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Violators will be prosecuted for from ; Tue, 11 Dec 2018 15:23:15 -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> <20181211015011.bcbugtm2v6j3ncpc@master> From: Zaslonko Mikhail Date: Tue, 11 Dec 2018 16:23:05 +0100 MIME-Version: 1.0 In-Reply-To: <20181211015011.bcbugtm2v6j3ncpc@master> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: <3dbbb746-d4b4-ea17-643a-5d63d4f7e239@linux.bm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wei Yang Cc: 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 Hello, On 11.12.2018 02:50, Wei Yang wrote: > 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? > No you don't. I guess there might be deviations depending on the architecture (I am on s390). As I understand, memory block size is 384 Mb on your system and memory9 is the last block on the list? BTW, do you have CONFIG_DEBUG_VM and CONFIG_DEBUG_VM_PGFLAGS on? >>> >>>> } >>>> >>>> #ifdef CONFIG_ZONE_DEVICE >>>> -- >>>> 2.16.4 >>> >> >> Thanks, >> Mikhail Zaslonko >