Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932675AbdHWUNH (ORCPT ); Wed, 23 Aug 2017 16:13:07 -0400 Received: from mail-oi0-f45.google.com ([209.85.218.45]:35230 "EHLO mail-oi0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932603AbdHWUNF (ORCPT ); Wed, 23 Aug 2017 16:13:05 -0400 MIME-Version: 1.0 In-Reply-To: References: <1ae53e17-e455-4f17-0280-b0dae183a449@nazar.ca> From: Linus Torvalds Date: Wed, 23 Aug 2017 13:13:04 -0700 X-Google-Sender-Auth: ZNetPhCO6gBzWe5qSopn7EeQPtY Message-ID: Subject: Re: Kernels v4.9+ cause short reads of block devices To: Doug Nazar Cc: Al Viro , Linux Kernel Mailing List , Wei Fang , linux-fsdevel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1640 Lines: 44 On Wed, Aug 23, 2017 at 12:53 PM, Doug Nazar wrote: > > It's compiling now, but I think it's already set to MAX_LFS_FILESIZE. > > [ 169.095127] ppos=80180006000, s_maxbytes=7ffffffffff, magic=0x62646576, > type=bdev Oh, right you are - I'm much too used to 64-bit, where MAX_LFS_FILESIZE is basically infinite, and was jusr assuming that it was something like the UFS bug we had not that long ago that was due to the 32-bit limit. But yes, on 32-bit, we are limited by the 32-bit index into the page cache, and we limit the index to 31 bits too, so we have (PAGE_SIZE << 31) -1, which is that 7ffffffffff. And that also explains why people haven't seen it. You do need (a) 32-bit environment (b) a disk larger than that 8TB in size The *hard* limit for the page cache on a 32-bit environment should actually be (PAGE_SIZE << 32)-PAGE_SIZE (that final PAGE_SIZE subtraction is to make sure we don't generate that page cache with index -1), so having a disk that is 16TB or larger is not going to work, but your disk is right in that 8TB-16TB hole that used to work and was broken by that check. Anyway, that makes me feel better. I should have looked at your disk size more, now I at least understand why nobody noticed before. So just throw away my patch. That's wrong, and garbage. The *right* patch is likely to just this instead: -#define MAX_LFS_FILESIZE (((loff_t)PAGE_SIZE << (BITS_PER_LONG-1))-1) +#define MAX_LFS_FILESIZE (((loff_t)PAGE_SIZE << BITS_PER_LONG)-PAGE_SIZE) which should make MAX_LFS_FILESIZE be 0xffffffff000 and you disk size should be ok. Linus