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Sun, 9 Feb 2020 13:50:21 +0000 (UTC) Received: from localhost (ovpn-12-31.pek2.redhat.com [10.72.12.31]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9444187B0A; Sun, 9 Feb 2020 13:50:18 +0000 (UTC) Date: Sun, 9 Feb 2020 21:50:15 +0800 From: Baoquan He To: Wei Yang Cc: Dan Williams , Wei Yang , Andrew Morton , Oscar Salvador , Linux MM , Linux Kernel Mailing List , David Hildenbrand Subject: Re: [PATCH 2/3] mm/sparsemem: get physical address to page struct instead of virtual address to pfn Message-ID: <20200209135015.GX8965@MiWiFi-R3L-srv> References: <20200206231629.14151-1-richardw.yang@linux.intel.com> <20200206231629.14151-3-richardw.yang@linux.intel.com> <20200207112632.5inklkwyiewhrd75@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200207112632.5inklkwyiewhrd75@master> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 02/07/20 at 11:26am, Wei Yang wrote: > On Thu, Feb 06, 2020 at 06:19:46PM -0800, Dan Williams wrote: > >On Thu, Feb 6, 2020 at 3:17 PM Wei Yang wrote: > >> > >> memmap should be the physical address to page struct instead of virtual > >> address to pfn. > >> > >> Since we call this only for SPARSEMEM_VMEMMAP, pfn_to_page() is valid at > >> this point. > >> > >> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > >> Signed-off-by: Wei Yang > >> CC: Dan Williams > >> --- > >> mm/sparse.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/mm/sparse.c b/mm/sparse.c > >> index b5da121bdd6e..56816f653588 100644 > >> --- a/mm/sparse.c > >> +++ b/mm/sparse.c > >> @@ -888,7 +888,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn, > >> /* Align memmap to section boundary in the subsection case */ > >> if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) && > >> section_nr_to_pfn(section_nr) != start_pfn) > >> - memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr)); > >> + memmap = pfn_to_page(section_nr_to_pfn(section_nr)); > > > >Yes, this looks obviously correct. This might be tripping up > >makedumpfile. Do you see any practical effects of this bug? The kernel > >mostly avoids ->section_mem_map in the vmemmap case and in the > >!vmemmap case section_nr_to_pfn(section_nr) should always equal > >start_pfn. > > I took another look into the code. Looks there is no practical effect after > this. Because in the vmemmap case, we don't need ->section_mem_map to retrieve > the real memmap. > > But leave a inconsistent data in section_mem_map is not a good practice. Yeah, it does has no pratical effect. I tried to create sub-section alighed namespace, then trigger crash, makedumpfile isn't impacted. Because pmem memory is only added, but not onlined. We don't report it to kdump, makedumpfile will ignore it. I think it's worth fixing it to encode a correct memmap address. We don't know if in the future this will break anything. Thanks Baoquan