[dpdk-dev] [PATCH v5] eal: fix race in ctrl thread creation
Honnappa Nagarahalli
Honnappa.Nagarahalli at arm.com
Wed Apr 7 17:15:53 CEST 2021
<snip>
>
> Hi Luc,
>
> On Wed, Apr 07, 2021 at 08:53:23AM -0400, Luc Pelletier wrote:
> > The creation of control threads uses a pthread barrier for
> > synchronization. This patch fixes a race condition where the pthread
> > barrier could get destroyed while one of the threads has not yet
> > returned from the pthread_barrier_wait function, which could result in
> > undefined behaviour.
> >
> > Fixes: 3a0d465d4c53 ("eal: fix use-after-free on control thread
> > creation")
> > Cc: jianfeng.tan at intel.com
> > Cc: stable at dpdk.org
> >
> > Signed-off-by: Luc Pelletier <lucp.at.work at gmail.com>
> > ---
> >
> > Same as v4 except that I fixed 2 minor style issues flagged by patchwork.
> >
> > lib/librte_eal/common/eal_common_thread.c | 52
> > +++++++++++------------
> > 1 file changed, 25 insertions(+), 27 deletions(-)
> >
> > diff --git a/lib/librte_eal/common/eal_common_thread.c
> > b/lib/librte_eal/common/eal_common_thread.c
> > index 73a055902..c1044e795 100644
> > --- a/lib/librte_eal/common/eal_common_thread.c
> > +++ b/lib/librte_eal/common/eal_common_thread.c
> > @@ -170,11 +170,19 @@ struct rte_thread_ctrl_params {
> > void *(*start_routine)(void *);
> > void *arg;
> > pthread_barrier_t configured;
> > + unsigned int refcnt;
> > };
> >
> > +static void ctrl_params_free(struct rte_thread_ctrl_params *params) {
> > + if (__atomic_sub_fetch(¶ms->refcnt, 1, __ATOMIC_ACQ_REL) ==
> 0) {
> > + pthread_barrier_destroy(¶ms->configured);
> > + free(params);
> > + }
> > +}
> > +
> > static void *ctrl_thread_init(void *arg) {
> > - int ret;
> > struct internal_config *internal_conf =
> > eal_get_internal_configuration();
> > rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset; @@ -184,11
> > +192,8 @@ static void *ctrl_thread_init(void *arg)
> >
> > __rte_thread_init(rte_lcore_id(), cpuset);
> >
> > - ret = pthread_barrier_wait(¶ms->configured);
> > - if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
> > - pthread_barrier_destroy(¶ms->configured);
> > - free(params);
> > - }
> > + pthread_barrier_wait(¶ms->configured);
> > + ctrl_params_free(params);
> >
> > return start_routine(routine_arg);
> > }
> > @@ -210,14 +215,15 @@ rte_ctrl_thread_create(pthread_t *thread, const
> > char *name,
> >
> > params->start_routine = start_routine;
> > params->arg = arg;
> > + params->refcnt = 2;
> >
> > - pthread_barrier_init(¶ms->configured, NULL, 2);
> > + ret = pthread_barrier_init(¶ms->configured, NULL, 2);
> > + if (ret != 0)
> > + goto fail_no_barrier;
> >
> > ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
> > - if (ret != 0) {
> > - free(params);
> > - return -ret;
> > - }
> > + if (ret != 0)
> > + goto fail_with_barrier;
> >
> > if (name != NULL) {
> > ret = rte_thread_setname(*thread, name); @@ -227,25
> +233,17 @@
> > rte_ctrl_thread_create(pthread_t *thread, const char *name,
> > }
> >
> > ret = pthread_setaffinity_np(*thread, sizeof(*cpuset), cpuset);
> > - if (ret)
> > - goto fail;
> > + pthread_barrier_wait(¶ms->configured);
> > + ctrl_params_free(params);
> >
> > - ret = pthread_barrier_wait(¶ms->configured);
> > - if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
> > - pthread_barrier_destroy(¶ms->configured);
> > - free(params);
> > - }
> > + return -ret;
>
> I think not killing the thread when pthread_setaffinity_np() returns an error is
> not very understandable from the API user point of view.
Agree.
>
> What about doing this on top of your patch? The idea is to set start_routine
> to NULL before the barrier if pthread_setaffinity_np() failed. So there is no
> need to cancel the thread, it will exit by itself.
How about using the pthread_attr_setaffinity_np API?
It is deviating from the documentation of the 'rte_ctrl_thread_create'. But, from the user perspective, the behavior should not change.
This way we do not have to handle the error after the thread is launched.
>
> @@ -187,14 +187,18 @@ static void *ctrl_thread_init(void *arg)
> eal_get_internal_configuration();
> rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset;
> struct rte_thread_ctrl_params *params = arg;
> - void *(*start_routine)(void *) = params->start_routine;
> + void *(*start_routine)(void *);
> void *routine_arg = params->arg;
>
> __rte_thread_init(rte_lcore_id(), cpuset);
>
> pthread_barrier_wait(¶ms->configured);
> + start_routine = params->start_routine;
> ctrl_params_free(params);
>
> + if (start_routine == NULL)
> + return NULL;
> +
> return start_routine(routine_arg);
> }
>
> @@ -233,10 +237,18 @@ rte_ctrl_thread_create(pthread_t *thread, const
> char *name,
> }
>
> ret = pthread_setaffinity_np(*thread, sizeof(*cpuset), cpuset);
> + if (ret != 0)
> + params->start_routine = NULL;
> +
> pthread_barrier_wait(¶ms->configured);
> ctrl_params_free(params);
>
> - return -ret;
> + if (ret != 0) {
> + pthread_join(*thread, NULL);
> + return -ret;
> + }
> +
> + return 0;
>
> fail_with_barrier:
> pthread_barrier_destroy(¶ms->configured);
>
>
> Regards,
> Olivier
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