linux-kernel - RE: [RFC][PATCH v4 -next 1/4] Move kmsg_dump(KMSG_DUMP_PANIC) below smp_send

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Message-ID: <5C4C569E8A4B9B42A84A977CF070A35B2C5827B01D@USINDEVS01.corp.hds.com>
Date:	Thu, 5 Jan 2012 15:10:25 -0500
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	"Luck, Tony" <tony.luck@...el.com>, Don Zickus <dzickus@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Chen, Gong" <gong.chen@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Brown, Len" <len.brown@...el.com>,
	"'ying.huang@...el.com'" <'ying.huang@...el.com'>,
	"'ak@...ux.intel.com'" <'ak@...ux.intel.com'>,
	"'hughd@...omium.org'" <'hughd@...omium.org'>,
	"'mingo@...e.hu'" <'mingo@...e.hu'>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"namhyung@...il.com" <namhyung@...il.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: [RFC][PATCH v4 -next 1/4] Move kmsg_dump(KMSG_DUMP_PANIC) below
 smp_send_stop()


>Aren't you worried about the comment about smp_send_stop() not
>being hardened to work in a panic situation?
> 	/*
> 	 * Note smp_send_stop is the usual smp shutdown function, which
> 	 * unfortunately means it may not be hardened to work in a panic

This comment is wrong because Don improved smp_send_stop() by switching REBOOT_VECTOR to NMI.
And his patch has already merged to linux-next tree.

http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commitdiff;h=3603a2512f9e69dc87914ba922eb4a0812b21cd6

So, current smp_send_stop() is hardened to work in a panic situation.

I will remove this wrong comment.

Seiji

>-----Original Message-----
>From: Luck, Tony [mailto:tony.luck@...el.com]
>Sent: Thursday, January 05, 2012 2:07 PM
>To: Seiji Aguchi; Don Zickus
>Cc: linux-kernel@...r.kernel.org; Matthew Garrett; Vivek Goyal; Chen, Gong; akpm@...ux-foundation.org; Brown, Len;
>'ying.huang@...el.com'; 'ak@...ux.intel.com'; 'hughd@...omium.org'; 'mingo@...e.hu'; jmorris@...ei.org;
>a.p.zijlstra@...llo.nl; namhyung@...il.com; dle-develop@...ts.sourceforge.net; Satoru Moriya
>Subject: RE: [RFC][PATCH v4 -next 1/4] Move kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop()
>
>-	kmsg_dump(KMSG_DUMP_PANIC);
>-
> 	/*
> 	 * Note smp_send_stop is the usual smp shutdown function, which
> 	 * unfortunately means it may not be hardened to work in a panic
>@@ -117,6 +115,8 @@ void panic(const char *fmt, ...)
> 	 */
> 	smp_send_stop();
>
>+	kmsg_dump(KMSG_DUMP_PANIC);
>+
>
>Aren't you worried about the comment about smp_send_stop() not
>being hardened to work in a panic situation?
>
>If it does work - we are clearly much better off moving the
>kmsg_dump() call down like this. It makes life much simpler
>and cleaner to work with just one running cpu.
>
>But if something goes wrong - we might not see the dump at all!
>
>How do we compare these cases and decide that it is better to
>trust that smp_send_stop() will return?
>
>-Tony
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