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Message-ID: <20090317214926.GA5137@nowhere>
Date: Tue, 17 Mar 2009 22:49:27 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/ftrace: stop {irqs,preempt}soff tracers when
tracing is stopped
On Tue, Mar 17, 2009 at 05:46:14PM -0400, Steven Rostedt wrote:
>
>
>
> On Tue, 17 Mar 2009, Frederic Weisbecker wrote:
>
> > Impact: fix a selftest warning
> >
> > In some cases, it's possible to see the following warning on irqsoff
> > tracer selftest:
> >
> > [ 4.640003] Testing tracer irqsoff: <4>------------[ cut here ]------------
> > [ 4.653562] WARNING: at kernel/trace/trace.c:458 update_max_tr_single+0x9a/0xc4()
> > [ 4.660000] Hardware name: System Product Name
> > [ 4.660000] Modules linked in:
> > [ 4.660000] Pid: 301, comm: kstop/1 Not tainted 2.6.29-rc8-tip #35837
> > [ 4.660000] Call Trace:
> > [ 4.660000] [<4014b588>] warn_slowpath+0x79/0x8f
> > [ 4.660000] [<402d6949>] ? put_dec+0x64/0x6b
> > [ 4.660000] [<40162b56>] ? getnstimeofday+0x58/0xdd
> > [ 4.660000] [<40162210>] ? clocksource_read+0x3/0xf
> > [ 4.660000] [<4015eb44>] ? ktime_set+0x8/0x34
> > [ 4.660000] [<4014101a>] ? balance_runtime+0x8/0x56
> > [ 4.660000] [<405f6f11>] ? _spin_lock+0x3/0x10
> > [ 4.660000] [<4011f643>] ? ftrace_call+0x5/0x8
> > [ 4.660000] [<4015d0f1>] ? task_cputime_zero+0x3/0x27
> > [ 4.660000] [<40190ee7>] ? cpupri_set+0x90/0xcb
> > [ 4.660000] [<405f7208>] ? _spin_lock_irqsave+0x22/0x34
> > [ 4.660000] [<40190f12>] ? cpupri_set+0xbb/0xcb
> > [ 4.660000] [<405f7151>] ? _spin_unlock_irqrestore+0x23/0x35
> > [ 4.660000] [<4018493f>] ? ring_buffer_reset_cpu+0x27/0x51
> > [ 4.660000] [<405f7208>] ? _spin_lock_irqsave+0x22/0x34
> > [ 4.660000] [<40184962>] ? ring_buffer_reset_cpu+0x4a/0x51
> > [ 4.660000] [<405f7151>] ? _spin_unlock_irqrestore+0x23/0x35
> > [ 4.660000] [<4018cc29>] ? trace_hardirqs_off+0x1a/0x1c
> > [ 4.660000] [<405f7151>] ? _spin_unlock_irqrestore+0x23/0x35
> > [ 4.660000] [<40184962>] ? ring_buffer_reset_cpu+0x4a/0x51
> > [ 4.660000] [<401850f3>] ? cpumask_next+0x15/0x18
> > [ 4.660000] [<4018a41f>] update_max_tr_single+0x9a/0xc4
> > [ 4.660000] [<4014e5fe>] ? exit_notify+0x16/0xf2
> > [ 4.660000] [<4018cd13>] check_critical_timing+0xcc/0x11e
> > [ 4.660000] [<4014e5fe>] ? exit_notify+0x16/0xf2
> > [ 4.660000] [<4014e5fe>] ? exit_notify+0x16/0xf2
> > [ 4.660000] [<4018cdf1>] stop_critical_timing+0x8c/0x9f
> > [ 4.660000] [<4014e5c4>] ? forget_original_parent+0xac/0xd0
> > [ 4.660000] [<4018ce3a>] trace_hardirqs_on+0x1a/0x1c
> > [ 4.660000] [<4014e5c4>] forget_original_parent+0xac/0xd0
> > [ 4.660000] [<4014e5fe>] exit_notify+0x16/0xf2
> > [ 4.660000] [<4014e8a5>] do_exit+0x1cb/0x225
> > [ 4.660000] [<4015c72b>] ? kthread+0x0/0x69
> > [ 4.660000] [<4011f61d>] kernel_thread_helper+0xd/0x10
> > [ 4.660000] ---[ end trace a7919e7f17c0a725 ]---
> > [ 4.660164] .. no entries found ..FAILED!
