pci: Add missing drop of bus master AS reference

[Qemu-devel] [PATCH qemu] pci: Add missing drop of bus master AS reference

Posted by Alexey Kardashevskiy 7 years ago

The recent introduction of a bus master container added
memory_region_add_subregion() into the PCI device registering path but
missed memory_region_del_subregion() in the unregistering path leaving
a reference to the root memory region of the new container.

This adds missing memory_region_del_subregion().

Fixes: 3716d5902d743 ("pci: introduce a bus master container")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 hw/pci/pci.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index e6b08e1988..bd8043c460 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -869,6 +869,8 @@ static void do_pci_unregister_device(PCIDevice *pci_dev)
     pci_dev->bus->devices[pci_dev->devfn] = NULL;
     pci_config_free(pci_dev);
 
+    memory_region_del_subregion(&pci_dev->bus_master_container_region,
+                                &pci_dev->bus_master_enable_region);
     address_space_destroy(&pci_dev->bus_master_as);
 }
 
-- 
2.11.0

Re: [Qemu-devel] [PATCH qemu] pci: Add missing drop of bus master AS reference

Posted by Paolo Bonzini 7 years ago


On 27/03/2017 06:40, Alexey Kardashevskiy wrote:
> The recent introduction of a bus master container added
> memory_region_add_subregion() into the PCI device registering path but
> missed memory_region_del_subregion() in the unregistering path leaving
> a reference to the root memory region of the new container.
> 
> This adds missing memory_region_del_subregion().
> 
> Fixes: 3716d5902d743 ("pci: introduce a bus master container")
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  hw/pci/pci.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index e6b08e1988..bd8043c460 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -869,6 +869,8 @@ static void do_pci_unregister_device(PCIDevice *pci_dev)
>      pci_dev->bus->devices[pci_dev->devfn] = NULL;
>      pci_config_free(pci_dev);
>  
> +    memory_region_del_subregion(&pci_dev->bus_master_container_region,
> +                                &pci_dev->bus_master_enable_region);
>      address_space_destroy(&pci_dev->bus_master_as);
>  }
>  
> 

My own review fail.  The enable subregion would be deleted when a memory
region is finalized, but the enable subregions is keeping the owner
alive.  And until the owner is alive, the container region is not
deleted either.  So there is a reference count cycle, which we need to
break.

It's probably good to revisit commit 2e2b8eb ("memory: allow destroying
a non-empty MemoryRegion", 2015-10-01).  For 2.9,

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

Re: [Qemu-devel] [PATCH qemu] pci: Add missing drop of bus master AS reference

Posted by David Gibson 7 years ago

On Mon, Mar 27, 2017 at 05:28:17PM +0200, Paolo Bonzini wrote:
> 
> 
> On 27/03/2017 06:40, Alexey Kardashevskiy wrote:
> > The recent introduction of a bus master container added
> > memory_region_add_subregion() into the PCI device registering path but
> > missed memory_region_del_subregion() in the unregistering path leaving
> > a reference to the root memory region of the new container.
> > 
> > This adds missing memory_region_del_subregion().
> > 
> > Fixes: 3716d5902d743 ("pci: introduce a bus master container")
> > Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> > ---
> >  hw/pci/pci.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > index e6b08e1988..bd8043c460 100644
> > --- a/hw/pci/pci.c
> > +++ b/hw/pci/pci.c
> > @@ -869,6 +869,8 @@ static void do_pci_unregister_device(PCIDevice *pci_dev)
> >      pci_dev->bus->devices[pci_dev->devfn] = NULL;
> >      pci_config_free(pci_dev);
> >  
> > +    memory_region_del_subregion(&pci_dev->bus_master_container_region,
> > +                                &pci_dev->bus_master_enable_region);
> >      address_space_destroy(&pci_dev->bus_master_as);
> >  }
> >  
> > 
> 
> My own review fail.  The enable subregion would be deleted when a memory
> region is finalized, but the enable subregions is keeping the owner
> alive.  And until the owner is alive, the container region is not
> deleted either.  So there is a reference count cycle, which we need to
> break.
> 
> It's probably good to revisit commit 2e2b8eb ("memory: allow destroying
> a non-empty MemoryRegion", 2015-10-01).  For 2.9,
> 
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Merged to ppc-for-2.9.

