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Subject[RFC PATCH v3 2/2] printk-rb: add test module
Date
This module does some heavy write stress testing on the ringbuffer
with a reader that is checking for integrity.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/Makefile | 2 +
kernel/printk/test_prb.c | 256 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 258 insertions(+)
create mode 100644 kernel/printk/test_prb.c

diff --git a/kernel/printk/Makefile b/kernel/printk/Makefile
index 567999aa93af..24365ecee348 100644
--- a/kernel/printk/Makefile
+++ b/kernel/printk/Makefile
@@ -5,3 +5,5 @@ obj-$(CONFIG_PRINTK) += ringbuffer.o
obj-$(CONFIG_PRINTK) += numlist.o
obj-$(CONFIG_PRINTK) += dataring.o
obj-$(CONFIG_A11Y_BRAILLE_CONSOLE) += braille.o
+
+obj-m += test_prb.o
diff --git a/kernel/printk/test_prb.c b/kernel/printk/test_prb.c
new file mode 100644
index 000000000000..1ecb4fcbf823
--- /dev/null
+++ b/kernel/printk/test_prb.c
@@ -0,0 +1,256 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kthread.h>
+#include <linux/delay.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include "ringbuffer.h"
+
+/*
+ * This is a test module that starts "num_online_cpus() - 1" writer threads
+ * and 1 reader thread. The writer threads each write strings of varying
+ * length. They do this as fast as they can.
+ *
+ * The reader thread reads as fast as it can and performs sanity checks on
+ * the data.
+ *
+ * Because the threads are running in such tight loops, they will call
+ * schedule() from time to time so the system stays alive.
+ *
+ * If either the writers or the reader encounter an error, the test is
+ * aborted. Test results are recorded to the ftrace buffers, with some
+ * additional information also provided via printk. The test can be aborted
+ * manually by removing the module. (Ideally the test should never abort on
+ * its own.)
+ */
+
+struct rbdata {
+ int len;
+ char text[0];
+};
+
+static char *test_running;
+static int halt_test;
+
+static void dump_rb(struct printk_ringbuffer *rb)
+{
+ DECLARE_PRINTKRB_ENTRY(entry, 160);
+ DECLARE_PRINTKRB_ITER(iter, rb, &entry);
+ unsigned long last_seq = 0;
+ struct rbdata *dat;
+ char buf[160];
+ int len;
+
+ trace_printk("BEGIN full dump\n");
+
+ prb_for_each_entry_continue(&iter, len) {
+ if (entry.seq - last_seq != 1) {
+ trace_printk("LOST %lu\n",
+ entry.seq - (last_seq + 1));
+ }
+ last_seq = entry.seq;
+
+ dat = (struct rbdata *)&entry.buffer[0];
+
+ snprintf(buf, sizeof(buf), "%s", dat->text);
+ buf[sizeof(buf) - 1] = 0;
+ trace_printk("seq=%lu len=%d textlen=%d dataval=%s\n",
+ entry.seq, len, dat->len, buf);
+ }
+
+ trace_printk("END full dump\n");
+}
+
+DECLARE_PRINTKRB(test_rb, 7, 5);
+
+static int prbtest_writer(void *data)
+{
+ unsigned long num = (unsigned long)data;
+ struct prb_reserved_entry e;
+ char id = 'A' + num;
+ struct rbdata *dat;
+ int count = 0;
+ int len;
+
+ pr_err("prbtest: start thread %lu (writer)\n", num);
+
+ for (;;) {
+ len = sizeof(struct rbdata) + (prandom_u32() & 0x7f) + 2;
+
+ dat = (struct rbdata *)prb_reserve(&e, &test_rb, len);
+ if (!IS_ERR(dat)) {
+ len -= sizeof(struct rbdata) + 1;
+ memset(&dat->text[0], id, len);
+ dat->text[len] = 0;
+ dat->len = len;
+ prb_commit(&e);
+ } else {
+ WRITE_ONCE(halt_test, 1);
+ trace_printk("writer%lu (%c) reserve failed (%ld)\n",
