From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753085AbcEYGYl (ORCPT ); Wed, 25 May 2016 02:24:41 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:43860 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752245AbcEYGYk (ORCPT ); Wed, 25 May 2016 02:24:40 -0400 Date: Wed, 25 May 2016 07:24:34 +0100 From: Al Viro To: Matthew McClintock Cc: Larry Finger , LKML Subject: Re: Regression in 4.6.0-git - bisected to commit dd254f5a382c Message-ID: <20160525062434.GE14480@ZenIV.linux.org.uk> References: <57437683.30008@lwfinger.net> <20160524001854.GW14480@ZenIV.linux.org.uk> <57447CE1.9020207@lwfinger.net> <6E57F7A4-59B0-46EA-9FFF-D0A4BA2D8E51@codeaurora.org> <5744A899.70503@lwfinger.net> <3988EB49-F17D-452B-A1AD-F202265B1BCA@codeaurora.org> <5744AD31.4090808@lwfinger.net> <2D6D38D9-FE06-4115-8FB2-48CB2FB19809@codeaurora.org> <20160524234133.GA14480@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20160524234133.GA14480@ZenIV.linux.org.uk> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 25, 2016 at 12:41:33AM +0100, Al Viro wrote: > On Tue, May 24, 2016 at 05:31:51PM -0500, Matthew McClintock wrote: > > > > > On May 24, 2016, at 2:36 PM, Larry Finger wrote: > > > > > > On 05/24/2016 02:25 PM, Matthew McClintock wrote: > > >> On May 24, 2016, at 2:16 PM, Larry Finger wrote: > > >>> > > >>> On 05/24/2016 02:13 PM, Matthew McClintock wrote: > > >>>> I’m seeing this too, same commit if you want another person to test/reproduce. > > >>> > > >>> If you do a pull today, does that fix your problem? > > >> > > >> Hmm, no. Which commit am I looking for? I’m on a56f489502e28caac56c8a0735549740f0ae0711 > > > > > > Commit 84787c572d402644dca4874aba73324d9f8e3948 is working for me. I have a fixup in lib/iov_iter.c with a dump_stack() call if the fixup was needed. That dump is not triggered. I do not seem to have a56f489502e yet. > > > > Still seeing the issue on top of tree and the above commit. Re-ran bisection just to be sure. > > Guys, the bug is real and definitely still there. > char c; > struct iovec v[2] = {{&c, 0}, {&c, 1}}; > readv(0, v, 2); > will trigger it just fine with stdin on e.g. tty. It needs fixing and I'll > post a fix as soon as it gets through the local testing. In the meanwhile, > I would like to know what in userland is doing that kind of call - kernel > certainly shouldn't end up in an infinite loop on that, but it's bloody odd > and I wonder what's going on in userland code to result in that call. > > Again, I understand what's going on kernel-side; the only tricky part is how > to fix it without bringing the nasal daemons back. I think I have a solution > and I'm going to post it tonight if it survives the local beating. In any > case, the testcase above deserves being added to LTP - it's a real regression. FWIW, the reproducer is #include main() { char c; struct iovec v[2] = {{&c,0},{&c,1}}; readv(0, v, 2); } ran with stdin from tty. Fix for that is simply diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 28cb431..0cd5227 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -101,7 +101,7 @@ #define iterate_and_advance(i, n, v, I, B, K) { \ if (unlikely(i->count < n)) \ n = i->count; \ - if (n) { \ + if (i->count) { \ size_t skip = i->iov_offset; \ if (unlikely(i->type & ITER_BVEC)) { \ const struct bio_vec *bvec; \ Could you see if your reproducer is fixed by that?