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Message-Id: <20161201114711.28697-7-chris@chris-wilson.co.uk>
Date: Thu, 1 Dec 2016 11:47:09 +0000
From: Chris Wilson <chris@...is-wilson.co.uk>
To: linux-kernel@...r.kernel.org
Cc: Chris Wilson <chris@...is-wilson.co.uk>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Maarten Lankhorst <dev@...ankhorst.nl>,
Nicolai Hähnle <nhaehnle@...il.com>
Subject: [PATCH v2 6/8] locking: Add kselftests for resolving ww_mutex cyclic deadlocks
Check that ww_mutexes can detect cyclic deadlocks (generalised ABBA
cycles) and resolve them by lock reordering.
Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Maarten Lankhorst <dev@...ankhorst.nl>
Cc: Nicolai Hähnle <nhaehnle@...il.com>
---
kernel/locking/test-ww_mutex.c | 115 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 115 insertions(+)
diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 5a643ba2b020..84da738e57d1 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -21,9 +21,11 @@
#include <linux/completion.h>
#include <linux/kthread.h>
#include <linux/module.h>
+#include <linux/slab.h>
#include <linux/ww_mutex.h>
static DEFINE_WW_CLASS(ww_class);
+struct workqueue_struct *wq;
struct test_mutex {
struct work_struct work;
@@ -243,10 +245,118 @@ static int test_abba(bool resolve)
return ret;
}
+struct test_cycle {
+ struct work_struct work;
+ struct ww_mutex a_mutex;
+ struct ww_mutex *b_mutex;
+ struct completion *a_signal;
+ struct completion b_signal;
+ int result;
+};
+
+static void test_cycle_work(struct work_struct *work)
+{
+ struct test_cycle *cycle = container_of(work, typeof(*cycle), work);
+ struct ww_acquire_ctx ctx;
+ int err;
+
+ ww_acquire_init(&ctx, &ww_class);
+ ww_mutex_lock(&cycle->a_mutex, &ctx);
+
+ complete(cycle->a_signal);
+ wait_for_completion(&cycle->b_signal);
+
+ err = ww_mutex_lock(cycle->b_mutex, &ctx);
+ if (err == -EDEADLK) {
+ ww_mutex_unlock(&cycle->a_mutex);
+ ww_mutex_lock_slow(cycle->b_mutex, &ctx);
+ err = ww_mutex_lock(&cycle->a_mutex, &ctx);
+ }
+
+ if (!err)
+ ww_mutex_unlock(cycle->b_mutex);
+ ww_mutex_unlock(&cycle->a_mutex);
+ ww_acquire_fini(&ctx);
+
+ cycle->result = err;
+}
+
+static int __test_cycle(unsigned int nthreads)
+{
+ struct test_cycle *cycles;
+ unsigned int n, last = nthreads - 1;
+ int ret;
+
+ cycles = kmalloc_array(nthreads, sizeof(*cycles), GFP_KERNEL);
+ if (!cycles)
+ return -ENOMEM;
+
+ for (n = 0; n < nthreads; n++) {
+ struct test_cycle *cycle = &cycles[n];
+
+ ww_mutex_init(&cycle->a_mutex, &ww_class);
+ if (n == last)
+ cycle->b_mutex = &cycles[0].a_mutex;
+ else
+ cycle->b_mutex = &cycles[n + 1].a_mutex;
+
+ if (n == 0)
+ cycle->a_signal = &cycles[last].b_signal;
+ else
+ cycle->a_signal = &cycles[n - 1].b_signal;
+ init_completion(&cycle->b_signal);
+
+ INIT_WORK(&cycle->work, test_cycle_work);
+ cycle->result = 0;
+ }
+
+ for (n = 0; n < nthreads; n++)
+ queue_work(wq, &cycles[n].work);
+
+ flush_workqueue(wq);
+
+ ret = 0;
+ for (n = 0; n < nthreads; n++) {
+ struct test_cycle *cycle = &cycles[n];
+
+ if (!cycle->result)
+ continue;
+
+ pr_err("cylic deadlock not resolved, ret[%d/%d] = %d\n",
+ n, nthreads, cycle->result);
+ ret = -EINVAL;
+ break;
+ }
+
+ for (n = 0; n < nthreads; n++)
+ ww_mutex_destroy(&cycles[n].a_mutex);
+ kfree(cycles);
+ return ret;
+}
+
+static int test_cycle(unsigned int ncpus)
+{
+ unsigned int n;
+ int ret;
+
+ for (n = 2; n <= ncpus + 1; n++) {
+ ret = __test_cycle(n);
+ if (ret)
+ return ret;
+ }
+
+ return 0;
+}
+
static int __init test_ww_mutex_init(void)
{
+ int ncpus = num_online_cpus();
int ret;
+ wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0);
+ if (!wq)
+ return -ENOMEM;
+
ret = test_mutex();
if (ret)
return ret;
@@ -263,11 +373,16 @@ static int __init test_ww_mutex_init(void)
if (ret)
return ret;
+ ret = test_cycle(ncpus);
+ if (ret)
+ return ret;
+
return 0;
}
static void __exit test_ww_mutex_exit(void)
{
+ destroy_workqueue(wq);
}
module_init(test_ww_mutex_init);
--
2.10.2
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