[PATCH v4] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb)

[PATCH v4] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb)

[Mauricio Faria de Oliveira]

This patch leverages 'struct pci_host_bridge' from the PCI subsystem
in order to free the pci_controller only after the last reference to
its devices is dropped (avoiding an oops in pcibios_release_device()
if the last reference is dropped after pcibios_free_controller()).

The patch relies on pci_host_bridge.release_fn() (and .release_data),
which is called automatically by the PCI subsystem when the root bus
is released (i.e., the last reference is dropped).  Those fields are
set via pci_set_host_bridge_release() (e.g. in the platform-specific
implementation of pcibios_root_bridge_prepare()).

It introduces the 'pcibios_free_controller_deferred()' .release_fn()
and it expects .release_data to hold a pointer to the pci_controller.

The function implictly calls 'pcibios_free_controller()', so an user
must *NOT* explicitly call it if using the new _deferred() callback.

The functionality is enabled for pseries (although it isn't platform
specific, and may be used by cxl).

Details on not-so-elegant design choices:

 - Use 'pci_host_bridge.release_data' field as pointer to associated
   'struct pci_controller' so *not* to 'pci_bus_to_host(bridge->bus)'
   in pcibios_free_controller_deferred().

   That's because pci_remove_root_bus() sets 'host_bridge->bus = NULL'
   (so, if the last reference is released after pci_remove_root_bus()
   runs, which eventually reaches pcibios_free_controller_deferred(),
   that would hit a null pointer dereference).

   The cxl/vphb.c code calls pci_remove_root_bus(), and the cxl folks
   are interested in this fix.

Test-case #1 (hold references)

  # ls -ld /sys/block/sd* | grep -m1 0021:01:00.0
  <...> /sys/block/sdaa -> ../devices/pci0021:01/0021:01:00.0/<...>

  # ls -ld /sys/block/sd* | grep -m1 0021:01:00.1
  <...> /sys/block/sdab -> ../devices/pci0021:01/0021:01:00.1/<...>

  # cat >/dev/sdaa & pid1=$!
  # cat >/dev/sdab & pid2=$!

  # drmgr -w 5 -d 1 -c phb -s 'PHB 33' -r
  Validating PHB DLPAR capability...yes.
  [  594.306719] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01
  [  594.306738] pci_hp_remove_devices:    Removing 0021:01:00.0...
  ...
  [  598.236381] pci_hp_remove_devices:    Removing 0021:01:00.1...
  ...
  [  611.972077] pci_bus 0021:01: busn_res: [bus 01-ff] is released
  [  611.972140] rpadlpar_io: slot PHB 33 removed

  # kill -9 $pid1
  # kill -9 $pid2
  [  632.918088] pcibios_free_controller_deferred: domain 33, dynamic 1

Test-case #2 (don't hold references)

  # drmgr -w 5 -d 1 -c phb -s 'PHB 33' -r
  Validating PHB DLPAR capability...yes.
  [  916.357363] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01
  [  916.357386] pci_hp_remove_devices:    Removing 0021:01:00.0...
  ...
  [  920.566527] pci_hp_remove_devices:    Removing 0021:01:00.1...
  ...
  [  933.955873] pci_bus 0021:01: busn_res: [bus 01-ff] is released
  [  933.955977] pcibios_free_controller_deferred: domain 33, dynamic 1
  [  933.955999] rpadlpar_io: slot PHB 33 removed

Suggested-By: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
---
Changelog:
 - v4: improve usability/design/documentation:
       - rename function to pcibios_free_controller_deferred()
       - from function call pcibios_free_controller()
       - no more struct pci_controller.bridge field
       thanks: Gavin Shan, Andrew Donnellan
 - v3: different approach: struct pci_host_bridge.release_fn()
 - v2: different approach: struct pci_controller.refcount 

 arch/powerpc/include/asm/pci-bridge.h      |  1 +
 arch/powerpc/kernel/pci-common.c           | 36 ++++++++++++++++++++++++++++++
 arch/powerpc/platforms/pseries/pci.c       |  4 ++++
 arch/powerpc/platforms/pseries/pci_dlpar.c |  7 ++++--
 4 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/pci-bridge.h b/arch/powerpc/include/asm/pci-bridge.h
index b5e88e4..c0309c5 100644
--- a/arch/powerpc/include/asm/pci-bridge.h
+++ b/arch/powerpc/include/asm/pci-bridge.h
@@ -301,6 +301,7 @@ extern void pci_process_bridge_OF_ranges(struct pci_controller *hose,
 /* Allocate & free a PCI host bridge structure */
 extern struct pci_controller *pcibios_alloc_controller(struct device_node *dev);
 extern void pcibios_free_controller(struct pci_controller *phb);
+extern void pcibios_free_controller_deferred(struct pci_host_bridge *bridge);
 
