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locking/ww_mutex: Add kselftests for resolving ww_mutex cyclic deadlocks
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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>
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Chris Wilson authored and Ingo Molnar committed Jan 14, 2017
1 parent 7020768 commit d1b42b8
Showing 1 changed file with 115 additions and 0 deletions.
115 changes: 115 additions & 0 deletions kernel/locking/test-ww_mutex.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand All @@ -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);
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