linux-kernel - Re: [PATCH v2] Add hard/soft lockup debugger entry points

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Message-ID: <56A7AB5B.2000000@ezchip.com>
Date:	Tue, 26 Jan 2016 12:22:35 -0500
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Jeff Merkey <linux.mdb@...il.com>, <linux-kernel@...r.kernel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Don Zickus <dzickus@...hat.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Aaron Tomlin <atomlin@...hat.com>,
	Michal Hocko <mhocko@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tejun Heo <tj@...nel.org>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
Subject: Re: [PATCH v2] Add hard/soft lockup debugger entry points

On 01/26/2016 12:04 PM, Jeff Merkey wrote:
> This patch adds an export which can be set by system debuggers to direct
> the hard lockup and soft lockup detector to trigger a breakpoint exception
> and enter a debugger if one is active.  It is assumed that if someone
> sets this variable, then an breakpoint handler of some sort will be actively
> loaded or registered via the notify die handler chain.
>
> This addition is extremely useful for debugging hard and soft lockups
> real time and quickly from a console debugger.
>
> Signed-off-by: Jeff Merkey<linux.mdb@...il.com>
> ---
>   kernel/watchdog.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)

You probably should reach out to someone who uses this stuff more
regularly - I actually wonder if the kgdb_breakpoint() API is the
right thing, though, not the internal arch_kgdb_breakpoint().

Of course any of these strategies also assume you are building
the kernel with CONFIG_KGDB set, and I'm pretty sure will cause
your build to fail if it isn't.  You likely need to guard this
stuff locally within watchdog.c for !CONFIG_KGDB.

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com