irq_work); + + 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)); + WRITE_ONCE(cpu_buffer->meta_page->overrun, + local_read(&cpu_buffer->overrun)); + WRITE_ONCE(cpu_buffer->meta_page->subbufs_touched, + local_read(&cpu_buffer->pages_touched)); + WRITE_ONCE(cpu_buffer->meta_page->subbufs_lost, + local_read(&cpu_buffer->pages_lost)); + } +} + /* * rb_wake_up_waiters - wake up tasks waiting for ring buffer input * @@ -749,6 +784,8 @@ static void rb_wake_up_waiters(struct irq_work *work) { struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work); + rb_update_meta_page(rbwork); + wake_up_all(&rbwork->waiters); if (rbwork->full_waiters_pending || rbwork->wakeup_full) { rbwork->wakeup_full = false; @@ -1541,6 +1578,8 @@ 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); + cpu_buffer->irq_work.is_cpu_buffer = true; bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), GFP_KERNEL, cpu_to_node(cpu)); @@ -4544,6 +4583,14 @@ 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->subbufs_read, + local_read(&cpu_buffer->pages_read)); + } + goto again; out: @@ -4611,6 +4658,12 @@ 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) @@ -5158,6 +5211,19 @@ 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->subbufs_touched, 0); + WRITE_ONCE(meta->subbufs_lost, 0); + WRITE_ONCE(meta->subbufs_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) { @@ -5202,6 +5268,9 @@ 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; } @@ -5416,6 +5485,11 @@ 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; @@ -5679,7 +5753,8 @@ 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; @@ -5898,6 +5973,11 @@ 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); @@ -5999,6 +6079,308 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) } EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set); +#define subbuf_page(off, start) \ + virt_to_page((void *)(start + (off << PAGE_SHIFT))) + +#define foreach_subbuf_page(sub_order, start, page) \ + page = subbuf_page(0, (start)); \ + for (int __off = 0; __off < (1 << (sub_order)); \ + __off++, page = subbuf_page(__off, (start))) + +static inline void subbuf_map_prepare(unsigned long subbuf_start, int order) +{ + struct page *page; + + /* + * When allocating order > 0 pages, only the first struct page has a + * refcount > 1. Increasing the refcount here ensures none of the struct + * page composing the sub-buffer is freeed when the mapping is closed. + */ + foreach_subbuf_page(order, subbuf_start, page) + page_ref_inc(page); +} + +static inline void subbuf_unmap(unsigned long subbuf_start, int order) +{ + struct page *page; + + foreach_subbuf_page(order, subbuf_start, page) { + page_ref_dec(page); + page->mapping = NULL; + } +} + +static void rb_free_subbuf_ids(struct ring_buffer_per_cpu *cpu_buffer) +{ + int sub_id; + + for (sub_id = 0; sub_id < cpu_buffer->nr_pages + 1; sub_id++) + subbuf_unmap(cpu_buffer->subbuf_ids[sub_id], + cpu_buffer->buffer->subbuf_order); + + kfree(cpu_buffer->subbuf_ids); + cpu_buffer->subbuf_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 *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; + subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order); + cpu_buffer->reader_page->id = id++; + + first_subbuf = subbuf = rb_set_head_page(cpu_buffer); + do { + if (id >= nr_subbufs) { + WARN_ON(1); + break; + } + + subbuf_ids[id] = (unsigned long)subbuf->page; + subbuf->id = id; + subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order); + + 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; + 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, *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) { + if (cpu_buffer->mapped == INT_MAX) + err = -EBUSY; + else + WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped + 1); + mutex_unlock(&cpu_buffer->mapping_lock); + return err; + } + + /* prevent another thread from changing 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 = kzalloc(sizeof(*subbuf_ids) * (cpu_buffer->nr_pages + 1), + 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); + /* + * 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->subbufs_touched, 0, + local_read(&cpu_buffer->pages_touched)); + cmpxchg(&cpu_buffer->meta_page->subbufs_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_subbuf_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 + * | subbuffer 0 | + * +--------------+ pgoff == 1 + (1 << subbuf_order) + * | subbuffer 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 subbuf_id, subbuf_offset, addr; + struct page *page; + + if (!pgoff) + return virt_to_page((void *)cpu_buffer->meta_page); + + pgoff--; + + subbuf_id = pgoff >> buffer->subbuf_order; + if (subbuf_id > cpu_buffer->nr_pages) + return NULL; + + subbuf_offset = pgoff & ((1UL << buffer->subbuf_order) - 1); + addr = cpu_buffer->subbuf_ids[subbuf_id] + (subbuf_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
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() /* 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. Signed-off-by: Vincent Donnefort <vdonnefort@google.com>