> >
> > During the selftest of irqsoff tracer, we do that:
> >
> > /* disable interrupts for a bit */
> > local_irq_disable();
> > udelay(100);
> > local_irq_enable();
> > /* stop the tracing. */
> > tracing_stop();
> > /* check both trace buffers */
> > ret = trace_test_buffer(tr, NULL);
> >
> > If a callsite performs a new max delay with irqs off just after
> > tracing_stop, update_max_tr_single() -> ring_buffer_swap_cpu()
> > will be called with the buffers disabled by tracing_stop(), hence
> > the warning, then ring_buffer_swap_cpu() return -EAGAIN and
> > update_max_tr_single() complains.
> >
> > Fix it by also stopping the tracer before stopping the tracing globally.
> > A similar situation can happen with preemptoff and preemptirqsoff tracers
> > where we apply the same fix.
> >
> > Reported-by: Ingo Molnar <mingo@...e.hu>
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > ---
> > kernel/trace/trace_selftest.c | 26 ++++++++++++++++++++++++++
> > 1 files changed, 26 insertions(+), 0 deletions(-)
> >
> > diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
> > index a2ca6f0..38856ba 100644
> > --- a/kernel/trace/trace_selftest.c
> > +++ b/kernel/trace/trace_selftest.c
> > @@ -315,6 +315,14 @@ trace_selftest_startup_irqsoff(struct tracer *trace, struct trace_array *tr)
> > local_irq_disable();
> > udelay(100);
> > local_irq_enable();
> > +
> > + /*
> > + * Stop the tracer to avoid a warning subsequent
> > + * to buffer flipping failure because tracing_stop()
> > + * disables the tr and max buffers, making flipping impossible
> > + * in case of parallels max irqs off latencies.
> > + */
> > + trace->stop(tr);
> > /* stop the tracing. */
> > tracing_stop();
> > /* check both trace buffers */
> > @@ -369,6 +377,14 @@ trace_selftest_startup_preemptoff(struct tracer *trace, struct trace_array *tr)
> > preempt_disable();
> > udelay(100);
> > preempt_enable();
> > +
> > + /*
> > + * Stop the tracer to avoid a warning subsequent
> > + * to buffer flipping failure because tracing_stop()
> > + * disables the tr and max buffers, making flipping impossible
> > + * in case of parallels max preempt off latencies.
> > + */
> > + trace->stop(tr);
> > /* stop the tracing. */
> > tracing_stop();
>
> I'm actually thinking that tracing_stop() should call the current tracer
> "stop" function.
>
> -- Steve
Indeed, it could be better.
But I think of a combination of stop() callback call plus
ring buffer disabled because I'm not sure all tracers implement
the stop callback.
Should I send a v2 based on the above?
> > /* check both trace buffers */
> > @@ -428,6 +444,13 @@ trace_selftest_startup_preemptirqsoff(struct tracer *trace, struct trace_array *
> > /* reverse the order of preempt vs irqs */
> > local_irq_enable();
> >
> > + /*
> > + * Stop the tracer to avoid a warning subsequent
> > + * to buffer flipping failure because tracing_stop()
> > + * disables the tr and max buffers, making flipping impossible
> > + * in case of parallels max irqs/preempt off latencies.
> > + */
> > + trace->stop(tr);
> > /* stop the tracing. */
> > tracing_stop();
> > /* check both trace buffers */
> > @@ -448,6 +471,8 @@ trace_selftest_startup_preemptirqsoff(struct tracer *trace, struct trace_array *
> > /* do the test by disabling interrupts first this time */
> > tracing_max_latency = 0;
> > tracing_start();
> > + trace->start(tr);
> > +
> > preempt_disable();
> > local_irq_disable();
> > udelay(100);
> > @@ -455,6 +480,7 @@ trace_selftest_startup_preemptirqsoff(struct tracer *trace, struct trace_array *
> > /* reverse the order of preempt vs irqs */
> > local_irq_enable();
> >
> > + trace->stop(tr);
> > /* stop the tracing. */
> > tracing_stop();
> > /* check both trace buffers */
> > --
> > 1.6.1
> >
> >
--
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