Re: [PATCH v4 1/4] remoteproc: Traverse rproc_list under RCU read lock

Mathieu Poirier
2020-03-23T21:52:10Z

On Mon, Mar 09, 2020 at 11:38:14PM -0700, Bjorn Andersson wrote:
> In order to be able to traverse the mostly read-only rproc_list without
> locking during panic migrate traversal to be done under rcu_read_lock().
>
> Mutual exclusion for modifications of the list continues to be handled
> by the rproc_list_mutex and a synchronization point is added before
> releasing objects that are popped from the list.
>
> Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> ---
>
> Change v3:
> - New patch
>
> drivers/remoteproc/remoteproc_core.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> index 097f33e4f1f3..f0a77c30c6b1 100644
> --- a/drivers/remoteproc/remoteproc_core.c
> +++ b/drivers/remoteproc/remoteproc_core.c
> @@ -1854,8 +1854,8 @@ struct rproc *rproc_get_by_phandle(phandle phandle)
> if (!np)
> return NULL;
>
> - mutex_lock(&rproc_list_mutex);
> - list_for_each_entry(r, &rproc_list, node) {
> + rcu_read_lock();
> + list_for_each_entry_rcu(r, &rproc_list, node) {
> if (r->dev.parent && r->dev.parent->of_node == np) {
> /* prevent underlying implementation from being removed */
> if (!try_module_get(r->dev.parent->driver->owner)) {
> @@ -1868,7 +1868,7 @@ struct rproc *rproc_get_by_phandle(phandle phandle)
> break;
> }
> }
> - mutex_unlock(&rproc_list_mutex);
> + rcu_read_unlock();
>
> of_node_put(np);
>
> @@ -1925,7 +1925,7 @@ int rproc_add(struct rproc *rproc)
>
> /* expose to rproc_get_by_phandle users */
> mutex_lock(&rproc_list_mutex);
> - list_add(&rproc->node, &rproc_list);
> + list_add_rcu(&rproc->node, &rproc_list);
> mutex_unlock(&rproc_list_mutex);
>
> return 0;
> @@ -2140,9 +2140,12 @@ int rproc_del(struct rproc *rproc)
>
> /* the rproc is downref'ed as soon as it's removed from the klist */
> mutex_lock(&rproc_list_mutex);
> - list_del(&rproc->node);
> + list_del_rcu(&rproc->node);
> mutex_unlock(&rproc_list_mutex);
>
> + /* Ensure that no readers of rproc_list are still active */
> + synchronize_rcu();
> +

Please add linuc/rculist.h to include the RCU API. With that:

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>

> device_del(&rproc->dev);
>
> return 0;
> --
> 2.24.0
>