netdev - Re: [PATCH rdma-next v2 13/17] RDMA/core: Get sum value of all counters when perform a sysfs stat read

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Date:   Wed, 22 May 2019 14:10:42 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Doug Ledford <dledford@...hat.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        Majd Dibbiny <majd@...lanox.com>,
        Mark Zhang <markz@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH rdma-next v2 13/17] RDMA/core: Get sum value of all
 counters when perform a sysfs stat read

On Mon, Apr 29, 2019 at 11:34:49AM +0300, Leon Romanovsky wrote:
> From: Mark Zhang <markz@...lanox.com>
> 
> Since a QP can only be bound to one counter, then if it is bound to a
> separate counter, for backward compatibility purpose, the statistic
> value must be:
> * stat of default counter
> + stat of all running allocated counters
> + stat of all deallocated counters (history stats)
> 
> Signed-off-by: Mark Zhang <markz@...lanox.com>
> Reviewed-by: Majd Dibbiny <majd@...lanox.com>
> Signed-off-by: Leon Romanovsky <leonro@...lanox.com>
>  drivers/infiniband/core/counters.c | 99 +++++++++++++++++++++++++++++-
>  drivers/infiniband/core/device.c   |  8 ++-
>  drivers/infiniband/core/sysfs.c    | 10 ++-
>  include/rdma/rdma_counter.h        |  5 +-
>  4 files changed, 113 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/infiniband/core/counters.c b/drivers/infiniband/core/counters.c
> index 36cd9eca1e46..f598b1cdb241 100644
> +++ b/drivers/infiniband/core/counters.c
> @@ -146,6 +146,20 @@ static int __rdma_counter_bind_qp(struct rdma_counter *counter,
>  	return ret;
>  }
>  
> +static void counter_history_stat_update(const struct rdma_counter *counter)
> +{
> +	struct ib_device *dev = counter->device;
> +	struct rdma_port_counter *port_counter;
> +	int i;
> +
> +	port_counter = &dev->port_data[counter->port].port_counter;
> +	if (!port_counter->hstats)
> +		return;
> +
> +	for (i = 0; i < counter->stats->num_counters; i++)
> +		port_counter->hstats->value[i] += counter->stats->value[i];
> +}
> +
>  static int __rdma_counter_unbind_qp(struct ib_qp *qp, bool force)
>  {
>  	struct rdma_counter *counter = qp->counter;
> @@ -285,8 +299,10 @@ int rdma_counter_unbind_qp(struct ib_qp *qp, bool force)
>  		return ret;
>  
>  	rdma_restrack_put(&counter->res);
> -	if (atomic_dec_and_test(&counter->usecnt))
> +	if (atomic_dec_and_test(&counter->usecnt)) {
> +		counter_history_stat_update(counter);
>  		rdma_counter_dealloc(counter);
> +	}
>  
>  	return 0;
>  }
> @@ -307,21 +323,98 @@ int rdma_counter_query_stats(struct rdma_counter *counter)
>  	return ret;
>  }
>  
> -void rdma_counter_init(struct ib_device *dev)
> +static u64 get_running_counters_hwstat_sum(struct ib_device *dev,
> +					   u8 port, u32 index)
> +{
> +	struct rdma_restrack_entry *res;
> +	struct rdma_restrack_root *rt;
> +	struct rdma_counter *counter;
> +	unsigned long id = 0;
> +	u64 sum = 0;
> +
> +	rt = &dev->res[RDMA_RESTRACK_COUNTER];
> +	xa_lock(&rt->xa);
> +	xa_for_each(&rt->xa, id, res) {
> +		if (!rdma_restrack_get(res))
> +			continue;

Why do we need to get refcounts if we are holding the xa_lock?

> +
> +		counter = container_of(res, struct rdma_counter, res);
> +		if ((counter->device != dev) || (counter->port != port))
> +			goto next;
> +
> +		if (rdma_counter_query_stats(counter))
> +			goto next;

And rdma_counter_query_stats does

+	mutex_lock(&counter->lock);

So this was never tested as it will insta-crash with lockdep.

Presumably this is why it is using xa_for_each and restrack_get - but
it needs to drop the lock after successful get.

This sort of comment applies to nearly evey place in this series that
uses xa_for_each. 

This needs to be tested with lockdep.

Jason