From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from zimbra13.linbit.com (zimbra.linbit.com [212.69.161.123]) by mail09.linbit.com (LINBIT Mail Daemon) with ESMTP id 1876D101AC7E for ; Wed, 24 Sep 2014 12:04:45 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by zimbra13.linbit.com (Postfix) with ESMTP id 0C2332A0C2F for ; Wed, 24 Sep 2014 12:04:45 +0200 (CEST) Received: from zimbra13.linbit.com ([127.0.0.1]) by localhost (zimbra13.linbit.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id takVhiVl4hgw for ; Wed, 24 Sep 2014 12:04:44 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by zimbra13.linbit.com (Postfix) with ESMTP id E236F2A5795 for ; Wed, 24 Sep 2014 12:04:44 +0200 (CEST) Received: from zimbra13.linbit.com ([127.0.0.1]) by localhost (zimbra13.linbit.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id Bfic6AfTpaX0 for ; Wed, 24 Sep 2014 12:04:44 +0200 (CEST) Received: from soda.linbit (tuerlsteher.linbit.com [86.59.100.100]) by zimbra13.linbit.com (Postfix) with ESMTPS id 36A682A0C2F for ; Wed, 24 Sep 2014 12:04:44 +0200 (CEST) Date: Wed, 24 Sep 2014 12:04:42 +0200 From: Lars Ellenberg To: drbd-dev@lists.linbit.com Message-ID: <20140924100442.GB7118@soda.linbit> References: <20140919094909.GA21578@schiffbauer.net> <20140919144805.GS13125@soda.linbit> <20140919151653.GH21578@schiffbauer.net> <20140923110348.GA19076@soda.linbit> <20140923170824.GA32597@schiffbauer.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20140923170824.GA32597@schiffbauer.net> Content-Transfer-Encoding: quoted-printable Subject: Re: [Drbd-dev] drbd 8.4.3: refcounter overflow on re-sync List-Id: "*Coordination* of development, patches, contributions -- *Questions* \(even to developers\) go to drbd-user, please." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Sep 23, 2014 at 07:08:24PM +0200, Marc Schiffbauer wrote: > * Lars Ellenberg schrieb am 23.09.14 um 13:03 Uhr: > >On Fri, Sep 19, 2014 at 05:16:53PM +0200, Marc Schiffbauer wrote: > >>* Lars Ellenberg schrieb am 19.09.14 um 16:48 Uhr: > >>>On Fri, Sep 19, 2014 at 11:49:09AM +0200, Marc Schiffbauer wrote: > >>>>Hi, > >>>> > >>> > >>>If you resolve that to a code line, > >>>I may be able to figure out what PAX is talking about. > >>> > >>>But from this stack trace alone, I have absolutely no idea what PAX > >>>is trying to say, which refcount could possibly be meant there, > >>>let alone why it could possibly overflow or. > >>> > >>>Ah, ok. Looking at [1], "PaX Team" says: > >>>.--- > >>>| after having looked at the drbd code a bit i think this could be a > >>>| real bug in drbd but only upstream can tell for sure so you'll hav= e to > >>>| contact them. you can show them the following that i figured out s= o far: > >>>| > >>>| the refcount overflow was detected in > >>>| drivers/block/drbd/drbd_bitmap.c:bm_page_io_async at the > >>>| > >>>| atomic_add(len >> 9, &mdev->rs_sect_ev) > >>> > >>>Well, yes, why would it not overflow. > >>>It is *not* a refcount. > >>>It is an atomic counter. > >>>It is meant to overflow. > >> > >>Ok, then I can report this back and it should be fixed in PaX as a > >>false postive. Thanks for clarifying this. > > > >I still don't get why PAX is even sending a signal there. > >How could sending a signal possibly help against an overflowing counte= r? >=20 >=20 > PAX is a patchset for the linux kernel that hardens the kernel in > several ways. >=20 > The REFCOUNT feature will detect and prevent overflowing of > refcounters. >=20 > This is a good introduction of what it does: > http://wiki.gentoo.org/wiki/Hardened/PaX_Quickstart Yeah. Why would sending a signal to the current thread prevent a counter from overflowing. How could that possibly improve the overall situation, even assuming that the overflow would have bad side effects? Never mind. This won't be a fruitful discussion... --=20 : Lars Ellenberg : LINBIT | Your Way to High Availability : DRBD/HA support and consulting http://www.linbit.com DRBD=AE and LINBIT=AE are registered trademarks of LINBIT, Austria.