Re: [PATCH net-next v1] netdevsim: Forbid devlink reload when adding or deleting ports

Leon Romanovsky
2021-08-05T13:51:39Z

On Thu, Aug 05, 2021 at 06:15:47AM -0700, Jakub Kicinski wrote:
> On Thu, 5 Aug 2021 14:05:41 +0300 Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@nvidia.com>
> >
> > In order to remove complexity in devlink core related to
> > devlink_reload_enable/disable, let's rewrite new_port/del_port
> > logic to rely on internal to netdevsim lock.
> >
> > We should protect only reload_down flow because it destroys nsim_dev,
> > which is needed for nsim_dev_port_add/nsim_dev_port_del to hold
> > port_list_lock.
>
> I don't understand why we only have to protect reload_down.

I assumed that if we succeeded to pass reload_down and we are in
reload_up stage, everything was already bailed out.

>
> What protects us from adding a port right after down? That'd hit a
> destroyed mutex, up wipes the port list etc...

You will have very similar crash to already existing one:
* parallel call to del_device and add_port will hit same issue.

The idea is not make netdevsim universally correct, but to ensure that
it doesn't crash immediately.

>
> > + nsim_bus_dev = nsim_dev->nsim_bus_dev;
> > + if (!mutex_trylock(&nsim_bus_dev->nsim_bus_reload_lock))
> > + return -EOPNOTSUPP;
>
> Why not -EBUSY?

This is what devlink_reload_disable() returns, so I kept same error.
It is not important at all.

What about the following change on top of this patch?

diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c
index a29ec264119d..62d033a1a557 100644
--- a/drivers/net/netdevsim/bus.c
+++ b/drivers/net/netdevsim/bus.c
@@ -196,6 +196,11 @@ new_port_store(struct device *dev, struct device_attribute *attr,
if (!mutex_trylock(&nsim_bus_dev->nsim_bus_reload_lock))
return -EBUSY;

+ if (nsim_bus_dev->in_reload) {
+ mutex_unlock(&nsim_bus_dev->nsim_bus_reload_lock);
+ return -EBUSY;
+ }
+
ret = nsim_dev_port_add(nsim_bus_dev, NSIM_DEV_PORT_TYPE_PF, port_index);
mutex_unlock(&nsim_bus_dev->nsim_bus_reload_lock);
return ret ? ret : count;
@@ -221,6 +226,11 @@ del_port_store(struct device *dev, struct device_attribute *attr,
if (!mutex_trylock(&nsim_bus_dev->nsim_bus_reload_lock))
return -EBUSY;

+ if (nsim_bus_dev->in_reload) {
+ mutex_unlock(&nsim_bus_dev->nsim_bus_reload_lock);
+ return -EBUSY;
+ }
+
ret = nsim_dev_port_del(nsim_bus_dev, NSIM_DEV_PORT_TYPE_PF, port_index);
mutex_unlock(&nsim_bus_dev->nsim_bus_reload_lock);
return ret ? ret : count;
diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
index ff5714209b86..53068e184c90 100644
--- a/drivers/net/netdevsim/dev.c
+++ b/drivers/net/netdevsim/dev.c
@@ -878,6 +878,7 @@ static int nsim_dev_reload_down(struct devlink *devlink, bool netns_change,
mutex_unlock(&nsim_bus_dev->nsim_bus_reload_lock);
return -EOPNOTSUPP;
}
+ nsim_bus_dev->in_reload = true;

nsim_dev_reload_destroy(nsim_dev);
mutex_unlock(&nsim_bus_dev->nsim_bus_reload_lock);
@@ -889,17 +890,26 @@ static int nsim_dev_reload_up(struct devlink *devlink, enum devlink_reload_actio
struct netlink_ext_ack *extack)
{
struct nsim_dev *nsim_dev = devlink_priv(devlink);
+ struct nsim_bus_dev *nsim_bus_dev;
+ int ret;
+
+ nsim_bus_dev = nsim_dev->nsim_bus_dev;
+ mutex_lock(&nsim_bus_dev->nsim_bus_reload_lock);
+ nsim_bus_dev->in_reload = false;

if (nsim_dev->fail_reload) {
/* For testing purposes, user set debugfs fail_reload
* value to true. Fail right away.
*/
NL_SET_ERR_MSG_MOD(extack, "User setup the reload to fail for testing purposes");
+ mutex_unlock(&nsim_bus_dev->nsim_bus_reload_lock);
return -EINVAL;
}

*actions_performed = BIT(DEVLINK_RELOAD_ACTION_DRIVER_REINIT);
- return nsim_dev_reload_create(nsim_dev, extack);
+ ret = nsim_dev_reload_create(nsim_dev, extack);
+ mutex_unlock(&nsim_bus_dev->nsim_bus_reload_lock);
+ return ret;
}

static int nsim_dev_info_get(struct devlink *devlink,
diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
index 1c20bcbd9d91..793c86dc5a9c 100644
--- a/drivers/net/netdevsim/netdevsim.h
+++ b/drivers/net/netdevsim/netdevsim.h
@@ -362,6 +362,7 @@ struct nsim_bus_dev {
struct nsim_vf_config *vfconfigs;
/* Lock for devlink->reload_enabled in netdevsim module */
struct mutex nsim_bus_reload_lock;
+ bool in_reload;
bool init;
};

Thanks