 #ifdef CONFIG_PCI
 extern int pcibios_vaddr_is_ioport(void __iomem *address);
diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index a5c0153..8c48a78 100644
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c
@@ -151,6 +151,42 @@ void pcibios_free_controller(struct pci_controller *phb)
 EXPORT_SYMBOL_GPL(pcibios_free_controller);
 
 /*
+ * This function is used to call pcibios_free_controller()
+ * in a deferred manner: a callback from the PCI subsystem.
+ *
+ * _*DO NOT*_ call pcibios_free_controller() explicitly if
+ * this is used (or it may access an invalid *phb pointer).
+ *
+ * The callback occurs when all references to the root bus
+ * are dropped (e.g., child buses/devices and their users).
+ *
+ * It's called as .release_fn() of 'struct pci_host_bridge'
+ * which is associated with the 'struct pci_controller.bus'
+ * (root bus) - it expects .release_data to hold a pointer
+ * to 'struct pci_controller'.
+ *
+ * In order to use it, register .release_fn()/release_data
+ * like this:
+ *
+ * pci_set_host_bridge_release(bridge,
+ *                             pcibios_free_controller_deferred
+ *                             (void *) phb);
+ *
+ * e.g. in the pcibios_root_bridge_prepare() callback from
+ * pci_create_root_bus().
+ */
+void pcibios_free_controller_deferred(struct pci_host_bridge *bridge)
+{
+	struct pci_controller *phb = (struct pci_controller *)
+					 bridge->release_data;
+
+	pr_debug("domain %d, dynamic %d\n", phb->global_number, phb->is_dynamic);
+
+	pcibios_free_controller(phb);
+}
+EXPORT_SYMBOL_GPL(pcibios_free_controller_deferred);
+
+/*
  * The function is used to return the minimal alignment
  * for memory or I/O windows of the associated P2P bridge.
  * By default, 4KiB alignment for I/O windows and 1MiB for
diff --git a/arch/powerpc/platforms/pseries/pci.c b/arch/powerpc/platforms/pseries/pci.c
index fe16a50..09eba5a 100644
--- a/arch/powerpc/platforms/pseries/pci.c
+++ b/arch/powerpc/platforms/pseries/pci.c
@@ -119,6 +119,10 @@ int pseries_root_bridge_prepare(struct pci_host_bridge *bridge)
 
 	bus = bridge->bus;
 
+	/* Rely on the pcibios_free_controller_deferred() callback. */
+	pci_set_host_bridge_release(bridge, pcibios_free_controller_deferred,
+					(void *) pci_bus_to_host(bus));
+
 	dn = pcibios_get_phb_of_node(bus);
 	if (!dn)
 		return 0;
diff --git a/arch/powerpc/platforms/pseries/pci_dlpar.c b/arch/powerpc/platforms/pseries/pci_dlpar.c
index 906dbaa..547fd13 100644
--- a/arch/powerpc/platforms/pseries/pci_dlpar.c
+++ b/arch/powerpc/platforms/pseries/pci_dlpar.c
@@ -106,8 +106,11 @@ int remove_phb_dynamic(struct pci_controller *phb)
 		release_resource(res);
 	}
 
-	/* Free pci_controller data structure */
-	pcibios_free_controller(phb);
+	/*
+	 * The pci_controller data structure is freed by
+	 * the pcibios_free_controller_deferred() callback;
+	 * see pseries_root_bridge_prepare().
+	 */
 
 	return 0;
 }
-- 
1.8.3.1

Re: [PATCH v4] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb)

[Gavin Shan]

