From: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
To: Tyler Retzlaff <roretzla@linux.microsoft.com>
Cc: dev@dpdk.org, thomas@monjalon.net, anatoly.burakov@intel.com,
Narcisa Vasile <navasile@microsoft.com>
Subject: Re: [PATCH v2 2/6] eal: add thread lifetime management
Date: Wed, 22 Jun 2022 01:24:14 +0300 [thread overview]
Message-ID: <20220622012414.09abc32a@sovereign> (raw)
In-Reply-To: <20220621212823.GF18214@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
2022-06-21 14:28 (UTC-0700), Tyler Retzlaff:
> On Tue, Jun 21, 2022 at 10:44:21PM +0300, Dmitry Kozlyuk wrote:
> > 2022-06-21 11:51 (UTC-0700), Tyler Retzlaff:
> > > > > +int
> > > > > +rte_thread_join(rte_thread_t thread_id, unsigned long *value_ptr)
> > > > > +{
> > > > > + int ret = 0;
> > > > > + void *res = NULL;
> > > > > + void **pres = NULL;
> > > > > +
> > > > > + if (value_ptr != NULL)
> > > > > + pres = &res;
> > > > > +
> > > > > + ret = pthread_join((pthread_t)thread_id.opaque_id, pres);
> > > > > + if (ret != 0) {
> > > > > + RTE_LOG(DEBUG, EAL, "pthread_join failed\n");
> > > > > + return ret;
> > > > > + }
> > > > > +
> > > > > + if (value_ptr != NULL && *pres != NULL)
> > > > > + *value_ptr = *(unsigned long *)(*pres);
> > > > > +
> > > > > + return 0;
> > > > > +}
> > > >
> > > > What makes *pres == NULL special?
> > >
> > > it's not clear what you mean, can you explain? maybe there is some
> > > context i am missing from the original patch series?
> >
> > There's no previous context.
> > After ptread_join(), *pres holds the return value of the thread routine.
> > You only assign *value_ptr if value_ptr is not NULL (obviously correct)
> > and if *pres != NULL, that is, if the thread returned a non-NULL value.
> > But this value is opaque, why do you filter NULL?
>
> i don't think it is opaque here? unsigned long * value_ptr says we have
> to store an integer. which leads to a discussion of what should get
> stored at the value_ptr location if pthread_join() itself returns no
> result but the caller of rte_thread_join() requests the result.
There is no question. If `pthread_join()` fails, the function exits early
and `*value_ptr` remains unmodified. If `pthread_join()` succeeds
with a non-NULL second argument (`pres`), `*pres` aka `res` is always filled.
NULL can be placed there too if that's what the thread routine has returned.
>
> > Perhaps you meant if (pres != NULL), no dereference?
>
> that i think is just a repeat of a test checking if the caller of
> rte_thread_join is interested in the result?
> i.e. value_ptr != NULL -> pres != NULL
>
> both pres and *pres are dereferenced so it seems to track that prior to
> those dereferences they have to be validated as being non-NULL.
> i don't see how we could avoid dereferencing **pres to satisfy the
> calling contract when the result is requested.
>
> now if value_ptr was unsigned long ** i guess i'd understand. i could
> always be reading the code wrong. but thinking about further there is
> another problem with this in that we really don't know what is being
> aliased in *pres when using the pthread implementation, since pthread
> could be returning a pointer to something narrow or with unknown layout
> where later dereferencing it as something wider or in this case
> specifically as unsigned long * would have horrible consequences.
Sorry, no, it's just all wrong.
We get a pointer from `pthread_join()` and store it in `res`,
which can also be accessed as `*pres`, because `pres == &res`.
Then we store the lower bits of `res` in an `*value_ptr`.
We don't care what `res` points to because it is never dereferenced.
>
> i think this ends up semi-related to your other comment about what the
> result type from rte_thread_func is, we can discuss offline and post
> details back to the list.
