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

Bjorn Andersson
2020-03-10T06:39:56Z

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();
+
device_del(&rproc->dev);

return 0;
--
2.24.0