linux-kernel - [kernel-locking] question about structure field initialization

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Message-ID: <20170511150002.Horde.OdEP2qa_CbPJo1zutiv5Kjn@gator4166.hostgator.com>
Date:   Thu, 11 May 2017 15:00:02 -0500
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     linux-kernel@...r.kernel.org
Subject: [kernel-locking] question about structure field initialization


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?

I'm trying to figure out if this is a false positive or something that  
needs to be fixed.

I'd really appreciate any comment on this.

Thank you!
--
Gustavo A. R. Silva