Re: [kernel-locking] question about structure field initialization

[Gustavo A. R. Silva]

Hi Chris,

Quoting Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>:

> On Thu, May 11, 2017 at 03:00:02PM -0500, Gustavo A. R. Silva wrote:
> > Hello everybody,
> >
> > While looking into Coverity ID 1402035 I ran into the following
> > piece of code at kernel/locking/test-ww_mutex.c:197:
> >
> > 197static int test_abba(bool resolve)
> > 198{
> > 199        struct test_abba abba;
> > 200        struct ww_acquire_ctx ctx;
> > 201        int err, ret;
> > 202
> > 203        ww_mutex_init(&abba.a_mutex, &ww_class);
> > 204        ww_mutex_init(&abba.b_mutex, &ww_class);
> > 205        INIT_WORK_ONSTACK(&abba.work, test_abba_work);
> > 206        init_completion(&abba.a_ready);
> > 207        init_completion(&abba.b_ready);
> > 208        abba.resolve = resolve;
> > 209
> > 210        schedule_work(&abba.work);
> > 211
> > 212        ww_acquire_init(&ctx, &ww_class);
> > 213        ww_mutex_lock(&abba.a_mutex, &ctx);
> > 214
> > 215        complete(&abba.a_ready);
> > 216        wait_for_completion(&abba.b_ready);
> > 217
> > 218        err = ww_mutex_lock(&abba.b_mutex, &ctx);
> > 219        if (resolve && err == -EDEADLK) {
> > 220                ww_mutex_unlock(&abba.a_mutex);
> > 221                ww_mutex_lock_slow(&abba.b_mutex, &ctx);
> > 222                err = ww_mutex_lock(&abba.a_mutex, &ctx);
> > 223        }
> > 224
> > 225        if (!err)
> > 226                ww_mutex_unlock(&abba.b_mutex);
> > 227        ww_mutex_unlock(&abba.a_mutex);
> > 228        ww_acquire_fini(&ctx);
> > 229
> > 230        flush_work(&abba.work);
> > 231        destroy_work_on_stack(&abba.work);
> > 232
> > 233        ret = 0;
> > 234        if (resolve) {
> > 235                if (err || abba.result) {
> > 236                        pr_err("%s: failed to resolve ABBA
> > deadlock, A err=%d, B err=%d\n",
> > 237                               __func__, err, abba.result);
> > 238                        ret = -EINVAL;
> > 239                }
> > 240        } else {
> > 241                if (err != -EDEADLK && abba.result != -EDEADLK) {
> > 242                        pr_err("%s: missed ABBA deadlock, A
> > err=%d, B err=%d\n",
> > 243                               __func__, err, abba.result);
> > 244                        ret = -EINVAL;
> > 245                }
> > 246        }
> > 247        return ret;
> > 248}
> >
> > The issue here is that apparently abba.result is being used at lines
> > 235, 237 and 241 without previous initialization.
> >
> > It seems to me that this is an issue, but I may be overlooking something.
> > Can someone help me to spot where exactly abba.result is being
> > initialized, if at all?
>
> You are only looking at half the code. Though the schedule/flush it is
> indirectly executing test_abba_work().
> -Chris

I get it.

Thanks for clarifying!
--
Gustavo A. R. Silva