@@ -72,9 +72,9 @@ For example, if it uses call_rcu(), call_srcu() on srcu_struct_1, and
call_srcu() on srcu_struct_2, then the following three lines of code
will be required when unloading::
- 1 rcu_barrier();
- 2 srcu_barrier(&srcu_struct_1);
- 3 srcu_barrier(&srcu_struct_2);
+ 1 rcu_barrier();
+ 2 srcu_barrier(&srcu_struct_1);
+ 3 srcu_barrier(&srcu_struct_2);
If latency is of the essence, workqueues could be used to run these
three functions concurrently.
@@ -82,69 +82,69 @@ three functions concurrently.
An ancient version of the rcutorture module makes use of rcu_barrier()
in its exit function as follows::
- 1 static void
- 2 rcu_torture_cleanup(void)
- 3 {
- 4 int i;
- 5
- 6 fullstop = 1;
- 7 if (shuffler_task != NULL) {
- 8 VERBOSE_PRINTK_STRING("Stopping rcu_torture_shuffle task");
- 9 kthread_stop(shuffler_task);
- 10 }
- 11 shuffler_task = NULL;
+ 1 static void
+ 2 rcu_torture_cleanup(void)
+ 3 {
+ 4 int i;
+ 5
+ 6 fullstop = 1;
+ 7 if (shuffler_task != NULL) {
+ 8 VERBOSE_PRINTK_STRING("Stopping rcu_torture_shuffle task");
+ 9 kthread_stop(shuffler_task);
+ 10 }
+ 11 shuffler_task = NULL;
12
- 13 if (writer_task != NULL) {
- 14 VERBOSE_PRINTK_STRING("Stopping rcu_torture_writer task");
- 15 kthread_stop(writer_task);
- 16 }
- 17 writer_task = NULL;
+ 13 if (writer_task != NULL) {
+ 14 VERBOSE_PRINTK_STRING("Stopping rcu_torture_writer task");
+ 15 kthread_stop(writer_task);
+ 16 }
+ 17 writer_task = NULL;
18
- 19 if (reader_tasks != NULL) {
- 20 for (i = 0; i < nrealreaders; i++) {
- 21 if (reader_tasks[i] != NULL) {
- 22 VERBOSE_PRINTK_STRING(
- 23 "Stopping rcu_torture_reader task");
- 24 kthread_stop(reader_tasks[i]);
- 25 }
- 26 reader_tasks[i] = NULL;
- 27 }
- 28 kfree(reader_tasks);
- 29 reader_tasks = NULL;
- 30 }
- 31 rcu_torture_current = NULL;
+ 19 if (reader_tasks != NULL) {
+ 20 for (i = 0; i < nrealreaders; i++) {
+ 21 if (reader_tasks[i] != NULL) {
+ 22 VERBOSE_PRINTK_STRING(
+ 23 "Stopping rcu_torture_reader task");
+ 24 kthread_stop(reader_tasks[i]);
+ 25 }
+ 26 reader_tasks[i] = NULL;
+ 27 }
+ 28 kfree(reader_tasks);
+ 29 reader_tasks = NULL;
+ 30 }
+ 31 rcu_torture_current = NULL;
32
- 33 if (fakewriter_tasks != NULL) {
- 34 for (i = 0; i < nfakewriters; i++) {
- 35 if (fakewriter_tasks[i] != NULL) {
- 36 VERBOSE_PRINTK_STRING(
- 37 "Stopping rcu_torture_fakewriter task");
- 38 kthread_stop(fakewriter_tasks[i]);
- 39 }
- 40 fakewriter_tasks[i] = NULL;
- 41 }
- 42 kfree(fakewriter_tasks);
- 43 fakewriter_tasks = NULL;
- 44 }
+ 33 if (fakewriter_tasks != NULL) {
+ 34 for (i = 0; i < nfakewriters; i++) {
+ 35 if (fakewriter_tasks[i] != NULL) {
+ 36 VERBOSE_PRINTK_STRING(
+ 37 "Stopping rcu_torture_fakewriter task");
+ 38 kthread_stop(fakewriter_tasks[i]);
+ 39 }
+ 40 fakewriter_tasks[i] = NULL;
+ 41 }
+ 42 kfree(fakewriter_tasks);
+ 43 fakewriter_tasks = NULL;
+ 44 }
45
- 46 if (stats_task != NULL) {
- 47 VERBOSE_PRINTK_STRING("Stopping rcu_torture_stats task");
- 48 kthread_stop(stats_task);
- 49 }
- 50 stats_task = NULL;
+ 46 if (stats_task != NULL) {
+ 47 VERBOSE_PRINTK_STRING("Stopping rcu_torture_stats task");
+ 48 kthread_stop(stats_task);
+ 49 }
+ 50 stats_task = NULL;
51
- 52 /* Wait for all RCU callbacks to fire. */
- 53 rcu_barrier();
+ 52 /* Wait for all RCU callbacks to fire. */
+ 53 rcu_barrier();
54
- 55 rcu_torture_stats_print(); /* -After- the stats thread is stopped! */
+ 55 rcu_torture_stats_print(); /* -After- the stats thread is stopped! */
56
- 57 if (cur_ops->cleanup != NULL)
- 58 cur_ops->cleanup();
- 59 if (atomic_read(&n_rcu_torture_error))
- 60 rcu_torture_print_module_parms("End of test: FAILURE");
- 61 else
- 62 rcu_torture_print_module_parms("End of test: SUCCESS");
- 63 }
+ 57 if (cur_ops->cleanup != NULL)
+ 58 cur_ops->cleanup();
+ 59 if (atomic_read(&n_rcu_torture_error))
+ 60 rcu_torture_print_module_parms("End of test: FAILURE");
+ 61 else
+ 62 rcu_torture_print_module_parms("End of test: SUCCESS");
+ 63 }
Line 6 sets a global variable that prevents any RCU callbacks from
re-posting themselves. This will not be necessary in most cases, since
@@ -193,16 +193,16 @@ which point, all earlier RCU callbacks are guaranteed to have completed.
