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Message-Id: <1438094371-8326-11-git-send-email-pmladek@suse.com>
Date: Tue, 28 Jul 2015 16:39:27 +0200
From: Petr Mladek <pmladek@...e.com>
To: 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>
Cc: Steven Rostedt <rostedt@...dmis.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, Petr Mladek <pmladek@...e.com>
Subject: [RFC PATCH 10/14] 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(). Finally, the new function is used
on many locations when the check for @test_error is not enough.
Also it adds 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().
Finally, it adds the same check also into ring_buffer_consumer()
between setting TASK_INTERRUPTIBLE and calling schedule_timeout().
Well, I added this one just for paranoid reasons. If we are here
the producer should have been destroyed before and it should have
set @reader_finish. But better be safe.
Signed-off-by: Petr Mladek <pmladek@...e.com>
---
kernel/trace/ring_buffer_benchmark.c | 65 ++++++++++++++++++++----------------
1 file changed, 37 insertions(+), 28 deletions(-)
diff --git a/kernel/trace/ring_buffer_benchmark.c b/kernel/trace/ring_buffer_benchmark.c
index ccb1a0b95f64..10e0ec9b797f 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 +120,13 @@ 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 ; i += inc) {
+
+ if (break_test())
+ break;
if (i >= (PAGE_SIZE - offsetof(struct rb_page, data))) {
- KILL_TEST();
+ TEST_ERROR();
break;
}
@@ -128,7 +136,7 @@ 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 +145,12 @@ 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 +158,17 @@ 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;
}
}
@@ -178,7 +186,7 @@ static void ring_buffer_consumer(void)
read_events ^= 1;
read = 0;
- while (!reader_finish && !kill_test) {
+ while (!reader_finish && !break_test()) {
int found;
do {
@@ -193,17 +201,18 @@ static void ring_buffer_consumer(void)
else
stat = read_page(cpu);
- if (kill_test)
+ if (break_test())
break;
if (stat == EVENT_FOUND)
found = 1;
}
- } while (found && !kill_test);
+ } while (found && !break_test());
set_current_state(TASK_INTERRUPTIBLE);
- if (reader_finish)
+ if (reader_finish || break_test()) {
+ __set_current_state(TASK_RUNNING);
break;
-
+ }
schedule();
}
reader_finish = 0;
@@ -263,10 +272,7 @@ 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) {
@@ -282,7 +288,7 @@ 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) {
@@ -363,15 +369,14 @@ 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);
@@ -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);
+ goto out_kill;
+ }
schedule_timeout(HZ * SLEEP_TIME);
}
--
1.8.5.6
--
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