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SubjectRe: [PATCH net-next] devlink: Execute devlink health recover as a work
On Thu, 25 Apr 2019 13:57:03 +0300, Moshe Shemesh wrote:
> Different reporters have different rules in the driver and are being
> created/destroyed during different stages of driver load/unload/running.
> So during execution of a reporter recover the flow can go through
> another reporter's destroy and create. Such flow leads to deadlock
> trying to lock a mutex already held if the flow was triggered by devlink
> recover command.
> To avoid such deadlock, we execute the recover flow from a workqueue.
> Once the recover work is done successfully the reporter health state and
> recover counter are being updated.

Naive question, why not just run the doit unlocked? Why the async?

> Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
> Signed-off-by: Jiri Pirko <jiri@mellanox.com>

One day we really gotta start documenting the context from which
things are called and locks called when ops are invoked.. :)

> diff --git a/net/core/devlink.c b/net/core/devlink.c
> index 7b91605..8ee380e 100644
> --- a/net/core/devlink.c
> +++ b/net/core/devlink.c
> @@ -4443,6 +4444,40 @@ struct devlink_health_reporter {
> return NULL;
> }
>
> +static int
> +devlink_health_reporter_recover(struct devlink_health_reporter *reporter,
> + void *priv_ctx)
> +{
> + int err;
> +
> + if (!reporter->ops->recover)
> + return -EOPNOTSUPP;
> +
> + err = reporter->ops->recover(reporter, priv_ctx);
> + if (err)
> + return err;
> +
> + reporter->recovery_count++;
> + reporter->health_state = DEVLINK_HEALTH_REPORTER_STATE_HEALTHY;
> + reporter->last_recovery_ts = jiffies;

Well, the dump looks at these without taking any locks..

> + trace_devlink_health_reporter_state_update(reporter->devlink,
> + reporter->ops->name,
> + reporter->health_state);
> + return 0;
> +}
> +
> +static void
> +devlink_health_reporter_recover_work(struct work_struct *work)
> +{
> + struct devlink_health_reporter *reporter;
> +
> + reporter = container_of(work, struct devlink_health_reporter,
> + recover_work);
> +
> + devlink_health_reporter_recover(reporter, NULL);
> +}
> +
> /**
> * devlink_health_reporter_create - create devlink health reporter
> *

> @@ -4483,6 +4518,8 @@ struct devlink_health_reporter *
> reporter->devlink = devlink;
> reporter->graceful_period = graceful_period;
> reporter->auto_recover = auto_recover;
> + INIT_WORK(&reporter->recover_work,
> + devlink_health_reporter_recover_work);
> mutex_init(&reporter->dump_lock);
> list_add_tail(&reporter->list, &devlink->reporter_list);
> unlock:
> @@ -4505,6 +4542,7 @@ struct devlink_health_reporter *
> mutex_unlock(&reporter->devlink->lock);
> if (reporter->dump_fmsg)
> devlink_fmsg_free(reporter->dump_fmsg);
> + cancel_work_sync(&reporter->recover_work);
> kfree(reporter);
> }
> EXPORT_SYMBOL_GPL(devlink_health_reporter_destroy);
> @@ -4526,26 +4564,6 @@ struct devlink_health_reporter *
> }
> EXPORT_SYMBOL_GPL(devlink_health_reporter_state_update);
>
> -static int
> -devlink_health_reporter_recover(struct devlink_health_reporter *reporter,
> - void *priv_ctx)
> -{
> - int err;
> -
> - if (!reporter->ops->recover)
> - return -EOPNOTSUPP;
> -
> - err = reporter->ops->recover(reporter, priv_ctx);
> - if (err)
> - return err;
> -
> - reporter->recovery_count++;
> - reporter->health_state = DEVLINK_HEALTH_REPORTER_STATE_HEALTHY;
> - reporter->last_recovery_ts = jiffies;
> -
> - return 0;
> -}
> -
> static void
> devlink_health_dump_clear(struct devlink_health_reporter *reporter)
> {
> @@ -4813,7 +4831,11 @@ static int devlink_nl_cmd_health_reporter_recover_doit(struct sk_buff *skb,
> if (!reporter)
> return -EINVAL;
>
> - return devlink_health_reporter_recover(reporter, NULL);
> + if (!reporter->ops->recover)
> + return -EOPNOTSUPP;
> +
> + queue_work(devlink->reporters_wq, &reporter->recover_work);
> + return 0;
> }

So the recover user space request will no longer return the status, and
it will not actually wait for the recover to happen. Leaving user
pondering - did the recover run and fail, or did it nor get run yet...

> static int devlink_nl_cmd_health_reporter_diagnose_doit(struct sk_buff *skb,
> @@ -5234,6 +5256,11 @@ struct devlink *devlink_alloc(const struct devlink_ops *ops, size_t priv_size)
> INIT_LIST_HEAD(&devlink->param_list);
> INIT_LIST_HEAD(&devlink->region_list);
> INIT_LIST_HEAD(&devlink->reporter_list);
> + devlink->reporters_wq = create_singlethread_workqueue("devlink_reporters");

Why is it single threaded?

> + if (!devlink->reporters_wq) {
> + kfree(devlink);
> + return NULL;
> + }
> mutex_init(&devlink->lock);
> return devlink;
> }
> @@ -5278,6 +5305,7 @@ void devlink_unregister(struct devlink *devlink)
> void devlink_free(struct devlink *devlink)
> {
> mutex_destroy(&devlink->lock);
> + destroy_workqueue(devlink->reporters_wq);
> WARN_ON(!list_empty(&devlink->reporter_list));
> WARN_ON(!list_empty(&devlink->region_list));
> WARN_ON(!list_empty(&devlink->param_list));

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