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[209.85.220.65]) by mx.google.com with SMTPS id n19-v6sor3322290ejr.12.2018.12.10.17.50.13 for (Google Transport Security); Mon, 10 Dec 2018 17:50:13 -0800 (PST) Date: Tue, 11 Dec 2018 01:50:11 +0000 From: Wei Yang Subject: Re: [PATCH 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section Message-ID: <20181211015011.bcbugtm2v6j3ncpc@master> Reply-To: Wei Yang References: <20181210130712.30148-1-zaslonko@linux.ibm.com> <20181210130712.30148-2-zaslonko@linux.ibm.com> <20181210151005.xukiibwbb6ohqyex@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Zaslonko Mikhail Cc: Wei Yang , Mikhail Zaslonko , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, Pavel.Tatashin@microsoft.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, gerald.schaefer@de.ibm.com On Mon, Dec 10, 2018 at 05:14:36PM +0100, Zaslonko Mikhail wrote: >Hello, > >On 10.12.2018 16:10, Wei Yang wrote: >> On Mon, Dec 10, 2018 at 02:07:12PM +0100, 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. 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. >>> >>> Signed-off-by: Mikhail Zaslonko >>> Reviewed-by: Gerald Schaefer >>> Cc: >>> --- >>> mm/page_alloc.c | 15 +++++++++++++++ >>> 1 file changed, 15 insertions(+) >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index 2ec9cc407216..41ef5508e5f1 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -5542,6 +5542,21 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone, >>> cond_resched(); >>> } >>> } >>> +#ifdef CONFIG_SPARSEMEM >>> + /* >>> + * If there is no zone spanning the rest of the section >>> + * then we should at least initialize those pages. Otherwise we >>> + * could blow up on a poisoned page in some paths which depend >>> + * on full sections being initialized (e.g. memory hotplug). >>> + */ >>> + if (end_pfn == max_pfn) { >>> + while (end_pfn % PAGES_PER_SECTION) { >>> + __init_single_page(pfn_to_page(end_pfn), end_pfn, zone, >>> + nid); >>> + end_pfn++; >>> + } >>> + } >>> +#endif >> >> If my understanding is correct, end_pfn is not a valid range. >> >> memmap_init_zone() initialize the range [start_pfn, start_pfn + size). I >> am afraid this will break the syntax. >> >> And max_pfn is also not a valid one. For example, on x86, >I used pfn_max here to check for the highest zone. What would be a better way? > >> update_end_of_memory_vars() will update max_pfn, which is calculated by: >> >> end_pfn = PFN_UP(start + size); >> >> BTW, as you mentioned this apply to hotplug case. And then why this couldn't >> happen during boot up? What differ these two cases? > >Well, the pages left uninitialized during bootup (initial problem), but the panic itself takes >place when we try to process memory_hotplug sysfs attributes (thus triggering sysfs handlers). >You can find more details in the original thread: >https://marc.info/?t=153658306400001&r=1&w=2 > Thanks. I took a look into the original thread and try to reproduce this on x86. My step is: 1. config page_poisoning 2. use kernel parameter mem=3075M 3. cat the last memory block device sysfs file removable eg. when mem is 3075, cat memory9/removable I don't see the Call trace. Do I miss something to reproduce it? >> >>> } >>> >>> #ifdef CONFIG_ZONE_DEVICE >>> -- >>> 2.16.4 >> > >Thanks, >Mikhail Zaslonko -- Wei Yang Help you, Help me