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Message-ID: <20150904093856.GI22739@pathway.suse.cz>
Date: Fri, 4 Sep 2015 11:38:56 +0200
From: Petr Mladek <pmladek@...e.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Josh Triplett <josh@...htriplett.org>,
Thomas Gleixner <tglx@...utronix.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
Vlastimil Babka <vbabka@...e.cz>,
live-patching@...r.kernel.org, linux-api@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 10/14] ring_buffer: Fix more races when terminating
the producer in the benchmark
On Mon 2015-08-03 14:33:23, Steven Rostedt wrote:
> On Tue, 28 Jul 2015 16:39:27 +0200
> Petr Mladek <pmladek@...e.com> wrote:
>
> > @@ -384,7 +389,7 @@ static int ring_buffer_consumer_thread(void *arg)
> >
> > static int ring_buffer_producer_thread(void *arg)
> > {
> > - while (!kthread_should_stop() && !kill_test) {
> > + while (!break_test()) {
> > ring_buffer_reset(buffer);
> >
> > if (consumer) {
> > @@ -393,11 +398,15 @@ static int ring_buffer_producer_thread(void *arg)
> > }
> >
> > ring_buffer_producer();
> > - if (kill_test)
> > + if (break_test())
> > goto out_kill;
> >
> > trace_printk("Sleeping for 10 secs\n");
> > set_current_state(TASK_INTERRUPTIBLE);
> > + if (break_test()) {
> > + __set_current_state(TASK_RUNNING);
>
> Move the setting of the current state to after the out_kill label.
Please, find below the updated version of this patch.
I also reverted some changes in the consumer code. It never stays
in a loop for too long and it must stay in ring_buffer_producer()
until "reader_finish" variable is set.
>From 7f5b1a5b8cf8248245897b55ffc51a6d74c8e15b Mon Sep 17 00:00:00 2001
From: Petr Mladek <pmladek@...e.com>
Date: Fri, 19 Jun 2015 14:38:36 +0200
Subject: [PATCH 2/2] ring_buffer: Fix more races when terminating the producer
in the benchmark
The commit b44754d8262d3aab8 ("ring_buffer: Allow to exit the ring
buffer benchmark immediately") added a hack into ring_buffer_producer()
that set @kill_test when kthread_should_stop() returned true. It improved
the situation a lot. It stopped the kthread in most cases because
the producer spent most of the time in the patched while cycle.
But there are still few possible races when kthread_should_stop()
is set outside of the cycle. Then we do not set @kill_test and
some other checks pass.
This patch adds a better fix. It renames @test_kill/TEST_KILL() into
a better descriptive @test_error/TEST_ERROR(). Also it introduces
break_test() function that checks for both @test_error and
kthread_should_stop().
The new function is used in the producer when the check for @test_error
is not enough. It is not used in the consumer because its state
is manipulated by the producer via the "reader_finish" variable.
Also we add a missing check into ring_buffer_producer_thread()
between setting TASK_INTERRUPTIBLE and calling schedule_timeout().
Otherwise, we might miss a wakeup from kthread_stop().
