linux-kernel - Re: [BUGFIX PATCH][RESEND] kexec & iosapic: kexec oops when iosapic was removed

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Date:	Thu, 16 Aug 2012 13:33:17 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Hanjun Guo <guohanjun@...wei.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Haren Myneni <hbabu@...ibm.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Jianguo Wu <wujianguo@...wei.com>
Subject: Re: [BUGFIX PATCH][RESEND] kexec & iosapic: kexec oops when iosapic
 was removed

On Thu, 2012-08-16 at 18:28 +0800, Hanjun Guo wrote:
> On 2012/8/13 10:54, Luck, Tony wrote:
> >> 		vec = irq_to_vector(irq);
> >> 		list_for_each_entry(rte, &info->rtes,
> >> 				rte_list) {
> >> +			if (rte->refcnt == NO_REF_RTE)
> >> +				continue;
> >> +
> >> 			iosapic_write(rte->iosapic,
> >> 					IOSAPIC_RTE_LOW(rte->rte_index),
> >> 					IOSAPIC_MASK|vec);
> > 
> > This will work - but is it papering over a problem when you removed the
> > iosapic? Should we really have removed this "rte" from rte_list when the
> > iosapic was removed?
> > 
> > -Tony
> > 
> 
> Hi Tony,
>     Thanks for your comments, and sorry for the late reply.
> 
> We only set rte->refcnt to NO_REF_RTE if no device attach to this RTE when
> unregister a GSI, and increase the rte->refcnt if the RTE is already existing
> when register a GSI, so "rte" will not removed from rte_list when the
> iosapic is removed.

Hi Hanjun,

I think updating rte->refcnt makes sense as long as rte->iosapic points
to a valid iosapic entry.  It looks odd to me that rte->iosapic is left
pointing an invalid iosapic entry after this iosapic is removed.  So, I
agree with Tony's concern.

Thanks,
-Toshi


> Actually, the rte_list will keep static when remove/add a existing iosapic
> after boot up.
> 
> Should we remove the RTE from the rte_list? if yes, we will have more
> to do than this patch.
> 
> Thanks
> Hanjun Guo
> 
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