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().

Link: http://lkml.kernel.org/r/1441629518-32712-3-git-send-email-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer_benchmark.c b/kernel/trace/ring_buffer_benchmark.c
index 9ea7949366b3a90e274766830a21f8e4857341f9..9e00fd17822657428f4ef71715ac8332acf9ee6a 100644 (file)
--- 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)
@@ -273,10 +278,7 @@ 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) {
@@ -297,7 +299,7 @@ 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) {
@@ -378,15 +380,14 @@ 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);
@@ -399,7 +400,7 @@ 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) {
@@ -408,15 +409,18 @@ 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();