linux-kernel - Re: [PATCH] net/mlx5e: fix high stack usage

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Date:   Fri, 2 Nov 2018 22:07:02 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "eric.dumazet@...il.com" <eric.dumazet@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "arnd@...db.de" <arnd@...db.de>,
        "leon@...nel.org" <leon@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Moshe Shemesh <moshe@...lanox.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Boris Pismenny <borisp@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Ilya Lesokhin <ilyal@...lanox.com>,
        Kamal Heib <kamalh@...lanox.com>
Subject: Re: [PATCH] net/mlx5e: fix high stack usage

On Fri, 2018-11-02 at 14:39 -0700, Eric Dumazet wrote:
> 
> On 11/02/2018 02:05 PM, Saeed Mahameed wrote:
>  
> > temp will be mem copied to priv->stats.sw at the end,
> > memcpy(&priv->stats.sw, &s, sizeof(s)); 
> > 
> > one other way to solve this as suggested by Andrew, is to get rid
> > of
> > the temp var and make it point directly to priv->stats.sw 
> > 
> 
> What about concurrency ?
> 
> This temp variable is there to make sure concurrent readers of stats
> might
> not see mangle data (because another 'reader' just did a memset() and
> is doing the folding)
> 
> 
> mlx5e_get_stats() can definitely be run at the same time by multiple
> threads.
> 

hmm, you are right, i was thinking that mlx5e_get_Stats will trigger a
work to update stats and grab the state_lock, but for sw stats this is
not the case it is done in place.

BTW memcpy itself is not thread safe.