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

From: Toshi Kani <toshi.kani@hp.com>
To: Hanjun Guo <guohanjun@huawei.com>
Cc: "Luck, Tony" <tony.luck@intel.com>,
	"Yu, Fenghua" <fenghua.yu@intel.com>,
	"linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Jiang Liu <jiang.liu@huawei.com>,
	Eric Biederman <ebiederm@xmission.com>,
	Vivek Goyal <vgoyal@redhat.com>, Haren Myneni <hbabu@us.ibm.com>,
	Yinghai Lu <yinghai@kernel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
	Taku Izumi <izumi.taku@jp.fujitsu.com>,
	Wen Congyang <wency@cn.fujitsu.com>,
	Tang Chen <tangchen@cn.fujitsu.com>,
	Jianguo Wu <wujianguo@huawei.com>
Subject: Re: [BUGFIX PATCH][RESEND] kexec & iosapic: kexec oops when iosapic was removed
Date: Thu, 16 Aug 2012 13:33:17 -0600	[thread overview]
Message-ID: <1345145597.4732.21.camel@misato.fc.hp.com> (raw)
In-Reply-To: <502CCB38.1030705@huawei.com>

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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