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Tue, 11 Dec 2018 14:24:16 -0800 (PST) Date: Tue, 11 Dec 2018 22:24:15 +0000 From: Wei Yang To: Zaslonko Mikhail Cc: Wei Yang , Michal Hocko , Mikhail Zaslonko , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Pavel.Tatashin@microsoft.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, gerald.schaefer@de.ibm.com Subject: Re: [PATCH 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section Message-ID: <20181211222415.yfco6l2dmywxgid7@master> Reply-To: Wei Yang References: <20181210130712.30148-1-zaslonko@linux.ibm.com> <20181210130712.30148-2-zaslonko@linux.ibm.com> <20181210132451.GO1286@dhcp22.suse.cz> <20181211094938.3mykr3n3tp6rfz4p@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 11, 2018 at 04:17:34PM +0100, Zaslonko Mikhail wrote: > > >On 11.12.2018 10:49, Wei Yang wrote: >> On Mon, Dec 10, 2018 at 02:24:51PM +0100, Michal Hocko wrote: >>> On Mon 10-12-18 14:07:12, Mikhail Zaslonko wrote: >>>> If memory end is not aligned with the sparse memory section boundary, the >>>> mapping of such a section is only partly initialized. >>> >>> It would be great to mention how you can end up in the situation like >>> this(a user provided memmap or a strange HW). >>> >>>> This may lead to >>>> VM_BUG_ON due to uninitialized struct page access from >>>> is_mem_section_removable() or test_pages_in_a_zone() function triggered by >>>> memory_hotplug sysfs handlers: >>>> >>>> page:000003d082008000 is uninitialized and poisoned >>>> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) >>>> Call Trace: >>>> ([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160) >>>> [<00000000008f15c4>] show_valid_zones+0x5c/0x190 >>>> [<00000000008cf9c4>] dev_attr_show+0x34/0x70 >>>> [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 >>>> [<00000000003e4194>] seq_read+0x204/0x480 >>>> [<00000000003b53ea>] __vfs_read+0x32/0x178 >>>> [<00000000003b55b2>] vfs_read+0x82/0x138 >>>> [<00000000003b5be2>] ksys_read+0x5a/0xb0 >>>> [<0000000000b86ba0>] system_call+0xdc/0x2d8 >>>> Last Breaking-Event-Address: >>>> [<0000000000385b26>] test_pages_in_a_zone+0xde/0x160 >>>> Kernel panic - not syncing: Fatal exception: panic_on_oops >>>> >>>> Fix the problem by initializing the last memory section of the highest zone >>>> in memmap_init_zone() till the very end, even if it goes beyond the zone >>>> end. >>> >>> Why do we need to restrict this to the highest zone? In other words, why >>> cannot we do what I was suggesting earlier [1]. What does prevent other >>> zones to have an incomplete section boundary? >>> >>> [1] http://lkml.kernel.org/r/20181105183533.GQ4361@dhcp22.suse.cz >>> >> >> I tried to go through the original list and make myself familiar with >> the bug. >> >> Confused why initialize the *last* end_pfn could fix this, since >> is_mem_section_removable() will iterate on each page of a section. This >> means we need to initialize all the pages left in the section. >That's exactly what the fix does. We initialize all the pages left in >the section. > You are right, I misunderstand your code. >> >> One way to fix this in my mind is to record the last pfn in mem_section. >Do you mean last initialized pfn? I guess we have agreed upon that the >entire section should be initialized. Well, that would be great. > >> This could be done in memory_preset(), since after that we may assume >> the section is full. Not sure whether you would like it. >> -- Wei Yang Help you, Help me