netdev - Re: Printing the driver name as part of the netdev watchdog message

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Date:	Mon, 07 Jul 2008 15:57:23 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	rdreier@...co.com
Cc:	shemminger@...tta.com, arjan@...radead.org, netdev@...r.kernel.org
Subject: Re: Printing the driver name as part of the netdev watchdog message

From: Roland Dreier <rdreier@...co.com>
Date: Mon, 07 Jul 2008 15:45:38 -0700

>  > > For consistency each call through ethtool_ops should
>  > > be holding rtnl mutex. And since dev_watchdog is a timer routine,
>  > > it is not safe to acquire a mutex there.
>  > 
>  > I think "get driver info", which does nothing but copy strings out of
>  > the driver software state, is a safe exception to these strict locking
>  > rules.
> 
> it seems that's not universally the case, eg get_drvinfo() in
> drivers/net/cxgb3/cxgb3_main.c does
> 
> 	t3_get_fw_version(adapter, &fw_vers);
> 	t3_get_tp_version(adapter, &tp_vers);
> 
> and from reading further in the code it's not obvious that this is safe
> to do without serialization (it calls into t3_read_flash(), which does a
> typical "write address reg, read data reg" sequence to access flash,
> without any locking).

I doubt it uses the RTNL semaphore elsewhere to protect
against this path, which is the only protection these
calls currently have.

Please don't bring up scarecrows, this looks like simply
a bug which already exists.
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