From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:56800 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2444122AbgJVI0S (ORCPT ); Thu, 22 Oct 2020 04:26:18 -0400 Date: Thu, 22 Oct 2020 10:26:54 +0200 From: Greg KH Subject: Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c" Message-ID: <20201022082654.GA1477657@kroah.com> References: <20200925045146.1283714-1-hch@lst.de> <20200925045146.1283714-3-hch@lst.de> <20201021161301.GA1196312@kroah.com> <20201021233914.GR3576660@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201021233914.GR3576660@ZenIV.linux.org.uk> List-ID: To: Al Viro , Nick Desaulniers Cc: Christoph Hellwig , kernel-team@android.com, Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , David Laight , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org On Thu, Oct 22, 2020 at 12:39:14AM +0100, Al Viro wrote: > On Wed, Oct 21, 2020 at 06:13:01PM +0200, Greg KH wrote: > > On Fri, Sep 25, 2020 at 06:51:39AM +0200, Christoph Hellwig wrote: > > > From: David Laight > > > > > > This lets the compiler inline it into import_iovec() generating > > > much better code. > > > > > > Signed-off-by: David Laight > > > Signed-off-by: Christoph Hellwig > > > --- > > > fs/read_write.c | 179 ------------------------------------------------ > > > lib/iov_iter.c | 176 +++++++++++++++++++++++++++++++++++++++++++++++ > > > 2 files changed, 176 insertions(+), 179 deletions(-) > > > > Strangely, this commit causes a regression in Linus's tree right now. > > > > I can't really figure out what the regression is, only that this commit > > triggers a "large Android system binary" from working properly. There's > > no kernel log messages anywhere, and I don't have any way to strace the > > thing in the testing framework, so any hints that people can provide > > would be most appreciated. > > It's a pure move - modulo changed line breaks in the argument lists > the functions involved are identical before and after that (just checked > that directly, by checking out the trees before and after, extracting two > functions in question from fs/read_write.c and lib/iov_iter.c (before and > after, resp.) and checking the diff between those. > > How certain is your bisection? The bisection is very reproducable. But, this looks now to be a compiler bug. I'm using the latest version of clang and if I put "noinline" at the front of the function, everything works. Nick, any ideas here as to who I should report this to? I'll work on a fixup patch for the Android kernel tree to see if I can work around it there, but others will hit this in Linus's tree sooner or later... thanks, greg k-h