From patchwork Sun Nov 20 20:07:01 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13050140 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7FA3AC4167E for ; Sun, 20 Nov 2022 20:07:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229779AbiKTUHn (ORCPT ); Sun, 20 Nov 2022 15:07:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52656 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229698AbiKTUHj (ORCPT ); Sun, 20 Nov 2022 15:07:39 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DBBF11CB1B; Sun, 20 Nov 2022 12:07:37 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id B08EBB80B09; Sun, 20 Nov 2022 20:07:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A846C433C1; Sun, 20 Nov 2022 20:07:34 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.96) (envelope-from ) id 1owqbF-00Di3m-1W; Sun, 20 Nov 2022 15:07:33 -0500 Message-ID: <20221120200733.336008061@goodmis.org> User-Agent: quilt/0.66 Date: Sun, 20 Nov 2022 15:07:01 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Andrew Morton , Linux Trace Kernel , Mathieu Desnoyers , Primiano Tucci , stable@vger.kernel.org Subject: [for-linus][PATCH 01/13] tracing/ring-buffer: Have polling block on watermark References: <20221120200700.725968899@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org From: "Steven Rostedt (Google)" Currently the way polling works on the ring buffer is broken. It will return immediately if there's any data in the ring buffer whereas a read will block until the watermark (defined by the tracefs buffer_percent file) is hit. That is, a select() or poll() will return as if there's data available, but then the following read will block. This is broken for the way select()s and poll()s are supposed to work. Have the polling on the ring buffer also block the same way reads and splice does on the ring buffer. Link: https://lkml.kernel.org/r/20221020231427.41be3f26@gandalf.local.home Cc: Linux Trace Kernel Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Primiano Tucci Cc: stable@vger.kernel.org Fixes: 1e0d6714aceb7 ("ring-buffer: Do not wake up a splice waiter when page is not full") Signed-off-by: Steven Rostedt (Google) --- include/linux/ring_buffer.h | 2 +- kernel/trace/ring_buffer.c | 55 ++++++++++++++++++++++++------------- kernel/trace/trace.c | 2 +- 3 files changed, 38 insertions(+), 21 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 2504df9a0453..3c7d295746f6 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -100,7 +100,7 @@ __ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *k int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full); __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu, - struct file *filp, poll_table *poll_table); + struct file *filp, poll_table *poll_table, int full); void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu); #define RING_BUFFER_ALL_CPUS -1 diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9712083832f4..089b1ec9cb3b 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -907,6 +907,21 @@ size_t ring_buffer_nr_dirty_pages(struct trace_buffer *buffer, int cpu) return cnt - read; } +static __always_inline bool full_hit(struct trace_buffer *buffer, int cpu, int full) +{ + struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu]; + size_t nr_pages; + size_t dirty; + + nr_pages = cpu_buffer->nr_pages; + if (!nr_pages || !full) + return true; + + dirty = ring_buffer_nr_dirty_pages(buffer, cpu); + + return (dirty * 100) > (full * nr_pages); +} + /* * rb_wake_up_waiters - wake up tasks waiting for ring buffer input * @@ -1046,22 +1061,20 @@ int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full) !ring_buffer_empty_cpu(buffer, cpu)) { unsigned long flags; bool pagebusy; - size_t nr_pages; - size_t dirty; + bool done; if (!full) break; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page; - nr_pages = cpu_buffer->nr_pages; - dirty = ring_buffer_nr_dirty_pages(buffer, cpu); + done = !pagebusy && full_hit(buffer, cpu, full); + if (!cpu_buffer->shortest_full || cpu_buffer->shortest_full > full) cpu_buffer->shortest_full = full; raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); - if (!pagebusy && - (!nr_pages || (dirty * 100) > full * nr_pages)) + if (done) break; } @@ -1087,6 +1100,7 @@ int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full) * @cpu: the cpu buffer to wait on * @filp: the file descriptor * @poll_table: The poll descriptor + * @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS * * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon * as data is added to any of the @buffer's cpu buffers. Otherwise @@ -1096,14 +1110,15 @@ int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full) * zero otherwise. */ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu, - struct file *filp, poll_table *poll_table) + struct file *filp, poll_table *poll_table, int full) { struct ring_buffer_per_cpu *cpu_buffer; struct rb_irq_work *work; - if (cpu == RING_BUFFER_ALL_CPUS) + if (cpu == RING_BUFFER_ALL_CPUS) { work = &buffer->irq_work; - else { + full = 0; + } else { if (!cpumask_test_cpu(cpu, buffer->cpumask)) return -EINVAL; @@ -1111,8 +1126,14 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu, work = &cpu_buffer->irq_work; } - poll_wait(filp, &work->waiters, poll_table); - work->waiters_pending = true; + if (full) { + poll_wait(filp, &work->full_waiters, poll_table); + work->full_waiters_pending = true; + } else { + poll_wait(filp, &work->waiters, poll_table); + work->waiters_pending = true; + } + /* * There's a tight race between setting the waiters_pending and * checking if the ring buffer is empty. Once the waiters_pending bit @@ -1128,6 +1149,9 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu, */ smp_mb(); + if (full) + return full_hit(buffer, cpu, full) ? EPOLLIN | EPOLLRDNORM : 0; + if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) || (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu))) return EPOLLIN | EPOLLRDNORM; @@ -3155,10 +3179,6 @@ static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer, static __always_inline void rb_wakeups(struct trace_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer) { - size_t nr_pages; - size_t dirty; - size_t full; - if (buffer->irq_work.waiters_pending) { buffer->irq_work.waiters_pending = false; /* irq_work_queue() supplies it's own memory barriers */ @@ -3182,10 +3202,7 @@ rb_wakeups(struct trace_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched); - full = cpu_buffer->shortest_full; - nr_pages = cpu_buffer->nr_pages; - dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu); - if (full && nr_pages && (dirty * 100) <= full * nr_pages) + if (!full_hit(buffer, cpu_buffer->cpu, cpu_buffer->shortest_full)) return; cpu_buffer->irq_work.wakeup_full = true; diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 47a44b055a1d..c6c7a0af3ed2 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6681,7 +6681,7 @@ trace_poll(struct trace_iterator *iter, struct file *filp, poll_table *poll_tabl return EPOLLIN | EPOLLRDNORM; else return ring_buffer_poll_wait(iter->array_buffer->buffer, iter->cpu_file, - filp, poll_table); + filp, poll_table, iter->tr->buffer_percent); } static __poll_t