netdev - Re: [PATCH net] devlink: protect devlink dump by the instance lock

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Date:   Thu, 15 Dec 2022 20:44:47 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
        jacob.e.keller@...el.com, jiri@...dia.com, moshe@...lanox.com
Subject: Re: [PATCH net] devlink: protect devlink dump by the instance lock

On Thu, 15 Dec 2022 20:41:22 -0800 Jakub Kicinski wrote:
> Take the instance lock around devlink_nl_fill() when dumping,
> doit takes it already.
> 
> We are only dumping basic info so in the worst case we were risking
> data races around the reload statistics. Also note that the reloads
> themselves had not been under the instance lock until recently, so
> the selection of the Fixes tag is inherently questionable.
> 
> Fixes: a254c264267e ("devlink: Add reload stats")

On second thought, the drivers can't call reload, so until we got rid
of the big bad mutex there could have been no race. I'll swap the tag
for:

Fixes: d3efc2a6a6d8 ("net: devlink: remove devlink_mutex")

when/if applying.

> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> CC: jiri@...dia.com
> CC: moshe@...lanox.com
> ---
>  net/core/devlink.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/core/devlink.c b/net/core/devlink.c
> index d2df30829083..032d6d0a5ce6 100644
> --- a/net/core/devlink.c
> +++ b/net/core/devlink.c
> @@ -1648,10 +1648,13 @@ static int devlink_nl_cmd_get_dumpit(struct sk_buff *msg,
>  			continue;
>  		}
>  
> +		devl_lock(devlink);
>  		err = devlink_nl_fill(msg, devlink, DEVLINK_CMD_NEW,
>  				      NETLINK_CB(cb->skb).portid,
>  				      cb->nlh->nlmsg_seq, NLM_F_MULTI);
> +		devl_unlock(devlink);
>  		devlink_put(devlink);
> +
>  		if (err)
>  			goto out;
>  		idx++;