netdev - Re: [PATCH net-next] cxgb4: append firmware dump to vmcore in kernel panic

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Date:   Tue, 20 Feb 2018 16:51:03 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jakub Kicinski <kubakici@...pl>,
        Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>
Cc:     David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Ganesh GR <ganeshgr@...lsio.com>,
        Nirranjan Kirubaharan <nirranjan@...lsio.com>,
        Indranil Choudhury <indranil@...lsio.com>
Subject: Re: [PATCH net-next] cxgb4: append firmware dump to vmcore in kernel
 panic

On 02/20/2018 04:43 PM, Jakub Kicinski wrote:
> On Mon, 19 Feb 2018 18:04:17 +0530, Rahul Lakkireddy wrote:
>> Our requirement is to analyze the state of firmware/hardware at the
>> time of kernel panic. 
> 
> I was wondering about this since you posted the patch and I can't come
> up with any specific scenario where kernel crash would correlate
> clearly with device state in non-trivial way.
> 
> Perhaps there is something about cxgb4 HW/FW that makes this useful.
> Could you explain?  Could you give a real life example of a bug?  
> Is it related to the TOE-looking TLS offload Atul is posting?
> 
> Is the panic you're targeting here real or manually triggered from user
> space to get a full dump of kernel and FW?
> 
> That's me trying to guess what you're doing.. :)
> 

One case where this might be helpful is if you are chasing down DMA
corruption and you would like to get a nearly instant capture of both
the kernel's memory and the adapter which may be responsible for that.
This is not probably 100% proof because there is a timing window during
which the dumps of both contexts are going to happen, and that alone
might be influencing the captured memory view. Just guessing of course.
-- 
Florian