Re: [PATCH net-next 4/9] devlink: always check if the devlink instance is registered

[Jiri Pirko <jiri@resnulli.us>]

Fri, Jan 06, 2023 at 07:33:57AM 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.
>
>Signed-off-by: Jakub Kicinski <kuba@kernel.org>
>---
> net/devlink/core.c          | 19 +++++++++++++++----
> net/devlink/devl_internal.h |  8 ++++++++
> net/devlink/leftover.c      | 35 +++++++++++++++++++++++++++++------
> net/devlink/netlink.c       | 10 ++++++++--
> 4 files changed, 60 insertions(+), 12 deletions(-)
>
>diff --git a/net/devlink/core.c b/net/devlink/core.c
>index d3b8336946fd..c53c996edf1d 100644
>--- a/net/devlink/core.c
>+++ b/net/devlink/core.c
>@@ -67,6 +67,15 @@ void devl_unlock(struct devlink *devlink)
> }
> EXPORT_SYMBOL_GPL(devl_unlock);
> 
>+/**
>+ * 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_registered() after taking
>+ * the instance lock to check registration status.
>+ */
> struct devlink *__must_check devlink_try_get(struct devlink *devlink)
> {
> 	if (refcount_inc_not_zero(&devlink->refcount))
>@@ -300,10 +309,12 @@ 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_registered(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/devl_internal.h b/net/devlink/devl_internal.h
>index 6342552e5f99..01a00df81d0e 100644
>--- a/net/devlink/devl_internal.h
>+++ b/net/devlink/devl_internal.h
>@@ -86,6 +86,14 @@ extern struct genl_family devlink_nl_family;
> 
> struct devlink *devlinks_xa_find_get(struct net *net, unsigned long *indexp);
> 
>+static inline bool devl_is_registered(struct devlink *devlink)
>+{
>+	/* To prevent races the caller must hold the instance lock
>+	 * or another lock taken during unregistration.
>+	 */
>+	return xa_get_mark(&devlinks, devlink->index, DEVLINK_REGISTERED);
>+}
>+
> /* Netlink */
> #define DEVLINK_NL_FLAG_NEED_PORT		BIT(0)
> #define DEVLINK_NL_FLAG_NEED_DEVLINK_OR_PORT	BIT(1)
>diff --git a/net/devlink/leftover.c b/net/devlink/leftover.c
>index bec408da4dbe..491f821c8b77 100644
>--- a/net/devlink/leftover.c
>+++ b/net/devlink/leftover.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_registered(devlink))
>+			goto next_devlink;
>+
> 		list_for_each_entry(linecard, &devlink->linecard_list, list) {
> 			if (idx < state->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_registered(devlink)) {

Good. I have patchset to remove this and linecard lock prepared. That
makes things smoother.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>



>+			mutex_unlock(&devlink->reporters_lock);
>+			devlink_put(devlink);
>+			continue;
>+		}
>+
> 		list_for_each_entry(reporter, &devlink->reporter_list,
> 				    list) {
> 			if (idx < state->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_registered(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_registered(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_registered(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/netlink.c b/net/devlink/netlink.c
>index 69111746f5d9..b5b8ac6db2d1 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_registered(devlink) &&
>+		    strcmp(devlink->dev->bus->name, busname) == 0 &&
> 		    strcmp(dev_name(devlink->dev), devname) == 0)
> 			return devlink;
> 		devl_unlock(devlink);
>@@ -211,7 +212,12 @@ int devlink_nl_instance_iter_dump(struct sk_buff *msg,
> 
> 	devlink_dump_for_each_instance_get(msg, state, devlink) {
> 		devl_lock(devlink);
>-		err = cmd->dump_one(msg, devlink, cb);
>+
>+		if (devl_is_registered(devlink))
>+			err = cmd->dump_one(msg, devlink, cb);
>+		else
>+			err = 0;
>+
> 		devl_unlock(devlink);
> 		devlink_put(devlink);
> 
>-- 
>2.38.1
>