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>
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@ -21,9 +21,11 @@
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#include <linux/completion.h>
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#include <linux/kthread.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/ww_mutex.h>
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static DEFINE_WW_CLASS(ww_class);
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struct workqueue_struct *wq;
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struct test_mutex {
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struct work_struct work;
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@ -243,10 +245,118 @@ static int test_abba(bool resolve)
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return ret;
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}
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struct test_cycle {
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struct work_struct work;
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struct ww_mutex a_mutex;
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struct ww_mutex *b_mutex;
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struct completion *a_signal;
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struct completion b_signal;
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int result;
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};
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static void test_cycle_work(struct work_struct *work)
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{
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struct test_cycle *cycle = container_of(work, typeof(*cycle), work);
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struct ww_acquire_ctx ctx;
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int err;
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ww_acquire_init(&ctx, &ww_class);
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ww_mutex_lock(&cycle->a_mutex, &ctx);
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complete(cycle->a_signal);
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wait_for_completion(&cycle->b_signal);
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err = ww_mutex_lock(cycle->b_mutex, &ctx);
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if (err == -EDEADLK) {
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ww_mutex_unlock(&cycle->a_mutex);
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ww_mutex_lock_slow(cycle->b_mutex, &ctx);
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err = ww_mutex_lock(&cycle->a_mutex, &ctx);
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}
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if (!err)
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ww_mutex_unlock(cycle->b_mutex);
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ww_mutex_unlock(&cycle->a_mutex);
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ww_acquire_fini(&ctx);
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cycle->result = err;
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}
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static int __test_cycle(unsigned int nthreads)
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{
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struct test_cycle *cycles;
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unsigned int n, last = nthreads - 1;
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int ret;
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cycles = kmalloc_array(nthreads, sizeof(*cycles), GFP_KERNEL);
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if (!cycles)
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return -ENOMEM;
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for (n = 0; n < nthreads; n++) {
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struct test_cycle *cycle = &cycles[n];
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ww_mutex_init(&cycle->a_mutex, &ww_class);
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if (n == last)
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cycle->b_mutex = &cycles[0].a_mutex;
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else
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cycle->b_mutex = &cycles[n + 1].a_mutex;
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if (n == 0)
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cycle->a_signal = &cycles[last].b_signal;
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else
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cycle->a_signal = &cycles[n - 1].b_signal;
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init_completion(&cycle->b_signal);
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INIT_WORK(&cycle->work, test_cycle_work);
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cycle->result = 0;
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}
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for (n = 0; n < nthreads; n++)
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queue_work(wq, &cycles[n].work);
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flush_workqueue(wq);
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ret = 0;
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for (n = 0; n < nthreads; n++) {
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struct test_cycle *cycle = &cycles[n];
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if (!cycle->result)
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continue;
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pr_err("cylic deadlock not resolved, ret[%d/%d] = %d\n",
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n, nthreads, cycle->result);
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ret = -EINVAL;
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break;
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}
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for (n = 0; n < nthreads; n++)
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ww_mutex_destroy(&cycles[n].a_mutex);
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kfree(cycles);
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return ret;
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}
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static int test_cycle(unsigned int ncpus)
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{
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unsigned int n;
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int ret;
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for (n = 2; n <= ncpus + 1; n++) {
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ret = __test_cycle(n);
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if (ret)
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return ret;
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}
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return 0;
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}
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static int __init test_ww_mutex_init(void)
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{
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int ncpus = num_online_cpus();
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int ret;
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wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0);
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if (!wq)
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return -ENOMEM;
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ret = test_mutex();
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if (ret)
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return ret;
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@ -263,11 +373,16 @@ static int __init test_ww_mutex_init(void)
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if (ret)
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return ret;
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ret = test_cycle(ncpus);
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if (ret)
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return ret;
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return 0;
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}
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static void __exit test_ww_mutex_exit(void)
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{
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destroy_workqueue(wq);
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}
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module_init(test_ww_mutex_init);
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