Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753257AbaBDHAW (ORCPT ); Tue, 4 Feb 2014 02:00:22 -0500 Received: from mail-qc0-f181.google.com ([209.85.216.181]:46789 "EHLO mail-qc0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752157AbaBDHAS (ORCPT ); Tue, 4 Feb 2014 02:00:18 -0500 MIME-Version: 1.0 In-Reply-To: <8761ovwemu.fsf@devron.myhome.or.jp> References: <1387953112-2828-1-git-send-email-linkinjeon@gmail.com> <87eh3kx1n6.fsf@devron.myhome.or.jp> <87a9e7wq6w.fsf@devron.myhome.or.jp> <8761ovwemu.fsf@devron.myhome.or.jp> Date: Tue, 4 Feb 2014 16:00:17 +0900 Message-ID: Subject: Re: [PATCH v3 5/6] fat: permit to return phy block number by fibmap in fallocated region From: Namjae Jeon To: OGAWA Hirofumi Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Namjae Jeon , Amit Sahrawat Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2014-02-04, OGAWA Hirofumi : > 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. Right. I will fix this case. Thanks for review! > -- > 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/