From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43072) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVFoD-0008Om-So for qemu-devel@nongnu.org; Wed, 12 Jul 2017 07:27:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVFo9-0000PI-TS for qemu-devel@nongnu.org; Wed, 12 Jul 2017 07:27:57 -0400 Received: from 9.mo68.mail-out.ovh.net ([46.105.78.111]:56996) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dVFo9-0000Ox-Jl for qemu-devel@nongnu.org; Wed, 12 Jul 2017 07:27:53 -0400 Received: from player750.ha.ovh.net (b6.ovh.net [213.186.33.56]) by mo68.mail-out.ovh.net (Postfix) with ESMTP id 23F726BFAD for ; Wed, 12 Jul 2017 13:27:52 +0200 (CEST) Date: Wed, 12 Jul 2017 13:27:42 +0200 From: Greg Kurz Message-ID: <20170712132742.368db8d8@bahia.lan> In-Reply-To: <20170712110545.GN4083@umbus.fritz.box> References: <20170712055317.26225-1-david@gibson.dropbear.id.au> <20170712055317.26225-3-david@gibson.dropbear.id.au> <20170712120001.31d858de@bahia.lan> <20170712110545.GN4083@umbus.fritz.box> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/fg8duMMSRFiv+k9/UYSTA+t"; protocol="application/pgp-signature" Subject: Re: [Qemu-devel] [PATCHv2 2/8] spapr: Remove 'awaiting_allocation' DRC flag List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: mdroth@linux.vnet.ibm.com, danielhb@linux.vnet.ibm.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org, lvivier@redhat.com, sjitindarsingh@gmail.com, bharata@linux.vnet.ibm.com --Sig_/fg8duMMSRFiv+k9/UYSTA+t Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Wed, 12 Jul 2017 21:05:45 +1000 David Gibson wrote: > On Wed, Jul 12, 2017 at 12:00:01PM +0200, Greg Kurz wrote: > > On Wed, 12 Jul 2017 15:53:11 +1000 > > David Gibson wrote: > > =20 > > > The awaiting_allocation flag in the DRC was introduced by aab9913 > > > "spapr_drc: Prevent detach racing against attach for CPU DR", alleged= ly to > > > prevent a guest crash on racing attach and detach. Except.. informat= ion > > > from the BZ actually suggests a qemu crash, not a guest crash. And t= here =20 > >=20 > > Can you share an url to the BZ ? =20 >=20 > Alas, no. I have that information second hand from.. Bharata, > think.. and I believe the BZ is an IBM internal one. >=20 I did some digging and I could find it in our internal bugzilla. And indeed, it mentions QEMU crashing because of a SEGV... > > =20 > > > shouldn't be a problem here anyway: if the guest has already moved th= e DRC > > > away from UNUSABLE state, the detach would already be deferred, and i= f it > > > hadn't it should be safe to detach it (the guest should fail graceful= ly > > > when it attempts to change the allocation state). > > >=20 > > > I think this was probably just a bandaid for some other problem in the > > > state management. So, remove awaiting_allocation and associated code. > > >=20 ... so I tend to agree this was a bandaid. Reviewed-by: Greg Kurz I'll re-try the scenario from the BZ with this patch applied to see if we hit the crash again. > > > Signed-off-by: David Gibson > > > --- > > > hw/ppc/spapr_drc.c | 25 +++---------------------- > > > include/hw/ppc/spapr_drc.h | 1 - > > > 2 files changed, 3 insertions(+), 23 deletions(-) > > >=20 > > > diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c > > > index 9b07f80..89ba3d6 100644 > > > --- a/hw/ppc/spapr_drc.c > > > +++ b/hw/ppc/spapr_drc.c > > > @@ -170,19 +170,13 @@ static uint32_t drc_set_usable(sPAPRDRConnector= *drc) > > > if (!drc->dev) { > > > return RTAS_OUT_NO_SUCH_INDICATOR; > > > } > > > - if (drc->awaiting_release && drc->awaiting_allocation) { > > > - /* kernel is acknowledging a previous hotplug event > > > - * while we are already removing it. > > > - * it's safe to ignore awaiting_allocation here since we kno= w the > > > - * situation is predicated on the guest either already havin= g done > > > - * so (boot-time hotplug), or never being able to acquire in= the > > > - * first place (hotplug followed by immediate unplug). > > > - */ > > > + if (drc->awaiting_release) { > > > + /* Don't allow the guest to move a device away from UNUSABLE > > > + * state when we want to unplug it */ > > > return RTAS_OUT_NO_SUCH_INDICATOR; > > > } > > > =20 > > > drc->allocation_state =3D SPAPR_DR_ALLOCATION_STATE_USABLE; > > > - drc->awaiting_allocation =3D false; > > > =20 > > > return RTAS_OUT_SUCCESS; > > > } > > > @@ -357,10 +351,6 @@ void spapr_drc_attach(sPAPRDRConnector *drc, Dev= iceState *d, void *fdt, > > > drc->fdt =3D fdt; > > > drc->fdt_start_offset =3D fdt_start_offset; > > > =20 > > > - if (spapr_drc_type(drc) !=3D SPAPR_DR_CONNECTOR_TYPE_PCI) { > > > - drc->awaiting_allocation =3D true; > > > - } > > > - > > > object_property_add_link(OBJECT(drc), "device", > > > object_get_typename(OBJECT(drc->dev)), > > > (Object **)(&drc->dev), > > > @@ -398,12 +388,6 @@ void spapr_drc_detach(sPAPRDRConnector *drc, Dev= iceState *d, Error **errp) > > > return; > > > } > > > =20 > > > - if (drc->awaiting_allocation) { > > > - drc->awaiting_release =3D true; > > > - trace_spapr_drc_awaiting_allocation(spapr_drc_index(drc)); > > > - return; > > > - } > > > - > > > spapr_drc_release(drc); > > > } > > > =20 > > > @@ -426,8 +410,6 @@ void spapr_drc_reset(sPAPRDRConnector *drc) > > > spapr_drc_release(drc); > > > } > > > =20 > > > - drc->awaiting_allocation =3D false; > > > - > > > if (drc->dev) { > > > /* A device present at reset is coldplugged */ > > > drc->isolation_state =3D SPAPR_DR_ISOLATION_STATE_UNISOLATED; > > > @@ -493,7 +475,6 @@ static const VMStateDescription vmstate_spapr_drc= =3D { > > > VMSTATE_UINT32(dr_indicator, sPAPRDRConnector), > > > VMSTATE_BOOL(configured, sPAPRDRConnector), > > > VMSTATE_BOOL(awaiting_release, sPAPRDRConnector), > > > - VMSTATE_BOOL(awaiting_allocation, sPAPRDRConnector), > > > VMSTATE_END_OF_LIST() > > > } > > > }; > > > diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h > > > index 715016b..18a196e 100644 > > > --- a/include/hw/ppc/spapr_drc.h > > > +++ b/include/hw/ppc/spapr_drc.h > > > @@ -200,7 +200,6 @@ typedef struct sPAPRDRConnector { > > > sPAPRConfigureConnectorState *ccs; > > > =20 > > > bool awaiting_release; > > > - bool awaiting_allocation; > > > =20 > > > /* device pointer, via link property */ > > > DeviceState *dev; =20 > > =20 >=20 >=20 >=20 --Sig_/fg8duMMSRFiv+k9/UYSTA+t Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iEYEARECAAYFAllmB64ACgkQAvw66wEB28JZbQCfVzDeR5rFCXGUDLrb0lPMvyML RkQAnRacw3WZUHHNz/3LbuyEcV4C4zDQ =eN1L -----END PGP SIGNATURE----- --Sig_/fg8duMMSRFiv+k9/UYSTA+t--