Re: [PATCH] makedumpfile: cope with not-present mem section

From: piliu <piliu@redhat.com>
To: "Thadeu Lima de Souza Cascardo" <cascardo@canonical.com>,
	"HAGIO KAZUHITO(萩尾　一仁)" <k-hagio-ab@nec.com>
Cc: "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	Michal Hocko <mhocko@kernel.org>, Qian Cai <cai@lca.pw>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Oscar Salvador <osalvador@suse.de>
Subject: Re: [PATCH] makedumpfile: cope with not-present mem section
Date: Wed, 29 Apr 2020 17:32:11 +0800	[thread overview]
Message-ID: <769ddb8a-c845-04a6-0064-d674bbd04ae3@redhat.com> (raw)
In-Reply-To: <20200128193302.GC4080@calabresa>

Hi Kazu and Cascardo,

I encounter a weird problem when running makedumpfile on a s390 machine.

Our production kernel uses extreme sparse memory model, and has the
following:

in mm/sparse.c

#ifdef CONFIG_SPARSEMEM_EXTREME
struct mem_section **mem_section;
#else
struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
        ____cacheline_internodealigned_in_smp;
#endif

So in makedumpfile.c, get_mem_section(), it got a failed result when the
first call site to validate_mem_section(), then it should success at the
second call site to validate_mem_section(), which is inside if
(is_sparsemem_extreme()) condition.

But the actual result is not like expected.

After introducing
commit e113f1c974c820f9633dc0073eda525d7575f365    [PATCH] cope with
not-present mem section

I got two successful calls to validate_mem_section(), and finally failed
at the condition
		ret = symbol_valid ^ pointer_valid;
		if (!ret) {
			ERRMSG("Could not validate mem_section.\n");
		}

Do you have any idea?

Thanks,
Pingfan

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