Re: [RFC net-next 04/10] devlink: always check if the devlink instance is registered

Jiri Pirko
2023-01-02T13:58:30Z

Sat, Dec 17, 2022 at 02:19:47AM CET, kuba@kernel.org wrote:
>Always check under the instance lock whether the devlink instance
>is still / already registered.
>
>This is a no-op for the most part, as the unregistration path currently
>waits for all references. On the init path, however, we may temporarily
>open up a race with netdev code, if netdevs are registered before the
>devlink instance. This is temporary, the next change fixes it, and this
>commit has been split out for the ease of review.
>
>Note that in case of iterating over sub-objects which have their
>own lock (regions and line cards) we assume an implicit dependency
>between those objects existing and devlink unregistration.

This would be probably very valuable to add as a comment inside the code
for the future reader mind sake.

>
>Signed-off-by: Jakub Kicinski <kuba@kernel.org>
>---
> include/net/devlink.h | 1 +
> net/devlink/basic.c | 35 +++++++++++++++++++++++++++++------
> net/devlink/core.c | 25 +++++++++++++++++++++----
> net/devlink/netlink.c | 10 ++++++++--
> 4 files changed, 59 insertions(+), 12 deletions(-)
>
>diff --git a/include/net/devlink.h b/include/net/devlink.h
>index 6a2e4f21779f..36e013d3aa52 100644
>--- a/include/net/devlink.h
>+++ b/include/net/devlink.h
>@@ -1626,6 +1626,7 @@ struct device *devlink_to_dev(const struct devlink *devlink);
> void devl_lock(struct devlink *devlink);
> int devl_trylock(struct devlink *devlink);
> void devl_unlock(struct devlink *devlink);
>+bool devl_is_alive(struct devlink *devlink);
> void devl_assert_locked(struct devlink *devlink);
> bool devl_lock_is_held(struct devlink *devlink);
>
>diff --git a/net/devlink/basic.c b/net/devlink/basic.c
>index 5f33d74eef83..6b18e70a39fd 100644
>--- a/net/devlink/basic.c
>+++ b/net/devlink/basic.c
>@@ -2130,6 +2130,9 @@ static int devlink_nl_cmd_linecard_get_dumpit(struct sk_buff *msg,
> int idx = 0;
>
> mutex_lock(&devlink->linecards_lock);
>+ if (!devl_is_alive(devlink))
>+ goto next_devlink;
>+
> list_for_each_entry(linecard, &devlink->linecard_list, list) {
> if (idx < dump->idx) {
> idx++;
>@@ -2151,6 +2154,7 @@ static int devlink_nl_cmd_linecard_get_dumpit(struct sk_buff *msg,
> }
> idx++;
> }
>+next_devlink:
> mutex_unlock(&devlink->linecards_lock);
> devlink_put(devlink);
> }
>@@ -7809,6 +7813,12 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
> int idx = 0;
>
> mutex_lock(&devlink->reporters_lock);
>+ if (!devl_is_alive(devlink)) {
>+ mutex_unlock(&devlink->reporters_lock);
>+ devlink_put(devlink);
>+ continue;
>+ }
>+
> list_for_each_entry(reporter, &devlink->reporter_list,
> list) {
> if (idx < dump->idx) {
>@@ -7830,6 +7840,9 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
> mutex_unlock(&devlink->reporters_lock);
>
> devl_lock(devlink);
>+ if (!devl_is_alive(devlink))
>+ goto next_devlink;
>+
> xa_for_each(&devlink->ports, port_index, port) {
> mutex_lock(&port->reporters_lock);
> list_for_each_entry(reporter, &port->reporter_list, list) {
>@@ -7853,6 +7866,7 @@ devlink_nl_cmd_health_reporter_get_dumpit(struct sk_buff *msg,
> }
> mutex_unlock(&port->reporters_lock);
> }
>+next_devlink:
> devl_unlock(devlink);
> devlink_put(devlink);
> }
>@@ -12218,7 +12232,8 @@ void devlink_compat_running_version(struct devlink *devlink,
> return;
>
> devl_lock(devlink);
>- __devlink_compat_running_version(devlink, buf, len);
>+ if (devl_is_alive(devlink))
>+ __devlink_compat_running_version(devlink, buf, len);
> devl_unlock(devlink);
> }
>
>@@ -12227,20 +12242,28 @@ int devlink_compat_flash_update(struct devlink *devlink, const char *file_name)
> struct devlink_flash_update_params params = {};
> int ret;
>
>- if (!devlink->ops->flash_update)
>- return -EOPNOTSUPP;
>+ devl_lock(devlink);
>+ if (!devl_is_alive(devlink)) {
>+ ret = -ENODEV;
>+ goto out_unlock;
>+ }
>+
>+ if (!devlink->ops->flash_update) {
>+ ret = -EOPNOTSUPP;
>+ goto out_unlock;
>+ }
>
> ret = request_firmware(&params.fw, file_name, devlink->dev);
> if (ret)
>- return ret;
>+ goto out_unlock;
>
>- devl_lock(devlink);
> devlink_flash_update_begin_notify(devlink);
> ret = devlink->ops->flash_update(devlink, &params, NULL);
> devlink_flash_update_end_notify(devlink);
>- devl_unlock(devlink);
>
> release_firmware(params.fw);
>+out_unlock:
>+ devl_unlock(devlink);
>
> return ret;
> }
>diff --git a/net/devlink/core.c b/net/devlink/core.c
>index d3b8336946fd..2abad8247597 100644
>--- a/net/devlink/core.c
>+++ b/net/devlink/core.c
>@@ -67,6 +67,21 @@ void devl_unlock(struct devlink *devlink)
> }
> EXPORT_SYMBOL_GPL(devl_unlock);
>
>+bool devl_is_alive(struct devlink *devlink)

