From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756014AbZHMUBa (ORCPT ); Thu, 13 Aug 2009 16:01:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756004AbZHMUBX (ORCPT ); Thu, 13 Aug 2009 16:01:23 -0400 Received: from kroah.org ([198.145.64.141]:41991 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752809AbZHMUAO (ORCPT ); Thu, 13 Aug 2009 16:00:14 -0400 X-Mailbox-Line: From gregkh@mini.kroah.org Thu Aug 13 12:51:35 2009 Message-Id: <20090813195135.112037059@mini.kroah.org> User-Agent: quilt/0.48-1 Date: Thu, 13 Aug 2009 12:50:46 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org, Greg KH Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Robert Richter , Ingo Molnar , Steven Rostedt Subject: [patch 71/74] ring-buffer: Fix advance of reader in rb_buffer_peek() References: <20090813194935.985368088@mini.kroah.org> Content-Disposition: inline; filename=ring-buffer-fix-advance-of-reader-in-rb_buffer_peek.patch In-Reply-To: <20090813195705.GA22393@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.30-stable review patch. If anyone has any objections, please let us know. ------------------ From: Robert Richter Backport for 2.6.30-stable of: 469535a ring-buffer: Fix advance of reader in rb_buffer_peek() When calling rb_buffer_peek() from ring_buffer_consume() and a padding event is returned, the function rb_advance_reader() is called twice. This may lead to missing samples or under high workloads to the warning below. This patch fixes this. If a padding event is returned by rb_buffer_peek() it will be consumed by the calling function now. Also, I simplified some code in ring_buffer_consume(). ------------[ cut here ]------------ WARNING: at /dev/shm/.source/linux/kernel/trace/ring_buffer.c:2289 rb_advance_reader+0x2e/0xc5() Hardware name: Anaheim Modules linked in: Pid: 29, comm: events/2 Tainted: G W 2.6.31-rc3-oprofile-x86_64-standard-00059-g5050dc2 #1 Call Trace: [] ? rb_advance_reader+0x2e/0xc5 [] warn_slowpath_common+0x77/0x8f [] warn_slowpath_null+0xf/0x11 [] rb_advance_reader+0x2e/0xc5 [] ring_buffer_consume+0xa0/0xd2 [] op_cpu_buffer_read_entry+0x21/0x9e [] ? __find_get_block+0x4b/0x165 [] sync_buffer+0xa5/0x401 [] ? __find_get_block+0x4b/0x165 [] ? wq_sync_buffer+0x0/0x78 [] wq_sync_buffer+0x5b/0x78 [] worker_thread+0x113/0x1ac [] ? autoremove_wake_function+0x0/0x38 [] ? worker_thread+0x0/0x1ac [] kthread+0x88/0x92 [] child_rip+0xa/0x20 [] ? kthread+0x0/0x92 [] ? child_rip+0x0/0x20 ---[ end trace f561c0a58fcc89bd ]--- Cc: Steven Rostedt Signed-off-by: Robert Richter Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ring_buffer.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2102,7 +2102,6 @@ rb_buffer_peek(struct ring_buffer *buffe * the box. Return the padding, and we will release * the current locks, and try again. */ - rb_advance_reader(cpu_buffer); return event; case RINGBUF_TYPE_TIME_EXTEND: @@ -2219,6 +2218,8 @@ ring_buffer_peek(struct ring_buffer *buf again: spin_lock_irqsave(&cpu_buffer->reader_lock, flags); event = rb_buffer_peek(buffer, cpu, ts); + if (event && event->type == RINGBUF_TYPE_PADDING) + rb_advance_reader(cpu_buffer); spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); if (event && event->type == RINGBUF_TYPE_PADDING) { @@ -2283,12 +2284,9 @@ ring_buffer_consume(struct ring_buffer * spin_lock_irqsave(&cpu_buffer->reader_lock, flags); event = rb_buffer_peek(buffer, cpu, ts); - if (!event) - goto out_unlock; - - rb_advance_reader(cpu_buffer); + if (event) + rb_advance_reader(cpu_buffer); - out_unlock: spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); out: