From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 485E16B0253 for ; Thu, 18 Jan 2018 11:56:35 -0500 (EST) Received: by mail-wm0-f71.google.com with SMTP id h17so6667755wmc.6 for ; Thu, 18 Jan 2018 08:56:35 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id r1sor4984218edc.30.2018.01.18.08.56.33 for (Google Transport Security); Thu, 18 Jan 2018 08:56:33 -0800 (PST) Date: Thu, 18 Jan 2018 19:56:30 +0300 From: "Kirill A. Shutemov" Subject: Re: [mm 4.15-rc8] Random oopses under memory pressure. Message-ID: <20180118165629.kpdkezarsf4qymnw@node.shutemov.name> References: <201801160115.w0G1FOIG057203@www262.sakura.ne.jp> <201801170233.JDG21842.OFOJMQSHtOFFLV@I-love.SAKURA.ne.jp> <201801172008.CHH39543.FFtMHOOVSQJLFO@I-love.SAKURA.ne.jp> <201801181712.BFD13039.LtHOSVMFJQFOFO@I-love.SAKURA.ne.jp> <20180118122550.2lhsjx7hg5drcjo4@node.shutemov.name> <20180118145830.GA6406@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180118145830.GA6406@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Arcangeli Cc: Dave Hansen , Tetsuo Handa , torvalds@linux-foundation.org, kirill.shutemov@linux.intel.com, akpm@linux-foundation.org, hannes@cmpxchg.org, iamjoonsoo.kim@lge.com, mgorman@techsingularity.net, tony.luck@intel.com, vbabka@suse.cz, mhocko@kernel.org, hillf.zj@alibaba-inc.com, hughd@google.com, oleg@redhat.com, peterz@infradead.org, riel@redhat.com, srikar@linux.vnet.ibm.com, vdavydov.dev@gmail.com, mingo@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org On Thu, Jan 18, 2018 at 03:58:30PM +0100, Andrea Arcangeli wrote: > On Thu, Jan 18, 2018 at 06:45:00AM -0800, Dave Hansen wrote: > > On 01/18/2018 04:25 AM, Kirill A. Shutemov wrote: > > > [ 10.084024] diff: -858690919 > > > [ 10.084258] hpage_nr_pages: 1 > > > [ 10.084386] check1: 0 > > > [ 10.084478] check2: 0 > > ... > > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > > > index d22b84310f6d..57b4397f1ea5 100644 > > > --- a/mm/page_vma_mapped.c > > > +++ b/mm/page_vma_mapped.c > > > @@ -70,6 +70,14 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw) > > > } > > > if (pte_page(*pvmw->pte) < pvmw->page) > > > return false; > > > + > > > + if (pte_page(*pvmw->pte) - pvmw->page) { > > > + printk("diff: %d\n", pte_page(*pvmw->pte) - pvmw->page); > > > + printk("hpage_nr_pages: %d\n", hpage_nr_pages(pvmw->page)); > > > + printk("check1: %d\n", pte_page(*pvmw->pte) - pvmw->page < 0); > > > + printk("check2: %d\n", pte_page(*pvmw->pte) - pvmw->page >= hpage_nr_pages(pvmw->page)); > > > + BUG(); > > > + } > > > > This says that pte_page(*pvmw->pte) and pvmw->page are roughly 4GB away > > from each other (858690919*4=0xccba559c0). That's not the compiler > > being wonky, it just means that the virtual addresses of the memory > > sections are that far apart. > > > > This won't happen when you have vmemmap or flatmem because the mem_map[] > > is virtually contiguous and pointer arithmetic just works against all > > 'struct page' pointers. But with classic sparsemem, it doesn't. > > > > You need to make sure that the PFNs are in the same section before you > > can do the math that you want to do here. > > Isn't it simply that pvmw->page isn't a page or pte_page(*pvmw->pte) > isn't a page? > > The distance cannot matter, MMU isn't involved, this is pure 64bit > aritmetics, 1giga 1 terabyte, 48bits 5level pagetables are meaningless > in this comparison. Note, it's 32-bit. > > #include > > int main() > { > volatile long i; > struct x { char a[4000000000]; }; > for (i = 0; i < 4000000000*3; i += 4000000000) { > printf("%ld\n", ((struct x *)0)-((((struct x *)i)))); > } > printf("xxxx\n"); > for (i = 0; i < 4000000000; i += 1) { > if (i==4) > i = 4000000000; > printf("%ld\n", ((struct x *)0)-((((struct x *)i)))); > } > return 0; > } > > You need to add two debug checks on "pte_page(*pvmw->pte) % 64" and > same for pvmw->page to find out the one of the two that isn't a page. > > If both are real pages there's a bug that allocates page structs not > naturally aligned. Both are real page. But why do you expect pages to be 64-byte alinged? Both are aligned to 64-bit as they suppose to be IIUC. I can't say I fully grasp how 'diff' got this value and how it leads to both checks being false. [ 10.209657] page:f6e4cc38 count:8 mapcount:6 mapping:f5818f94 index:0x0 [ 10.209989] flags: 0x3501004d(locked|referenced|uptodate|active|mappedtodisk) [ 10.210496] raw: 3501004d f5818f94 00000000 00000005 00000008 00000100 00000200 00000000 [ 10.210742] raw: f5c06600 00000000 [ 10.210863] page dumped because: pvmw->page [ 10.210992] page->mem_cgroup:f5c06600 [ 10.211192] page:f74749d8 count:1 mapcount:1 mapping:f54612d1 index:0x0 [ 10.211381] flags: 0x15040068(uptodate|lru|active|swapbacked) [ 10.211530] raw: 15040068 f54612d1 00000000 00000000 00000001 f74749c4 f75b9014 00000000 [ 10.211729] raw: f5c06600 00000000 [ 10.211806] page dumped because: pte_page(*pvmw->pte) [ 10.211920] page->mem_cgroup:f5c06600 [ 10.212079] diff: -858832092 [ 10.212184] hpage_nr_pages: 1 [ 10.212284] check1: 0 [ 10.212384] check2: 0 -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org