From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760764Ab3LILTO (ORCPT ); Mon, 9 Dec 2013 06:19:14 -0500 Received: from mail-pd0-f179.google.com ([209.85.192.179]:45607 "EHLO mail-pd0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753358Ab3LILTM (ORCPT ); Mon, 9 Dec 2013 06:19:12 -0500 Message-ID: <52A5A7B5.2040904@gmail.com> Date: Mon, 09 Dec 2013 19:21:25 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: James Hogan CC: Seth Jennings , linux-mm@kvack.org, "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm/zswap.c: add BUG() for default case in zswap_writeback_entry() References: <52A53024.9090701@gmail.com> <52A5935A.4040709@imgtec.com> <52A5973A.7020509@gmail.com> <52A5990E.2080808@imgtec.com> In-Reply-To: <52A5990E.2080808@imgtec.com> Content-Type: multipart/mixed; boundary="------------090306010206020002090309" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------090306010206020002090309 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit On 12/09/2013 06:18 PM, James Hogan wrote: > On 09/12/13 10:11, Chen Gang wrote: >>> Since the metag compiler is stuck on an old version (gcc 4.2.4), which >>> is wrong to warn in this case, and newer versions of gcc don't appear to >>> warn about it anyway (I just checked with gcc 4.7.2 x86_64), I have no >>> objection to this warning remaining in the metag build. >>> >> >> Do you try "EXTRA_CFLAGS=-W" with gcc 4.7.2? I guess it will report the >> warning too, I don't feel the compiler is smart enough (except it lets >> the long function zswap_get_swap_cache_page really inline) :-) > > EXTRA_CFLAGS=-W on gcc 4.7.2 gives me plenty of pointless unused > parameter warnings when compiling mm/zswap.o, but not the warning you're > trying to silence. > Yeah, it will generate plenty of pointless warnings, although we still can often find valuable bugs in these warnings. Oh, I tried gcc 4.6.3-2 rhel version, get the same result as yours (do not report warning), but for me, it is still a compiler's bug, it *should* report a warning for it, we can try below: - modify zswap_get_swap_cache_page() to let it may return another value (one sample modification is in attachment) - compile again, it doesn't report related warning, either - in this case, it *should* report related warning. Could you help to try it under gcc 4.7.2, thanks? BTW: gcc really exists some bugs about uninitialized variable, e.g. one known bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18501 kernel related: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57856 Thanks. -- Chen Gang Open, share, and attitude like air, water and life which God blessed --------------090306010206020002090309 Content-Type: text/x-patch; name="diff.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="diff.patch" diff --git a/mm/zswap.c b/mm/zswap.c index 5a63f78..1853ef4 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -469,8 +469,7 @@ static int zswap_get_swap_cache_page(swp_entry_t entry, */ err = radix_tree_preload(GFP_KERNEL); if (err) - break; - + return -4; /* * Swap entry may have been freed since our caller observed it. */ --------------090306010206020002090309--