locking/ww_mutex: 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@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Nicolai Hähnle <nhaehnle@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20161201114711.28697-7-chris@chris-wilson.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 5a643ba2b020c2b998c5e2f3890d8ee6434239f6..84da738e57d11f8d2b30e85011f999cd9c5c4b87 100644 (file)
--- 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);