Why "alive"? To be consistent with the existing terminology, how about
to name it devl_is_registered()?

Also, "devl_" implicates that it should be called with devlink instance
lock held, so probably devlink_is_registered() would be better.

>+{
>+ return xa_get_mark(&devlinks, devlink->index, DEVLINK_REGISTERED);
>+}
>+EXPORT_SYMBOL_GPL(devl_is_alive);
>+
>+/**
>+ * devlink_try_get() - try to obtain a reference on a devlink instance
>+ * @devlink: instance to reference
>+ *
>+ * Obtain a reference on a devlink instance. A reference on a devlink instance
>+ * only implies that it's safe to take the instance lock. It does not imply
>+ * that the instance is registered, use devl_is_alive() after taking
>+ * the instance lock to check registration status.
>+ */

This comment is not related to the patch, should be added in a separate
one.

> struct devlink *__must_check devlink_try_get(struct devlink *devlink)
> {
> if (refcount_inc_not_zero(&devlink->refcount))
>@@ -300,10 +315,12 @@ static void __net_exit devlink_pernet_pre_exit(struct net *net)
> devlinks_xa_for_each_registered_get(net, index, devlink) {
> WARN_ON(!(devlink->features & DEVLINK_F_RELOAD));
> devl_lock(devlink);
>- err = devlink_reload(devlink, &init_net,
>- DEVLINK_RELOAD_ACTION_DRIVER_REINIT,
>- DEVLINK_RELOAD_LIMIT_UNSPEC,
>- &actions_performed, NULL);
>+ err = 0;
>+ if (devl_is_alive(devlink))
>+ err = devlink_reload(devlink, &init_net,
>+ DEVLINK_RELOAD_ACTION_DRIVER_REINIT,
>+ DEVLINK_RELOAD_LIMIT_UNSPEC,
>+ &actions_performed, NULL);
> devl_unlock(devlink);
> devlink_put(devlink);
>
>diff --git a/net/devlink/netlink.c b/net/devlink/netlink.c
>index b38df704be1c..773efaabb6ad 100644
>--- a/net/devlink/netlink.c
>+++ b/net/devlink/netlink.c
>@@ -98,7 +98,8 @@ devlink_get_from_attrs_lock(struct net *net, struct nlattr **attrs)
>
> devlinks_xa_for_each_registered_get(net, index, devlink) {
> devl_lock(devlink);
>- if (strcmp(devlink->dev->bus->name, busname) == 0 &&
>+ if (devl_is_alive(devlink) &&
>+ strcmp(devlink->dev->bus->name, busname) == 0 &&
> strcmp(dev_name(devlink->dev), devname) == 0)
> return devlink;
> devl_unlock(devlink);
>@@ -210,7 +211,12 @@ int devlink_instance_iter_dump(struct sk_buff *msg, struct netlink_callback *cb)
>
> devlink_dump_for_each_instance_get(msg, dump, devlink) {
> devl_lock(devlink);
>- err = cmd->dump_one(msg, devlink, cb);
>+
>+ if (devl_is_alive(devlink))
>+ err = cmd->dump_one(msg, devlink, cb);
>+ else
>+ err = 0;
>+
> devl_unlock(devlink);
> devlink_put(devlink);
>
>--
>2.38.1
>