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Commit d1b42b80 authored by Chris Wilson's avatar Chris Wilson Committed by Ingo Molnar
Browse files

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: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 70207686

kernel/locking/test-ww_mutex.c

+115 −0
Original line number Diff line number Diff line
@@ -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);