Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755366AbcJLMwP (ORCPT ); Wed, 12 Oct 2016 08:52:15 -0400 Received: from mail.kernel.org ([198.145.29.136]:49380 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755282AbcJLMql (ORCPT ); Wed, 12 Oct 2016 08:46:41 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, "Steven Rostedt (Red Hat)" , Zefan Li Subject: [PATCH 3.4 043/125] ring-buffer: Update read stamp with first real commit on page Date: Wed, 12 Oct 2016 20:32:39 +0800 Message-Id: <1476275641-4697-43-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1476275600-4626-1-git-send-email-lizf@kernel.org> References: <1476275600-4626-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2239 Lines: 65 From: "Steven Rostedt (Red Hat)" 3.4.113-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit b81f472a208d3e2b4392faa6d17037a89442f4ce upstream. Do not update the read stamp after swapping out the reader page from the write buffer. If the reader page is swapped out of the buffer before an event is written to it, then the read_stamp may get an out of date timestamp, as the page timestamp is updated on the first commit to that page. rb_get_reader_page() only returns a page if it has an event on it, otherwise it will return NULL. At that point, check if the page being returned has events and has not been read yet. Then at that point update the read_stamp to match the time stamp of the reader page. Signed-off-by: Steven Rostedt Signed-off-by: Zefan Li --- kernel/trace/ring_buffer.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index bd0f1c4..6cbd36f 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1549,12 +1549,6 @@ rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer) goto again; } -static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer) -{ - cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp; - cpu_buffer->reader_page->read = 0; -} - static void rb_inc_iter(struct ring_buffer_iter *iter) { struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer; @@ -3094,7 +3088,7 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) /* Finally update the reader page to the new head */ cpu_buffer->reader_page = reader; - rb_reset_reader_page(cpu_buffer); + cpu_buffer->reader_page->read = 0; if (overwrite != cpu_buffer->last_overrun) { cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun; @@ -3104,6 +3098,10 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) goto again; out: + /* Update the read_stamp on the first event */ + if (reader && reader->read == 0) + cpu_buffer->read_stamp = reader->page->time_stamp; + arch_spin_unlock(&cpu_buffer->lock); local_irq_restore(flags); -- 1.9.1