netdev - Re: [PATCH net] sfc: fix calling of free

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Message-ID: <536A8D6F.9090108@redhat.com>
Date:	Wed, 07 May 2014 21:45:51 +0200
From:	Nikolay Aleksandrov <nikolay@...hat.com>
To:	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org, linux-net-drivers@...arflare.com,
	sshah@...arflare.com
Subject: Re: [PATCH net] sfc: fix calling of free_irq with 0 argument

On 05/07/2014 09:39 PM, David Miller wrote:
> From: Nikolay Aleksandrov <nikolay@...hat.com>
> Date: Tue,  6 May 2014 14:49:16 +0200
> 
>> If the sfc driver is in legacy interrupt mode (either explicitly by
>> using interrupt_mode module param or by falling back to it) it will
>> hit a warning at kernel/irq/manage.c because it will try to free irq 0
>> in efx_nic_fini_interrupt() since the MSI interrupts were freed always,
>> but in legacy irq mode they're == 0. So fix it by checking if we
>> actually have an interrupt allocated and only then free it.
>>
>> CC: <linux-net-drivers@...arflare.com>
>> CC: Shradha Shah <sshah@...arflare.com>
>> CC: David S. Miller <davem@...emloft.net>
>>
>> Reported-by: Zenghui Shi <zshi@...hat.com>
>> Signed-off-by: Nikolay Aleksandrov <nikolay@...hat.com>
>> ---
>> There're other ways to fix this as well, but I chose this one as it follows
>> the logic in the code. Also I saw it used in a few places to check if
>> there's an IRQ allocated for that channel.
> 
> Zero can be a valid interrupt on some systems.
> 
> This is a discussion that keeps popping up from time to time, and Linus
> usually gets upset when someone adds a "!irq" test somewhere.
> 
> Why not just guard the efx_for_each_channel() loop with a top-level
> test of whether we are using legacy interrupt mode?  That will avoid
> this issue entirely.
> 
Yeah, that was my other solution - looking at the mode the card's in.
I'm fine both ways, like I said earlier I did it this way to be consistent
with the style used (it's used like that in other places, too).
And then I found out it's been like that before the commit I mentioned.

If the Solarflare folks are okay with it I can re-write the function to be
based on the mode used instead of checking for zero irq. I'll post an
adjusted patch after I get a chance to test it.

Nik

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