Re: [PATCH] spapr: Don't request to unplug the same core twice
On Thu, Oct 24, 2019 at 08:28:54AM +0200, Greg Kurz wrote:
> On Thu, 24 Oct 2019 09:38:17 +1100
> David Gibson wrote:
>
> > On Wed, Oct 23, 2019 at 09:17:40PM +0200, Greg Kurz wrote:
> > > We must not call spapr_drc_detach() on a detached DRC otherwise bad things
> > > can happen, ie. QEMU hangs or crashes. This is easily demonstrated with
> > > a CPU hotplug/unplug loop using QMP.
> > >
> > > Signed-off-by: Greg Kurz
> >
> > Ouch, good catch. Applied.
> >
> > I wonder if we have the same problem with other DRC types.
> >
>
> We don't have it with PHB and PCI types, through the same use of
> spapr_drc_unplug_requested().
>
> LMBs see to avoid it by failing device_del early if an unplug
> request is already in progress:
>
> /*
> * An existing pending dimm state for this DIMM means that there is an
> * unplug operation in progress, waiting for the spapr_lmb_release
> * callback to complete the job (BQL can't cover that far). In this case,
> * bail out to avoid detaching DRCs that were already released.
> */
> if (spapr_pending_dimm_unplugs_find(spapr, dimm)) {
> error_setg(_err,
>"Memory unplug already in progress for device %s",
>dev->id);
> goto out;
> }
>
> Not sure why we error out in this case instead of ignoring the unplug
> request.
I suspect no particularly good reason, just history. Everything's a
bit different with LMBs because a single device_del will usually
remove a whole bunch of LMB DRCs. In general the interfacing between
the qemu user side DIMM handling and the PAPR side LMB/DRC handling
is... pretty clunky.
>
> > > ---
> > > hw/ppc/spapr.c |7 ---
> > > 1 file changed, 4 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index f9410d390a07..94f9d27096af 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -3741,9 +3741,10 @@ void spapr_core_unplug_request(HotplugHandler
> > > *hotplug_dev, DeviceState *dev,
> > >spapr_vcpu_id(spapr, cc->core_id));
> > > g_assert(drc);
> > >
> > > -spapr_drc_detach(drc);
> > > -
> > > -spapr_hotplug_req_remove_by_index(drc);
> > > +if (!spapr_drc_unplug_requested(drc)) {
> > > +spapr_drc_detach(drc);
> > > +spapr_hotplug_req_remove_by_index(drc);
> > > +}
> > > }
> > >
> > > int spapr_core_dt_populate(SpaprDrc *drc, SpaprMachineState *spapr,
> > >
> >
>
--
David Gibson| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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Re: [PATCH] spapr: Don't request to unplug the same core twice
On Thu, 24 Oct 2019 09:38:17 +1100
David Gibson wrote:
> On Wed, Oct 23, 2019 at 09:17:40PM +0200, Greg Kurz wrote:
> > We must not call spapr_drc_detach() on a detached DRC otherwise bad things
> > can happen, ie. QEMU hangs or crashes. This is easily demonstrated with
> > a CPU hotplug/unplug loop using QMP.
> >
> > Signed-off-by: Greg Kurz
>
> Ouch, good catch. Applied.
>
> I wonder if we have the same problem with other DRC types.
>
We don't have it with PHB and PCI types, through the same use of
spapr_drc_unplug_requested().
LMBs see to avoid it by failing device_del early if an unplug
request is already in progress:
/*
* An existing pending dimm state for this DIMM means that there is an
* unplug operation in progress, waiting for the spapr_lmb_release
* callback to complete the job (BQL can't cover that far). In this case,
* bail out to avoid detaching DRCs that were already released.
*/
if (spapr_pending_dimm_unplugs_find(spapr, dimm)) {
error_setg(_err,
"Memory unplug already in progress for device %s",
dev->id);
goto out;
}
Not sure why we error out in this case instead of ignoring the unplug
request.
> > ---
> > hw/ppc/spapr.c |7 ---
> > 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index f9410d390a07..94f9d27096af 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -3741,9 +3741,10 @@ void spapr_core_unplug_request(HotplugHandler
> > *hotplug_dev, DeviceState *dev,
> >spapr_vcpu_id(spapr, cc->core_id));
> > g_assert(drc);
> >
> > -spapr_drc_detach(drc);
> > -
> > -spapr_hotplug_req_remove_by_index(drc);
> > +if (!spapr_drc_unplug_requested(drc)) {
> > +spapr_drc_detach(drc);
> > +spapr_hotplug_req_remove_by_index(drc);
> > +}
> > }
> >
> > int spapr_core_dt_populate(SpaprDrc *drc, SpaprMachineState *spapr,
> >
>
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Re: [PATCH] spapr: Don't request to unplug the same core twice
On Wed, Oct 23, 2019 at 09:17:40PM +0200, Greg Kurz wrote:
> We must not call spapr_drc_detach() on a detached DRC otherwise bad things
> can happen, ie. QEMU hangs or crashes. This is easily demonstrated with
> a CPU hotplug/unplug loop using QMP.
>
> Signed-off-by: Greg Kurz
Ouch, good catch. Applied.
I wonder if we have the same problem with other DRC types.
> ---
> hw/ppc/spapr.c |7 ---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index f9410d390a07..94f9d27096af 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -3741,9 +3741,10 @@ void spapr_core_unplug_request(HotplugHandler
> *hotplug_dev, DeviceState *dev,
>spapr_vcpu_id(spapr, cc->core_id));
> g_assert(drc);
>
> -spapr_drc_detach(drc);
> -
> -spapr_hotplug_req_remove_by_index(drc);
> +if (!spapr_drc_unplug_requested(drc)) {
> +spapr_drc_detach(drc);
> +spapr_hotplug_req_remove_by_index(drc);
> +}
> }
>
> int spapr_core_dt_populate(SpaprDrc *drc, SpaprMachineState *spapr,
>
--
David Gibson| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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[PATCH] spapr: Don't request to unplug the same core twice
We must not call spapr_drc_detach() on a detached DRC otherwise bad things
can happen, ie. QEMU hangs or crashes. This is easily demonstrated with
a CPU hotplug/unplug loop using QMP.
Signed-off-by: Greg Kurz
---
hw/ppc/spapr.c |7 ---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index f9410d390a07..94f9d27096af 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -3741,9 +3741,10 @@ void spapr_core_unplug_request(HotplugHandler
*hotplug_dev, DeviceState *dev,
spapr_vcpu_id(spapr, cc->core_id));
g_assert(drc);
-spapr_drc_detach(drc);
-
-spapr_hotplug_req_remove_by_index(drc);
+if (!spapr_drc_unplug_requested(drc)) {
+spapr_drc_detach(drc);
+spapr_hotplug_req_remove_by_index(drc);
+}
}
int spapr_core_dt_populate(SpaprDrc *drc, SpaprMachineState *spapr,
