Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F673C6FD1D for ; Mon, 20 Mar 2023 11:21:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229885AbjCTLVU (ORCPT ); Mon, 20 Mar 2023 07:21:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45638 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229810AbjCTLU4 (ORCPT ); Mon, 20 Mar 2023 07:20:56 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3AFA9A2; Mon, 20 Mar 2023 04:20:39 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 982421F86C; Mon, 20 Mar 2023 11:20:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1679311238; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=txOGnZ8/Pa5itReU7gFMvzIp1cdxXBCMH8CKi+tOGU4=; b=fVGfqRUEesqYmxQkLjSGwURYl8kf83Bhyqo6FTw/ZsE9N+UI2mQs6bR7vVnmyeqCaqU0Yb fxAM7tFXoZcwEZ7cR8F64w775iDYZOKwZchU8SxrFh6fLb3nrlc54e+IZr5uVk7gEM/YN2 oCIN+t4SRVBMAtiubQ+ajTKCrOhc7/A= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1679311238; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=txOGnZ8/Pa5itReU7gFMvzIp1cdxXBCMH8CKi+tOGU4=; b=9xOas0vAFYpzlxKucsUCTDzYGtpbMx4Szkl6TA04NsjqRgAEAnxBIOXdA5a+MWqABn5M6k fVX5BxGlisiAHdBQ== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 8A51813416; Mon, 20 Mar 2023 11:20:38 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id nhq2IYZBGGQXMgAAMHmgww (envelope-from ); Mon, 20 Mar 2023 11:20:38 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 18346A0719; Mon, 20 Mar 2023 12:20:38 +0100 (CET) Date: Mon, 20 Mar 2023 12:20:38 +0100 From: Jan Kara To: Zhihao Cheng Cc: Jan Kara , tytso@mit.edu, adilger.kernel@dilger.ca, jack@suse.com, tudor.ambarus@linaro.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com Subject: Re: [PATCH] ext4: Fix i_disksize exceeding i_size problem in paritally written case Message-ID: <20230320112038.3q2eqpv6xsmj22br@quack3> References: <20230317013553.1009553-1-chengzhihao1@huawei.com> <20230317124513.drx3wywcjnap5jme@quack3> <884950ac-e60a-d331-9f68-310ab81ee595@huawei.com> <71990726-c677-34df-d29b-a0fec1a6f68c@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <71990726-c677-34df-d29b-a0fec1a6f68c@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Sat 18-03-23 16:51:00, Zhihao Cheng wrote: > > Hi, Jan > > > On Fri 17-03-23 09:35:53, Zhihao Cheng wrote: > > > > Following process makes i_disksize exceed i_size: > > > > > > > > generic_perform_write > > > > ? copied = iov_iter_copy_from_user_atomic(len) // copied < len > > > > ? ext4_da_write_end > > > > ? | ext4_update_i_disksize > > > > ? |? new_i_size = pos + copied; > > > > ? |? WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize > > > > ? | generic_write_end > > > > ? |? copied = block_write_end(copied, len) // copied = 0 > > > > ? |?? if (unlikely(copied < len)) > > > > ? |??? if (!PageUptodate(page)) > > > > ? |???? copied = 0; > > > > ? |? if (pos + copied > inode->i_size) // return false > > > > ? if (unlikely(copied == 0)) > > > > ?? goto again; > > > > ? if (unlikely(iov_iter_fault_in_readable(i, bytes))) { > > > > ?? status = -EFAULT; > > > > ?? break; > > > > ? } > > > > > > > > We get i_disksize greater than i_size here, which could trigger WARNING > > > > check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio: > > > > > > > > ext4_dio_write_iter > > > > ? iomap_dio_rw > > > > ?? __iomap_dio_rw // return err, length is not aligned to 512 > > > > ? ext4_handle_inode_extension > > > > ?? WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops > > > > > > > > ? WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319 > > > > ? CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2 > > > > ? RIP: 0010:ext4_file_write_iter+0xbc7 > > > > ? Call Trace: > > > > ?? vfs_write+0x3b1 > > > > ?? ksys_write+0x77 > > > > ?? do_syscall_64+0x39 > > > > > > > > Fix it by putting block_write_end() before i_disksize updating just > > > > like ext4_write_end() does. > > > > > > > > Fetch a reproducer in [Link]. > > > > > > > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209 > > > > Fixes: 64769240bd07f ("ext4: Add delayed allocation support in > > > > data=writeback mode") > > > > Signed-off-by: Zhihao Cheng > > > > > > Good catch (although practically this will hardly have any negative > > > effect). But rather than opencoding generic_write_end() I'd do: > > > > > > ???????? if (unlikely(copied < len) && !PageUptodate(page)) > > > ???????????????? copied = 0; > > > > > > at the beginning of ext4_da_write_end() and that should solve these > > > problems as well? > > > > > > > Yes, your suggestion looks good, and I think we can put the checking > > just after ext4_write_inline_data_end(Line 3150)? On the one hand, we > > can pass original 'copied' value in trace_ext4_da_write_end(), one the > > other hand, ext4_write_inline_data_end() already has this checking. > > . > > BTW, I want send another patch as follows: > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index bf0b7dea4900..570a687ae847 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file, > return ext4_write_inline_data_end(inode, pos, len, copied, > page); > > start = pos & (PAGE_SIZE - 1); > - end = start + copied - 1; > + end = start + (copied ? copied - 1 : copied); > > /* > * Since we are holding inode lock, we are sure i_disksize <= > @@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file, > * ext4_da_write_inline_data_end(). > */ > new_i_size = pos + copied; > - if (copied && new_i_size > inode->i_size && > + if (new_i_size > inode->i_size && > ext4_da_should_update_i_disksize(page, end)) > ext4_update_i_disksize(inode, new_i_size); > > This modification handle unconsistent i_size and i_disksize imported by > ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()"). > > Paritially written may display a fake inode size for user, for example: > > > > i_disksize=1 > > generic_perform_write > > copied = iov_iter_copy_from_user_atomic(len) // copied = 0 > > ext4_da_write_end // skip updating i_disksize > > generic_write_end > > if (pos + copied > inode->i_size) { // 10 + 0 > 1, true > > i_size_write(inode, pos + copied); // i_size = 10 > > } > > > > 0 1 10 4096 > > |_|_______|_________..._____| > > | | > > i_size pos > > > > Now, user see the i_size is 10 (i_disksize is still 1). After inode > > destroyed, user will get the i_size is 1 read from disk. OK, but shouldn't we rather change generic_write_end() to not increase i_size if no write happened? Because that is what seems somewhat problematic... Honza -- Jan Kara SUSE Labs, CR