From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754654AbcKBHKM (ORCPT ); Wed, 2 Nov 2016 03:10:12 -0400 Received: from [119.145.14.66] ([119.145.14.66]:57895 "EHLO szxga03-in.huawei.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1750786AbcKBHKL (ORCPT ); Wed, 2 Nov 2016 03:10:11 -0400 Subject: Re: [PATCH v2] f2fs: replace a build-time warning with runtime WARN_ON To: Arnd Bergmann , Jaegeuk Kim References: <20161027153256.4121871-1-arnd@arndb.de> CC: Fan Li , Weichao Guo , , From: Chao Yu Message-ID: Date: Wed, 2 Nov 2016 15:09:03 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <20161027153256.4121871-1-arnd@arndb.de> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Arnd, Jaegeuk, It is trivial, but it's better keep commit *title*, commit log and code consistent. :) Thanks, On 2016/10/27 23:32, Arnd Bergmann wrote: > gcc is unsure about the use of last_ofs_in_node, which might happen > without a prior initialization: > > fs/f2fs//git/arm-soc/fs/f2fs/data.c: In function ‘f2fs_map_blocks’: > fs/f2fs/data.c:799:54: warning: ‘last_ofs_in_node’ may be used uninitialized in this function [-Wmaybe-uninitialized] > if (prealloc && dn.ofs_in_node != last_ofs_in_node + 1) { > > As pointed out by Chao Yu, the code is actually correct as 'prealloc' > is only set if the last_ofs_in_node has been set, the two always > get updated together. > > This initializes last_ofs_in_node to dn.ofs_in_node for each > new dnode at the start of the 'next_block' loop, which at that > point is a correct initialization as well. I assume that compilers > that correctly track the contents of the variables and do not > warn about the condition also figure out that they can eliminate > the extra assignment here. > > Fixes: 46008c6d4232 ("f2fs: support in batch multi blocks preallocation") > Signed-off-by: Arnd Bergmann > --- > fs/f2fs/data.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > v2: use simpler workaround, as discussed with Chao Yu. > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c > index 68edb47f5f71..cf5ec39f907d 100644 > --- a/fs/f2fs/data.c > +++ b/fs/f2fs/data.c > @@ -713,7 +713,7 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, > } > > prealloc = 0; > - ofs_in_node = dn.ofs_in_node; > + last_ofs_in_node = ofs_in_node = dn.ofs_in_node; > end_offset = ADDRS_PER_PAGE(dn.node_page, inode); > > next_block: >