Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753338AbaBDGz5 (ORCPT ); Tue, 4 Feb 2014 01:55:57 -0500 Received: from mail.parknet.co.jp ([210.171.160.6]:50508 "EHLO mail.parknet.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752931AbaBDGzq (ORCPT ); Tue, 4 Feb 2014 01:55:46 -0500 From: OGAWA Hirofumi To: Namjae Jeon Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Namjae Jeon , Amit Sahrawat Subject: Re: [PATCH v3 5/6] fat: permit to return phy block number by fibmap in fallocated region References: <1387953112-2828-1-git-send-email-linkinjeon@gmail.com> <87eh3kx1n6.fsf@devron.myhome.or.jp> <87a9e7wq6w.fsf@devron.myhome.or.jp> Date: Tue, 04 Feb 2014 15:55:37 +0900 In-Reply-To: (Namjae Jeon's message of "Tue, 4 Feb 2014 13:03:16 +0900") Message-ID: <8761ovwemu.fsf@devron.myhome.or.jp> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Namjae Jeon writes: > 2014-02-04, OGAWA Hirofumi : >> Namjae Jeon writes: >> >>>>> /* fat_get_cluster() assumes the requested blocknr isn't truncated. >>>>> */ >>>>> down_read(&MSDOS_I(mapping->host)->truncate_lock); >>>>> + /* To get block number beyond file size in fallocated region */ >>>>> + atomic_set(&MSDOS_I(mapping->host)->beyond_isize, 1); >>>>> blocknr = generic_block_bmap(mapping, block, fat_get_block); >>>>> + atomic_set(&MSDOS_I(mapping->host)->beyond_isize, 0); >>>>> up_read(&MSDOS_I(mapping->host)->truncate_lock); >>>> >>>> This is racy. While user is using bmap, kernel can allocate new blocks. >>>> We should use another function for this. >>> I understand that fat can map fallocated blocks in read case while >>> user is using bmap. >>> But I can not find the case allocate new blocks. >>> If I am missing something, Could you please elaborate more ? >>> Is it a case of _bmap request returning the block number for block >>> allocated in parallel write path ? >> >> ->beyond_size is global for inode. So, write(2) path on same inode with >> bmap() also can see 1 set by bmap() while another process is using bmap(). > 'create' flag will be 1 in write(2) path. ->beyond_isize will only be > checked when 'create' flag is 0. Is there any case to be racy by > beyond_isize in write(2) path ? Ah, so instead of write, it will assign physical address to buffers beyond i_size for simple read if race? In this case, it is still wrong. -- OGAWA Hirofumi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/