The original code for rcu_barrier() was roughly as follows::
- 1 void rcu_barrier(void)
- 2 {
- 3 BUG_ON(in_interrupt());
- 4 /* Take cpucontrol mutex to protect against CPU hotplug */
- 5 mutex_lock(&rcu_barrier_mutex);
- 6 init_completion(&rcu_barrier_completion);
- 7 atomic_set(&rcu_barrier_cpu_count, 1);
- 8 on_each_cpu(rcu_barrier_func, NULL, 0, 1);
- 9 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
- 10 complete(&rcu_barrier_completion);
+ 1 void rcu_barrier(void)
+ 2 {
+ 3 BUG_ON(in_interrupt());
+ 4 /* Take cpucontrol mutex to protect against CPU hotplug */
+ 5 mutex_lock(&rcu_barrier_mutex);
+ 6 init_completion(&rcu_barrier_completion);
+ 7 atomic_set(&rcu_barrier_cpu_count, 1);
+ 8 on_each_cpu(rcu_barrier_func, NULL, 0, 1);
+ 9 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
+ 10 complete(&rcu_barrier_completion);
11 wait_for_completion(&rcu_barrier_completion);
12 mutex_unlock(&rcu_barrier_mutex);
13 }
@@ -232,16 +232,16 @@ still gives the general idea.
The rcu_barrier_func() runs on each CPU, where it invokes call_rcu()
to post an RCU callback, as follows::
- 1 static void rcu_barrier_func(void *notused)
- 2 {
- 3 int cpu = smp_processor_id();
- 4 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
- 5 struct rcu_head *head;
- 6
- 7 head = &rdp->barrier;
- 8 atomic_inc(&rcu_barrier_cpu_count);
- 9 call_rcu(head, rcu_barrier_callback);
- 10 }
+ 1 static void rcu_barrier_func(void *notused)
+ 2 {
+ 3 int cpu = smp_processor_id();
+ 4 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ 5 struct rcu_head *head;
+ 6
+ 7 head = &rdp->barrier;
+ 8 atomic_inc(&rcu_barrier_cpu_count);
+ 9 call_rcu(head, rcu_barrier_callback);
+ 10 }
Lines 3 and 4 locate RCU's internal per-CPU rcu_data structure,
which contains the struct rcu_head that needed for the later call to
@@ -254,11 +254,11 @@ The rcu_barrier_callback() function simply atomically decrements the
rcu_barrier_cpu_count variable and finalizes the completion when it
reaches zero, as follows::
- 1 static void rcu_barrier_callback(struct rcu_head *notused)
- 2 {
- 3 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
- 4 complete(&rcu_barrier_completion);
- 5 }
+ 1 static void rcu_barrier_callback(struct rcu_head *notused)
+ 2 {
+ 3 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
+ 4 complete(&rcu_barrier_completion);
+ 5 }
.. _rcubarrier_quiz_3:
Line numbers in code snippets in rcubarrier.rst have beed left adjusted since commit 4af498306ffd ("doc: Convert to rcubarrier.txt to ReST"). This might have been because right adjusting them had confused Sphinx. The rules around a literal block in reST are: - Need a blank line above it. - A line with the same indent level as the line above it is regarded as the end of it. Those line numbers can be right adjusted by keeping indents at two- digit numbers. While at it, add some spaces between the column of line numbers and the code area for better readability. Signed-off-by: Akira Yokosawa <akiyks@gmail.com> --- Documentation/RCU/rcubarrier.rst | 168 +++++++++++++++---------------- 1 file changed, 84 insertions(+), 84 deletions(-)