linux-kernel - Re: [EDT][PATCH 1/1] hw_breakpoint.c :cpu hotplug handling

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Message-id: <1973496787.315501431924391025.JavaMail.weblogic@ep2mlwas08c>
Date:	Mon, 18 May 2015 04:46:32 +0000 (GMT)
From:	Vaneet Narang <v.narang@...sung.com>
To:	Will Deacon <will.deacon@....com>,
	Maninder Singh <maninder1.s@...sung.com>
Cc:	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Amit Arora <amit.arora@...sung.com>,
	AJEET YADAV <ajeet.y@...sung.com>,
	AKHILESH KUMAR <akhilesh.k@...sung.com>
Subject: Re: [EDT][PATCH 1/1] hw_breakpoint.c :cpu hotplug handling

EP-2DAD0AFA905A4ACB804C4F82A001242F

On Wed, May 13, 2015 at 06:24:06AM +0100, Maninder Singh wrote:
>> EP-2DAD0AFA905A4ACB804C4F82A001242F
>> 
>> Subject: [PATCH 1/1] hw_breakpoint.c :cpu hotplug handling
>> 
>> This patch adds support for CPU hotplug, It re-installl all installed watchpoints and breakpoints
>> back on H/W in case of cpu-hot plug.

>Not sure why this is needed -- the scheduler should reinstall the
>breakpoints when the debugged task gets scheduled in via
>arch_install_hw_breakpoint.
>
>Will

I agree with you this reinstalling has to be either take care by scheduler or Debug tool. 
In current implementation we clear H/W registers but we don't clear slots (wp_on_reg / bp_on_reg) for both watchpoint or breakpoint.
So it makes mandatory for debug tool to uninstall breakpoints when CPU goes offline, because if we don't 
uninstall which I think is not required and when CPU comes online, we will not be able to reinstall them back because there will be no free slots.
Despite of the fact that H/W registers are free but still we wouldn't be able to install breakpoints.
Logically we should clear these slots or we should reinstall but if you think reinstall has to be taken care by scheduler or debugger
then at least we should clear these slots.

Regards,
Vaneet Narang