The codebase scatters hardcoded minimum page limits across multiple places. Introduce RING_BUFFER_MIN_NR_PAGES and rb_calculate_nr_pages() to formalize the requirement of two pages in a ring buffer.
Signed-off-by: Vincent Donnefort <[email protected]> --- include/linux/ring_buffer.h | 9 ++++++++- kernel/trace/ring_buffer.c | 32 +++++++++++++------------------ kernel/trace/simple_ring_buffer.c | 4 ++-- 3 files changed, 23 insertions(+), 22 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index eac3e9080c3c..e4370064273e 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -98,6 +98,13 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size); +/* + * A minimum of 2 pages ensures we can always swap a page out of the ring + * buffer. This does not account for the reader page or any other page + * containing meta data used by static ring buffers. + */ +#define RING_BUFFER_MIN_NR_PAGES 2UL + /* * Because the ring buffer is generic, if other users of the ring buffer get * traced by ftrace, it can produce lockdep warnings. We need to keep each @@ -287,7 +294,7 @@ static inline struct ring_buffer_desc *__first_ring_buffer_desc(struct trace_buf static inline unsigned long __calc_nr_pages_ring_buffer_desc(size_t size) { /* Takes into account the reader page */ - return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; + return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), RING_BUFFER_MIN_NR_PAGES) + 1; } static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned int nr_cpus) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9c03a555a6ba..7137781ab0b8 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -642,6 +642,11 @@ static __always_inline unsigned int rb_subbuf_max_data_size(struct trace_buffer return rb_subbuf_capacity(buffer) - RB_EVNT_HDR_SIZE - sizeof(event->array[0]); } +static unsigned long rb_calculate_nr_pages(struct trace_buffer *buffer, unsigned long size) +{ + return max(DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)), RING_BUFFER_MIN_NR_PAGES); +} + /** * rb_subbuf_start - Get the start address of a subbuffer * @buffer: A trace buffer @@ -2865,7 +2870,7 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, goto fail_free_buffers; /* Need at least two pages plus the reader page */ - if (nr_pages < 3) + if (nr_pages < RING_BUFFER_MIN_NR_PAGES + 1) goto fail_free_buffers; again: @@ -2877,7 +2882,7 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, ptr += subbuf_size * nr_pages; } if (ptr > end) { - if (nr_pages <= 3) + if (nr_pages <= RING_BUFFER_MIN_NR_PAGES + 1) goto fail_free_buffers; nr_pages--; goto again; @@ -2900,13 +2905,10 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, if (nr_pages > rb_static_max_pages()) goto fail_free_buffers; - if (nr_pages < 2) + if (nr_pages < RING_BUFFER_MIN_NR_PAGES) goto fail_free_buffers; } else { - /* need at least two pages */ - nr_pages = DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)); - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_calculate_nr_pages(buffer, size); } cpumask_set_cpu(cpu, buffer->cpumask); @@ -3319,11 +3321,7 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size, mutex_lock(&buffer->mutex); atomic_inc(&buffer->resizing); - nr_pages = DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)); - - /* we need a minimum of two pages */ - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_calculate_nr_pages(buffer, size); if (cpu_id == RING_BUFFER_ALL_CPUS) { /* @@ -7495,12 +7493,8 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) } /* Update the number of pages to match the new size */ - nr_pages = old_capacity * buffer->buffers[cpu]->nr_pages; - nr_pages = DIV_ROUND_UP(nr_pages, rb_subbuf_capacity(buffer)); - - /* we need a minimum of two pages */ - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_calculate_nr_pages(buffer, + old_capacity * buffer->buffers[cpu]->nr_pages); cpu_buffer->nr_pages_to_update = nr_pages; @@ -8095,7 +8089,7 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node) } /* allocate minimum pages, user can later expand it */ if (!nr_pages_same) - nr_pages = 2; + nr_pages = RING_BUFFER_MIN_NR_PAGES; buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu); if (!buffer->buffers[cpu]) { diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c index 49913bb0057a..abfaf9bee12e 100644 --- a/kernel/trace/simple_ring_buffer.c +++ b/kernel/trace/simple_ring_buffer.c @@ -383,8 +383,8 @@ int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer, void *page; int i; - /* At least 1 reader page and two pages in the ring-buffer */ - if (desc->nr_page_va < 3) + /* At least RING_BUFFER_MIN_NR_PAGES and 1 reader page */ + if (desc->nr_page_va < RING_BUFFER_MIN_NR_PAGES + 1) return -EINVAL; memset(cpu_buffer, 0, sizeof(*cpu_buffer)); -- 2.55.0.1007.g17ff1f9808-goog