+ num, id, PTR_ERR(dat));
+ }
+
+ if ((count++ & 0x3fff) == 0)
+ schedule();
+
+ if (READ_ONCE(halt_test) == 1)
+ break;
+ }
+
+ pr_err("prbtest: end thread %lu (writer)\n", num);
+
+ test_running[num] = 0;
+
+ return 0;
+}
+
+static int prbtest_reader(void *data)
+{
+ unsigned long num = (unsigned long)data;
+ DECLARE_PRINTKRB_ENTRY(entry, 160);
+ DECLARE_PRINTKRB_ITER(iter, &test_rb, &entry);
+ unsigned long total_lost = 0;
+ unsigned long last_seq = 0;
+ unsigned long max_lost = 0;
+ unsigned long count = 0;
+ struct rbdata *dat;
+ int did_sched = 1;
+ int len;
+
+ pr_err("prbtest: start thread %lu (reader)\n", num);
+
+ for (;;) {
+ prb_for_each_entry_continue(&iter, len) {
+ if (entry.seq < last_seq) {
+ WRITE_ONCE(halt_test, 1);
+ trace_printk(
+ "reader%lu invalid seq %lu -> %lu\n",
+ num, last_seq, entry.seq);
+ goto out;
+ }
+
+ if (entry.seq - last_seq != 1 && !did_sched) {
+ total_lost += entry.seq - (last_seq + 1);
+ if (max_lost < entry.seq - (last_seq + 1))
+ max_lost = entry.seq - (last_seq + 1);
+ }
+ last_seq = entry.seq;
+ did_sched = 0;
+
+ dat = (struct rbdata *)&entry.buffer[0];
+
+ len = strnlen(dat->text, 160);
+ if (len != dat->len || len >= 160) {
+ WRITE_ONCE(halt_test, 1);
+ trace_printk(
+ "reader%lu invalid len for %lu (%d<->%d)\n",
+ num, entry.seq, len, dat->len);
+ goto out;
+ }
+ while (len) {
+ len--;
+ if (dat->text[len] != dat->text[0]) {
+ WRITE_ONCE(halt_test, 1);
+ trace_printk("reader%lu bad data\n",
+ num);
+ goto out;
+ }
+ }
+
+ if ((count++ & 0x3fff) == 0) {
+ did_sched = 1;
+ schedule();
+ }
+
+ if (READ_ONCE(halt_test) == 1)
+ goto out;
+ }
+ if (READ_ONCE(halt_test) == 1)
+ goto out;
+ }
+out:
+ pr_err(
+ "reader%lu: total_lost=%lu max_lost=%lu total_read=%lu seq=%lu\n",
+ num, total_lost, max_lost, count, entry.seq);
+ pr_err("prbtest: end thread %lu (reader)\n", num);
+
+ test_running[num] = 0;
+
+ return 0;
+}
+
+static int module_test_running;
+
+static int start_test(void *arg)
+{
+ struct task_struct *thread;
+ unsigned long i;
+ int num_cpus;
+
+ num_cpus = num_online_cpus();
+ test_running = kzalloc(num_cpus, GFP_KERNEL);
+ if (!test_running)
+ return -ENOMEM;
+
+ module_test_running = 1;
+
+ pr_err("prbtest: starting test\n");
+
+ for (i = 0; i < num_cpus; i++) {
+ test_running[i] = 1;
+ if (i < num_cpus - 1) {
+ thread = kthread_run(prbtest_writer, (void *)i,
+ "prbtest writer");
+ } else {
+ thread = kthread_run(prbtest_reader, (void *)i,
+ "prbtest reader");
+ }
+ if (IS_ERR(thread)) {
+ pr_err("prbtest: unable to create thread %lu\n", i);
+ test_running[i] = 0;
+ }
+ }
+
+ for (;;) {
+ for (i = 0; i < num_cpus; i++) {
+ if (test_running[i] == 1)
+ break;
+ }
+ if (i == num_cpus)
+ break;
+ msleep(1000);
+ }
+
+ pr_err("prbtest: completed test\n");
+
+ dump_rb(&test_rb);
+
+ module_test_running = 0;
+
+ kfree(test_running);
+
+ return 0;
+}
+
+static int prbtest_init(void)
+{
+ kthread_run(start_test, NULL, "prbtest");
+ return 0;
+}
+
+static void prbtest_exit(void)
+{
+ WRITE_ONCE(halt_test, 1);
+
+ while (module_test_running)
+ msleep(1000);
+}
+
+module_init(prbtest_init);
+module_exit(prbtest_exit);
+
+MODULE_AUTHOR("John Ogness <john.ogness@linutronix.de>");
+MODULE_DESCRIPTION("printk ringbuffer test");
+MODULE_LICENSE("GPL v2");
--
2.11.0
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