Signed-off-by: Petr Mladek <pmladek@...e.com>
---
kernel/trace/ring_buffer_benchmark.c | 54 +++++++++++++++++++-----------------
1 file changed, 29 insertions(+), 25 deletions(-)
diff --git a/kernel/trace/ring_buffer_benchmark.c b/kernel/trace/ring_buffer_benchmark.c
index 045e0a24c2a0..d1bfe4399e96 100644
--- a/kernel/trace/ring_buffer_benchmark.c
+++ b/kernel/trace/ring_buffer_benchmark.c
@@ -60,12 +60,12 @@ MODULE_PARM_DESC(consumer_fifo, "fifo prio for consumer");
static int read_events;
-static int kill_test;
+static int test_error;
-#define KILL_TEST() \
+#define TEST_ERROR() \
do { \
- if (!kill_test) { \
- kill_test = 1; \
+ if (!test_error) { \
+ test_error = 1; \
WARN_ON(1); \
} \
} while (0)
@@ -75,6 +75,11 @@ enum event_status {
EVENT_DROPPED,
};
+static bool break_test(void)
+{
+ return test_error || kthread_should_stop();
+}
+
static enum event_status read_event(int cpu)
{
struct ring_buffer_event *event;
@@ -87,7 +92,7 @@ static enum event_status read_event(int cpu)
entry = ring_buffer_event_data(event);
if (*entry != cpu) {
- KILL_TEST();
+ TEST_ERROR();
return EVENT_DROPPED;
}
@@ -115,10 +120,10 @@ static enum event_status read_page(int cpu)
rpage = bpage;
/* The commit may have missed event flags set, clear them */
commit = local_read(&rpage->commit) & 0xfffff;
- for (i = 0; i < commit && !kill_test; i += inc) {
+ for (i = 0; i < commit && !test_error ; i += inc) {
if (i >= (PAGE_SIZE - offsetof(struct rb_page, data))) {
- KILL_TEST();
+ TEST_ERROR();
break;
}
@@ -128,7 +133,7 @@ static enum event_status read_page(int cpu)
case RINGBUF_TYPE_PADDING:
/* failed writes may be discarded events */
if (!event->time_delta)
- KILL_TEST();
+ TEST_ERROR();
inc = event->array[0] + 4;
break;
case RINGBUF_TYPE_TIME_EXTEND:
@@ -137,12 +142,12 @@ static enum event_status read_page(int cpu)
case 0:
entry = ring_buffer_event_data(event);
if (*entry != cpu) {
- KILL_TEST();
+ TEST_ERROR();
break;
}
read++;
if (!event->array[0]) {
- KILL_TEST();
+ TEST_ERROR();
break;
}
inc = event->array[0] + 4;
@@ -150,17 +155,17 @@ static enum event_status read_page(int cpu)
default:
entry = ring_buffer_event_data(event);
if (*entry != cpu) {
- KILL_TEST();
+ TEST_ERROR();
break;
}
read++;
inc = ((event->type_len + 1) * 4);
}
- if (kill_test)
+ if (test_error)
break;
if (inc <= 0) {
- KILL_TEST();
+ TEST_ERROR();
break;
}
}
@@ -185,7 +190,7 @@ static void ring_buffer_consumer(void)
while (!READ_ONCE(reader_finish)) {
int found = 1;
- while (found && !kill_test) {
+ while (found && !test_error) {
int cpu;
found = 0;
@@ -197,7 +202,7 @@ static void ring_buffer_consumer(void)
else
stat = read_page(cpu);
- if (kill_test)
+ if (test_error)
break;
if (stat == EVENT_FOUND)
@@ -279,10 +284,7 @@ static void ring_buffer_producer(void)
if (cnt % wakeup_interval)
cond_resched();
#endif
- if (kthread_should_stop())
- kill_test = 1;
-
- } while (ktime_before(end_time, timeout) && !kill_test);
+ } while (ktime_before(end_time, timeout) && !break_test());
trace_printk("End ring buffer hammer\n");
if (consumer) {
@@ -303,7 +305,7 @@ static void ring_buffer_producer(void)
entries = ring_buffer_entries(buffer);
overruns = ring_buffer_overruns(buffer);
- if (kill_test && !kthread_should_stop())
+ if (test_error)
trace_printk("ERROR!\n");
if (!disable_reader) {
@@ -384,15 +386,14 @@ static void wait_to_die(void)
static int ring_buffer_consumer_thread(void *arg)
{
- while (!kthread_should_stop() && !kill_test) {
+ while (!break_test()) {
complete(&read_start);
ring_buffer_consumer();
set_current_state(TASK_INTERRUPTIBLE);
- if (kthread_should_stop() || kill_test)
+ if (break_test())
break;
-
schedule();
}
__set_current_state(TASK_RUNNING);
@@ -405,7 +406,7 @@ static int ring_buffer_consumer_thread(void *arg)
static int ring_buffer_producer_thread(void *arg)
{
- while (!kthread_should_stop() && !kill_test) {
+ while (!break_test()) {
ring_buffer_reset(buffer);
if (consumer) {
@@ -414,15 +415,18 @@ static int ring_buffer_producer_thread(void *arg)
}
ring_buffer_producer();
- if (kill_test)
+ if (break_test())
goto out_kill;
trace_printk("Sleeping for 10 secs\n");
set_current_state(TASK_INTERRUPTIBLE);
+ if (break_test())
+ goto out_kill;
schedule_timeout(HZ * SLEEP_TIME);
}
out_kill:
+ __set_current_state(TASK_RUNNING);
if (!kthread_should_stop())
wait_to_die();
--
1.8.5.6
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