netdev - Re: [PATCH] rtnl: Simplify ASSERT

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Date:	Tue, 2 Oct 2007 17:29:11 +0200 (CEST)
From:	Patrick McHardy <kaber@...sh.net>
To:	Herbert Xu <herbert@...dor.apana.org.au>
cc:	"Eric W. Biederman" <ebiederm@...ssion.com>, davem@...emloft.net,
	netdev@...r.kernel.org, oliver@...kum.name,
	linux-usb-devel@...ts.sourceforge.net
Subject: Re: [PATCH] rtnl: Simplify ASSERT_RTNL

On Tue, 2 Oct 2007, Herbert Xu wrote:

> On Sun, Sep 30, 2007 at 05:47:30PM +0200, Patrick McHardy wrote:
>>
> I'm a bit uncomfortable with having a function (change_flags)
> that's sometimes in a sleepable context and sometimes running
> with BH disabled.
>
> So how about splitting up the unicast/multicast entry points
> as follows?

>
> [NET]: Restore multicast-only __dev_mc_upload
>
> As it is dev_set_rx_mode needs to cope with being called with
> or without the RTNL.  This is rather confusing when it comes
> to understanding what locks are being held at a particular
> point.
>
> Since the only path that calls it without the RTNL is in the
> multicast code, we could avoid the confusion by splitting that
> out.
>
> This patch restores the old __dev_mc_upload as a multicast-only
> variant of dev_set_rx_mode.  It also gets rid of the now-unused
> __dev_set_rx_mod and makes dev_set_rx_mode static since it's
> only used in net/core/dev.c.
>
> As a side-effect this fixes the warning triggered by the
> RTNL_ASSERT in __dev_set_promiscuity.

I think this doesn't completely fix it, when dev_unicast_add is
interrupted by dev_mc_add before the unicast changes are performed,
they will get committed in the dev_mc_add context, so we might still
call change_flags with BH disabled. Taking the TX lock around the
dev->uc_count and dev->uc_promisc checks and changes in __dev_set_rx_mode
should fix this.
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