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Violators will be prosecuted for from ; Mon, 10 Dec 2018 16:14:35 -0000 Subject: Re: [PATCH 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section References: <20181210130712.30148-1-zaslonko@linux.ibm.com> <20181210130712.30148-2-zaslonko@linux.ibm.com> <20181210151005.xukiibwbb6ohqyex@master> From: Zaslonko Mikhail Date: Mon, 10 Dec 2018 17:14:36 +0100 MIME-Version: 1.0 In-Reply-To: <20181210151005.xukiibwbb6ohqyex@master> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: Wei Yang , Mikhail Zaslonko Cc: 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 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 > >> } >> >> #ifdef CONFIG_ZONE_DEVICE >> -- >> 2.16.4 > Thanks, Mikhail Zaslonko