netdev - Re: IPv4/IPv6 sysctl unregistration deadlock

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Date:	Thu, 26 Feb 2009 11:01:41 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Patrick McHardy <kaber@...sh.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: IPv4/IPv6 sysctl unregistration deadlock

Stephen Hemminger <shemminger@...tta.com> writes:

> What about something like this:
>
> Subject: [PATCH] Avoid race between network down and sysfs

As far as solutions go.  That looks like the easiest correct solution.
So.  
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Will -ERESTARTSYS trigger the in kernel restart logic in this case?

There are a lot more cases to cover, and I don't I like it long
term.  Spinning waiting for rtnl_lock feels wrong.  Plus it does
not help with discovering the problem in new sysfs, sysctl, or
proc files.

It has the major advantage that we can fix things now.

> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
>
> --- a/net/core/net-sysfs.c	2009-02-26 08:36:18.000000000 -0800
> +++ b/net/core/net-sysfs.c	2009-02-26 08:37:51.000000000 -0800
> @@ -77,7 +77,9 @@ static ssize_t netdev_store(struct devic
>  	if (endp == buf)
>  		goto err;
>  
> -	rtnl_lock();
> +	if (!rtnl_trylock())
> +		return -ERESTARTSYS;
> +
>  	if (dev_isalive(net)) {
>  		if ((ret = (*set)(net, new)) == 0)
>  			ret = len;
--
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