next prev parent reply other threads:[~2022-06-21 22:24 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-09 13:58 [PATCH 0/6] add thread lifetime and attributes API Tyler Retzlaff
2022-06-09 13:58 ` [PATCH 1/6] eal: add thread attributes Tyler Retzlaff
2022-06-09 13:58 ` [PATCH 2/6] eal: add thread lifetime management Tyler Retzlaff
2022-06-09 13:58 ` [PATCH 3/6] eal: add basic rte thread ID equal API Tyler Retzlaff
2022-06-09 22:24 ` Konstantin Ananyev
2022-06-10 22:48 ` Tyler Retzlaff
2022-06-11 12:25 ` Konstantin Ananyev
2022-06-13 13:39 ` Tyler Retzlaff
2022-06-10 0:40 ` fengchengwen
2022-06-09 13:58 ` [PATCH 4/6] test/threads: add tests for thread lifetime API Tyler Retzlaff
2022-06-09 13:58 ` [PATCH 5/6] test/threads: add tests for thread attributes API Tyler Retzlaff
2022-06-09 13:58 ` [PATCH 6/6] test/threads: remove unit test use of pthread Tyler Retzlaff
2022-06-14 23:47 ` [PATCH v2 0/6] add thread lifetime and attributes API Tyler Retzlaff
2022-06-14 23:47 ` [PATCH v2 1/6] eal: add thread attributes Tyler Retzlaff
2022-06-14 23:47 ` [PATCH v2 2/6] eal: add thread lifetime management Tyler Retzlaff
2022-06-18 12:59 ` Dmitry Kozlyuk
2022-06-20 17:39 ` Tyler Retzlaff
2022-06-21 16:24 ` Tyler Retzlaff
2022-06-21 18:51 ` Tyler Retzlaff
2022-06-21 19:44 ` Dmitry Kozlyuk
2022-06-21 21:28 ` Tyler Retzlaff
2022-06-21 22:24 ` Dmitry Kozlyuk [this message]
2022-06-22 18:21 ` Tyler Retzlaff
2022-06-14 23:47 ` [PATCH v2 3/6] eal: add basic rte thread ID equal API Tyler Retzlaff
2022-06-20 8:34 ` Konstantin Ananyev
2022-06-14 23:47 ` [PATCH v2 4/6] test/threads: add tests for thread lifetime API Tyler Retzlaff
2022-06-14 23:47 ` [PATCH v2 5/6] test/threads: add tests for thread attributes API Tyler Retzlaff
2022-06-14 23:47 ` [PATCH v2 6/6] test/threads: remove unit test use of pthread Tyler Retzlaff
2022-06-22 20:26 ` [PATCH v3 0/6] add thread lifetime and attributes API Tyler Retzlaff
2022-06-22 20:26 ` [PATCH v3 1/6] eal: add thread attributes Tyler Retzlaff
2022-06-22 20:26 ` [PATCH v3 2/6] eal: add thread lifetime management Tyler Retzlaff
2022-06-22 20:26 ` [PATCH v3 3/6] eal: add basic rte thread ID equal API Tyler Retzlaff
2022-06-22 20:26 ` [PATCH v3 4/6] test/threads: add tests for thread lifetime API Tyler Retzlaff
2022-06-22 20:26 ` [PATCH v3 5/6] test/threads: add tests for thread attributes API Tyler Retzlaff
2022-06-22 20:26 ` [PATCH v3 6/6] test/threads: remove unit test use of pthread Tyler Retzlaff
2022-06-27 16:56 ` [PATCH v4 0/6] add thread lifetime and attributes API Tyler Retzlaff
2022-06-27 16:56 ` [PATCH v4 1/6] eal: add thread attributes Tyler Retzlaff
2022-06-27 16:56 ` [PATCH v4 2/6] eal: add thread lifetime management Tyler Retzlaff
2022-06-27 16:56 ` [PATCH v4 3/6] eal: add basic rte thread ID equal API Tyler Retzlaff
2022-06-27 16:56 ` [PATCH v4 4/6] test/threads: add tests for thread lifetime API Tyler Retzlaff
2022-06-27 16:56 ` [PATCH v4 5/6] test/threads: add tests for thread attributes API Tyler Retzlaff
2022-06-27 16:56 ` [PATCH v4 6/6] test/threads: remove unit test use of pthread Tyler Retzlaff
2022-07-31 21:16 ` [PATCH v4 0/6] add thread lifetime and attributes API Dmitry Kozlyuk
2022-09-21 8:15 ` David Marchand
2022-09-29 7:02 ` David Marchand
2022-10-05 16:11 ` Tyler Retzlaff
2022-10-05 16:34 ` Tyler Retzlaff
2022-10-06 6:52 ` David Marchand
2022-10-06 15:14 ` Tyler Retzlaff
2022-10-06 13:36 ` Thomas Monjalon
2022-10-06 15:10 ` Tyler Retzlaff
2022-10-06 15:14 ` Thomas Monjalon
2022-10-06 15:20 ` Tyler Retzlaff
2022-10-06 15:26 ` David Marchand
2022-10-06 15:27 ` Tyler Retzlaff
2022-10-05 17:07 ` [PATCH v5 " Tyler Retzlaff
2022-10-05 17:07 ` [PATCH v5 1/6] eal: add thread attributes Tyler Retzlaff
2022-10-06 8:32 ` David Marchand
2022-10-05 17:07 ` [PATCH v5 2/6] eal: add thread lifetime management Tyler Retzlaff
2023-03-01 8:11 ` David Marchand
2023-03-01 20:34 ` Tyler Retzlaff
2022-10-05 17:07 ` [PATCH v5 3/6] eal: add basic rte thread ID equal API Tyler Retzlaff
2022-10-05 17:07 ` [PATCH v5 4/6] test/threads: add tests for thread lifetime API Tyler Retzlaff
2022-10-06 8:32 ` David Marchand
2022-10-06 15:19 ` Tyler Retzlaff
2022-10-05 17:07 ` [PATCH v5 5/6] test/threads: add tests for thread attributes API Tyler Retzlaff
2022-10-05 17:07 ` [PATCH v5 6/6] test/threads: remove unit test use of pthread Tyler Retzlaff
2022-10-06 19:25 ` [PATCH v5 0/6] add thread lifetime and attributes API David Marchand
2022-10-07 19:20 ` Tyler Retzlaff
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