-- 
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

Re: [Qemu-devel] [PATCH qemu] pci: Add missing drop of bus master AS reference

Posted by Michael S. Tsirkin 7 years ago

On Tue, Mar 28, 2017 at 11:06:28AM +1100, David Gibson wrote:
> On Mon, Mar 27, 2017 at 05:28:17PM +0200, Paolo Bonzini wrote:
> > 
> > 
> > On 27/03/2017 06:40, Alexey Kardashevskiy wrote:
> > > The recent introduction of a bus master container added
> > > memory_region_add_subregion() into the PCI device registering path but
> > > missed memory_region_del_subregion() in the unregistering path leaving
> > > a reference to the root memory region of the new container.
> > > 
> > > This adds missing memory_region_del_subregion().
> > > 
> > > Fixes: 3716d5902d743 ("pci: introduce a bus master container")
> > > Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> > > ---
> > >  hw/pci/pci.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > > index e6b08e1988..bd8043c460 100644
> > > --- a/hw/pci/pci.c
> > > +++ b/hw/pci/pci.c
> > > @@ -869,6 +869,8 @@ static void do_pci_unregister_device(PCIDevice *pci_dev)
> > >      pci_dev->bus->devices[pci_dev->devfn] = NULL;
> > >      pci_config_free(pci_dev);
> > >  
> > > +    memory_region_del_subregion(&pci_dev->bus_master_container_region,
> > > +                                &pci_dev->bus_master_enable_region);
> > >      address_space_destroy(&pci_dev->bus_master_as);
> > >  }
> > >  
> > > 
> > 
> > My own review fail.  The enable subregion would be deleted when a memory
> > region is finalized, but the enable subregions is keeping the owner
> > alive.  And until the owner is alive, the container region is not
> > deleted either.  So there is a reference count cycle, which we need to
> > break.
> > 
> > It's probably good to revisit commit 2e2b8eb ("memory: allow destroying
> > a non-empty MemoryRegion", 2015-10-01).  For 2.9,
> > 
> > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> Merged to ppc-for-2.9.

I have it on pci branch, seems more appropriate.

> -- 
> 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

Re: [Qemu-devel] [PATCH qemu] pci: Add missing drop of bus master AS reference

Posted by David Gibson 7 years ago

On Tue, Mar 28, 2017 at 05:33:48AM +0300, Michael S. Tsirkin wrote:
> On Tue, Mar 28, 2017 at 11:06:28AM +1100, David Gibson wrote:
> > On Mon, Mar 27, 2017 at 05:28:17PM +0200, Paolo Bonzini wrote:
> > > 
> > > 
> > > On 27/03/2017 06:40, Alexey Kardashevskiy wrote:
> > > > The recent introduction of a bus master container added
> > > > memory_region_add_subregion() into the PCI device registering path but
> > > > missed memory_region_del_subregion() in the unregistering path leaving
> > > > a reference to the root memory region of the new container.
> > > > 
> > > > This adds missing memory_region_del_subregion().
> > > > 
> > > > Fixes: 3716d5902d743 ("pci: introduce a bus master container")
> > > > Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> > > > ---
> > > >  hw/pci/pci.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > > 
> > > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > > > index e6b08e1988..bd8043c460 100644
> > > > --- a/hw/pci/pci.c
> > > > +++ b/hw/pci/pci.c
> > > > @@ -869,6 +869,8 @@ static void do_pci_unregister_device(PCIDevice *pci_dev)
> > > >      pci_dev->bus->devices[pci_dev->devfn] = NULL;
> > > >      pci_config_free(pci_dev);
> > > >  
> > > > +    memory_region_del_subregion(&pci_dev->bus_master_container_region,
> > > > +                                &pci_dev->bus_master_enable_region);
> > > >      address_space_destroy(&pci_dev->bus_master_as);
> > > >  }
> > > >  
> > > > 
> > > 
> > > My own review fail.  The enable subregion would be deleted when a memory
> > > region is finalized, but the enable subregions is keeping the owner
> > > alive.  And until the owner is alive, the container region is not
> > > deleted either.  So there is a reference count cycle, which we need to
> > > break.
> > > 
> > > It's probably good to revisit commit 2e2b8eb ("memory: allow destroying
> > > a non-empty MemoryRegion", 2015-10-01).  For 2.9,
> > > 
> > > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> > 
> > Merged to ppc-for-2.9.
> 
> I have it on pci branch, seems more appropriate.

Good point.  I've dropped it from my tree.

-- 
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

Re: [Qemu-devel] [PATCH qemu] pci: Add missing drop of bus master AS reference

Posted by Jason Wang 7 years ago


On 2017年03月27日 12:40, Alexey Kardashevskiy wrote:
> The recent introduction of a bus master container added
> memory_region_add_subregion() into the PCI device registering path but
> missed memory_region_del_subregion() in the unregistering path leaving
> a reference to the root memory region of the new container.
>
> This adds missing memory_region_del_subregion().
>
> Fixes: 3716d5902d743 ("pci: introduce a bus master container")
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>   hw/pci/pci.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index e6b08e1988..bd8043c460 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -869,6 +869,8 @@ static void do_pci_unregister_device(PCIDevice *pci_dev)
>       pci_dev->bus->devices[pci_dev->devfn] = NULL;
>       pci_config_free(pci_dev);
>   
> +    memory_region_del_subregion(&pci_dev->bus_master_container_region,
> +                                &pci_dev->bus_master_enable_region);
>       address_space_destroy(&pci_dev->bus_master_as);
>   }
>   

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks!