linux-kernel - Re: [PATCH net-next v2 0/2] kernel: add support to collect hardware logs in crash recovery kernel

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Date:   Mon, 26 Mar 2018 19:15:40 +0530
From:   Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        Ganesh GR <ganeshgr@...lsio.com>,
        Nirranjan Kirubaharan <nirranjan@...lsio.com>,
        Indranil Choudhury <indranil@...lsio.com>
Subject: Re: [PATCH net-next v2 0/2] kernel: add support to collect hardware
 logs in crash recovery kernel

On Saturday, March 03/24/18, 2018 at 20:50:52 +0530, Eric W. Biederman wrote:
> 
> Rahul Lakkireddy <rahul.lakkireddy@...lsio.com> writes:
> 
> > On production servers running variety of workloads over time, kernel
> > panic can happen sporadically after days or even months. It is
> > important to collect as much debug logs as possible to root cause
> > and fix the problem, that may not be easy to reproduce. Snapshot of
> > underlying hardware/firmware state (like register dump, firmware
> > logs, adapter memory, etc.), at the time of kernel panic will be very
> > helpful while debugging the culprit device driver.
> >
> > This series of patches add new generic framework that enable device
> > drivers to collect device specific snapshot of the hardware/firmware
> > state of the underlying device in the crash recovery kernel. In crash
> > recovery kernel, the collected logs are exposed via /sys/kernel/crashdd/
> > directory, which is copied by user space scripts for post-analysis.
> >
> > A kernel module crashdd is newly added. In crash recovery kernel,
> > crashdd exposes /sys/kernel/crashdd/ directory containing device
> > specific hardware/firmware logs.
> 
> Have you looked at instead of adding a sysfs file adding the dumps
> as additional elf notes in /proc/vmcore?
> 

I see the crash recovery kernel's memory is not present in any of the
the PT_LOAD headers.  So, makedumpfile is not collecting the dumps
that are in crash recovery kernel's memory.

Also, are you suggesting exporting the dumps themselves as PT_NOTE
instead?  I'll look into doing it this way.

> That should allow existing tools to capture your extended dump
> information with no code changes, and it will allow having a single file
> core dump for storing the information.
> 
> Both of which should mean something that will integrate better into
> existing flows.
> 
> The interface logic of the driver should be essentially the same.
> 
> 
> Also have you tested this and seen how well your current logic captures
> the device information?
> 

Yes, the hardware snapshot is pretty close to the state during kernel
panic.  It is better than risking not being able to collect anything
at all during kernel panic.

Thanks,
Rahul