netdev - Re: [PATCH 2.6.20-rc3]: 8139cp: Don't blindly enable interrupts

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Message-ID: <45AFC115.4090503@redhat.com>
Date:	Thu, 18 Jan 2007 13:48:53 -0500
From:	Chris Lalancette <clalance@...hat.com>
To:	Jeff Garzik <jgarzik@...ox.com>
CC:	Francois Romieu <romieu@...zoreil.com>, netdev@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.20-rc3]: 8139cp: Don't blindly enable interrupts

Jeff Garzik wrote:

> Chris Lalancette wrote:
>
>> Francois Romieu wrote:
>>
>>> Chris Lalancette <clalance@...hat.com> :
>>> [...]
>>>  
>>>
>>>>     Thanks for the comments.  While the patch you sent will help,
>>>> there are
>>>> still other places that will have problems.  For example, in
>>>> netpoll_send_skb,
>>>> we call local_irq_save(flags), then call dev->hard_start_xmit(),
>>>> and then call
>>>> local_irq_restore(flags).  This is a similar situation to what I
>>>> described
>>>> above; we will re-enable interrupts in cp_start_xmit(), when
>>>> netpoll_send_skb
>>>> doesn't expect that, and will probably run into issues.
>>>>     Is there a problem with changing cp_start_xmit to use the
>>>> spin_lock_irqsave(), besides the extra instructions it needs?
>>>>   
>>>
>>> No. Given the history of locking in netpoll and the content of
>>> Documentation/networking/netdevices.txt, asking Herbert which rule(s)
>>> the code is supposed to follow seemed safer to me.
>>>
>>> You can forget my patch.
>>>
>>> Please resend your patch inlined to Jeff as described in
>>> http://linux.yyz.us/patch-format.html.
>>>
>>>  
>>>
>> Francois,
>>      Great.  Resending mail, shortening subject to < 65 characters and
>> inlining the patch.
>>
>> Thanks,
>> Chris Lalancette
>>
>> Similar to this commit:
>>
>> http://kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=d15e9c4d9a75702b30e00cdf95c71c88e3f3f51e
>>
>>
>> It's not safe in cp_start_xmit to blindly call spin_lock_irq and then
>> spin_unlock_irq, since it may very well be the case that cp_start_xmit
>> was called with interrupts already disabled (I came across this bug in
>> the context of netdump in RedHat kernels, but the same issue holds, for
>> example, in netconsole). Therefore, replace all instances of
>> spin_lock_irq and spin_unlock_irq with spin_lock_irqsave and
>> spin_unlock_irqrestore, respectively, in cp_start_xmit(). I tested this
>> against a fully-virtualized Xen guest using netdump, which happens to
>> use the 8139cp driver to talk to the emulated hardware. I don't have a
>> real piece of 8139cp hardware to test on, so someone else will have to
>> do that.
>>
>> Signed-off-by: Chris Lalancette <clalance@...hat.com>
>
>
> applied.
>
> In the future, please remove the quoted emails stuff, and anything
> else that does not belong in the kernel changelog.  It must be
> hand-edited out, before using git-am to merge your patch into the
> kernel tree.
>
>     Jeff
>
>
>
Jeff,
     Ah, I see.  Noted.  Thanks.

Chris Lalancette
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