[tip:tracing/ftrace] tracing/ftrace: stop {irqs, preempt}soff tracers when tracing is stopped

From: Frederic Weisbecker
Date: Wed Mar 18 2009 - 05:21:18 EST

Commit-ID: 490362003457f8d387f6f6e73e3a7efbf56c3314
Gitweb: http://git.kernel.org/tip/490362003457f8d387f6f6e73e3a7efbf56c3314
Author: Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Tue, 17 Mar 2009 22:38:58 +0100
Commit: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Wed, 18 Mar 2009 10:12:38 +0100

tracing/ftrace: stop {irqs, preempt}soff tracers when tracing is stopped

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@xxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
LKML-Reference: <1237325938-5240-1-git-send-email-fweisbec@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>


---
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();
/* 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 */
--
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