[dpdk-stable] [dpdk-dev] [PATCH v2] eal: fix race in ctrl thread creation
Honnappa Nagarahalli
Honnappa.Nagarahalli at arm.com
Fri Apr 2 06:34:52 CEST 2021
<snip>
>
> As reported by Luc, there is a race where the barrier is destroyed by one
> thread, while the other thread did not yet leave pthread_barrier_wait.
Please correct me if I am wrong. We are using the pthread_barrier to
1) know when to free 'params'.
2) set the thread affinity before the thread starts running its function
I think this patch is fine. But, it can be simplified.
>
> This patch fixes the race condition by adding an atomic counter to ensure
> that the barrier is destroyed only it is not used by any thread.
>
> Fixes: 3a0d465d4c53 ("eal: fix use-after-free on control thread creation")
> Cc: jianfeng.tan at intel.com
> Cc: stable at dpdk.org
>
> Reported-by: Luc Pelletier <lucp.at.work at gmail.com>
> Signed-off-by: David Marchand <david.marchand at redhat.com>
> Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>
> ---
>
> Hi Luc,
>
> Thank you for reporting this problem and submitting the patch.
> I think the issue can be fixed without any loop, like in this patch. What do
> you think?
>
> Regards,
> Olivier
>
>
> lib/librte_eal/common/eal_common_thread.c | 38 +++++++++++++----------
> 1 file changed, 21 insertions(+), 17 deletions(-)
>
> diff --git a/lib/librte_eal/common/eal_common_thread.c
> b/lib/librte_eal/common/eal_common_thread.c
> index 73a055902a..891f825e87 100644
> --- a/lib/librte_eal/common/eal_common_thread.c
> +++ b/lib/librte_eal/common/eal_common_thread.c
> @@ -170,11 +170,11 @@ struct rte_thread_ctrl_params {
> void *(*start_routine)(void *);
> void *arg;
> pthread_barrier_t configured;
We can get rid of the barrier variable. The 'barrier_refcnt' is enough to know when to free the memory.
Setting the thread affinity can be moved to 'ctrl_thread_init' function.
> + unsigned int barrier_refcnt;
> };
>
> 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; @@ -184,8
> +184,9 @@ 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_wait(¶ms->configured);
> + if (__atomic_sub_fetch(¶ms->barrier_refcnt, 1,
> + __ATOMIC_ACQ_REL) == 0) {
> pthread_barrier_destroy(¶ms->configured);
> free(params);
> }
> @@ -210,15 +211,17 @@ rte_ctrl_thread_create(pthread_t *thread, const
> char *name,
>
> params->start_routine = start_routine;
> params->arg = arg;
> -
> - pthread_barrier_init(¶ms->configured, NULL, 2);
> -
> - ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
> + __atomic_store_n(¶ms->barrier_refcnt, 2,
> __ATOMIC_RELEASE);
We can use __ATOMIC_RELAXED or just a simple assignment as pthread_create ensures that all the earlier memory writes are visible to the 'ctrl_thread_init'.
> + ret = pthread_barrier_init(¶ms->configured, NULL, 2);
> if (ret != 0) {
> free(params);
> return -ret;
> }
>
> + ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
> + if (ret != 0)
> + goto fail;
> +
> if (name != NULL) {
> ret = rte_thread_setname(*thread, name);
> if (ret < 0)
> @@ -227,25 +230,26 @@ rte_ctrl_thread_create(pthread_t *thread, const
> char *name,
> }
>
> ret = pthread_setaffinity_np(*thread, sizeof(*cpuset), cpuset);
I think this can be moved to 'ctrl_thread_init'.
> - if (ret)
> - goto fail;
> + if (ret != 0)
> + goto fail_cancel;
>
> - ret = pthread_barrier_wait(¶ms->configured);
> - if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
> + pthread_barrier_wait(¶ms->configured);
> + if (__atomic_sub_fetch(¶ms->barrier_refcnt, 1,
> + __ATOMIC_ACQ_REL) == 0) {
> pthread_barrier_destroy(¶ms->configured);
> free(params);
> }
>
> return 0;
>
> -fail:
> - if (PTHREAD_BARRIER_SERIAL_THREAD ==
> - pthread_barrier_wait(¶ms->configured)) {
> - pthread_barrier_destroy(¶ms->configured);
> - free(params);
> - }
> +fail_cancel:
> pthread_cancel(*thread);
> pthread_join(*thread, NULL);
> +
> +fail:
> + pthread_barrier_destroy(¶ms->configured);
> + free(params);
> +
> return -ret;
> }
>
> --
> 2.29.2
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