On Thu, Aug 11, 2016 at 05:25:40PM -0300, Mauricio Faria de Oliveira wrote:
>This patch leverages 'struct pci_host_bridge' from the PCI subsystem
>in order to free the pci_controller only after the last reference to
>its devices is dropped (avoiding an oops in pcibios_release_device()
>if the last reference is dropped after pcibios_free_controller()).
>
>The patch relies on pci_host_bridge.release_fn() (and .release_data),
>which is called automatically by the PCI subsystem when the root bus
>is released (i.e., the last reference is dropped).  Those fields are
>set via pci_set_host_bridge_release() (e.g. in the platform-specific
>implementation of pcibios_root_bridge_prepare()).
>
>It introduces the 'pcibios_free_controller_deferred()' .release_fn()
>and it expects .release_data to hold a pointer to the pci_controller.
>
>The function implictly calls 'pcibios_free_controller()', so an user
>must *NOT* explicitly call it if using the new _deferred() callback.
>
>The functionality is enabled for pseries (although it isn't platform
>specific, and may be used by cxl).
>
>Details on not-so-elegant design choices:
>
> - Use 'pci_host_bridge.release_data' field as pointer to associated
>   'struct pci_controller' so *not* to 'pci_bus_to_host(bridge->bus)'
>   in pcibios_free_controller_deferred().
>
>   That's because pci_remove_root_bus() sets 'host_bridge->bus = NULL'
>   (so, if the last reference is released after pci_remove_root_bus()
>   runs, which eventually reaches pcibios_free_controller_deferred(),
>   that would hit a null pointer dereference).
>
>   The cxl/vphb.c code calls pci_remove_root_bus(), and the cxl folks
>   are interested in this fix.
>
>Test-case #1 (hold references)
>
>  # ls -ld /sys/block/sd* | grep -m1 0021:01:00.0
>  <...> /sys/block/sdaa -> ../devices/pci0021:01/0021:01:00.0/<...>
>
>  # ls -ld /sys/block/sd* | grep -m1 0021:01:00.1
>  <...> /sys/block/sdab -> ../devices/pci0021:01/0021:01:00.1/<...>
>
>  # cat >/dev/sdaa & pid1=$!
>  # cat >/dev/sdab & pid2=$!
>
>  # drmgr -w 5 -d 1 -c phb -s 'PHB 33' -r
>  Validating PHB DLPAR capability...yes.
>  [  594.306719] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01
>  [  594.306738] pci_hp_remove_devices:    Removing 0021:01:00.0...
>  ...
>  [  598.236381] pci_hp_remove_devices:    Removing 0021:01:00.1...
>  ...
>  [  611.972077] pci_bus 0021:01: busn_res: [bus 01-ff] is released
>  [  611.972140] rpadlpar_io: slot PHB 33 removed
>
>  # kill -9 $pid1
>  # kill -9 $pid2
>  [  632.918088] pcibios_free_controller_deferred: domain 33, dynamic 1
>
>Test-case #2 (don't hold references)
>
>  # drmgr -w 5 -d 1 -c phb -s 'PHB 33' -r
>  Validating PHB DLPAR capability...yes.
>  [  916.357363] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01
>  [  916.357386] pci_hp_remove_devices:    Removing 0021:01:00.0...
>  ...
>  [  920.566527] pci_hp_remove_devices:    Removing 0021:01:00.1...
>  ...
>  [  933.955873] pci_bus 0021:01: busn_res: [bus 01-ff] is released
>  [  933.955977] pcibios_free_controller_deferred: domain 33, dynamic 1
>  [  933.955999] rpadlpar_io: slot PHB 33 removed
>
>Suggested-By: Gavin Shan <gwshan@linux.vnet.ibm.com>
>Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>

I don't have more obvious comments except below one nitpicky:

Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>

>---
>Changelog:
> - v4: improve usability/design/documentation:
>       - rename function to pcibios_free_controller_deferred()
>       - from function call pcibios_free_controller()
>       - no more struct pci_controller.bridge field
>       thanks: Gavin Shan, Andrew Donnellan
> - v3: different approach: struct pci_host_bridge.release_fn()
> - v2: different approach: struct pci_controller.refcount 
>
> arch/powerpc/include/asm/pci-bridge.h      |  1 +
> arch/powerpc/kernel/pci-common.c           | 36 ++++++++++++++++++++++++++++++
> arch/powerpc/platforms/pseries/pci.c       |  4 ++++
> arch/powerpc/platforms/pseries/pci_dlpar.c |  7 ++++--
> 4 files changed, 46 insertions(+), 2 deletions(-)
>
>diff --git a/arch/powerpc/include/asm/pci-bridge.h b/arch/powerpc/include/asm/pci-bridge.h
>index b5e88e4..c0309c5 100644
>--- a/arch/powerpc/include/asm/pci-bridge.h
>+++ b/arch/powerpc/include/asm/pci-bridge.h
>@@ -301,6 +301,7 @@ extern void pci_process_bridge_OF_ranges(struct pci_controller *hose,
> /* Allocate & free a PCI host bridge structure */
> extern struct pci_controller *pcibios_alloc_controller(struct device_node *dev);
> extern void pcibios_free_controller(struct pci_controller *phb);
>+extern void pcibios_free_controller_deferred(struct pci_host_bridge *bridge);
>
> #ifdef CONFIG_PCI
> extern int pcibios_vaddr_is_ioport(void __iomem *address);
>diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
>index a5c0153..8c48a78 100644
>--- a/arch/powerpc/kernel/pci-common.c
>+++ b/arch/powerpc/kernel/pci-common.c
>@@ -151,6 +151,42 @@ void pcibios_free_controller(struct pci_controller *phb)
> EXPORT_SYMBOL_GPL(pcibios_free_controller);
>
> /*
>+ * This function is used to call pcibios_free_controller()
>+ * in a deferred manner: a callback from the PCI subsystem.
>+ *
>+ * _*DO NOT*_ call pcibios_free_controller() explicitly if
>+ * this is used (or it may access an invalid *phb pointer).
>+ *
>+ * The callback occurs when all references to the root bus
>+ * are dropped (e.g., child buses/devices and their users).
>+ *
>+ * It's called as .release_fn() of 'struct pci_host_bridge'
>+ * which is associated with the 'struct pci_controller.bus'
>+ * (root bus) - it expects .release_data to hold a pointer
>+ * to 'struct pci_controller'.
>+ *
>+ * In order to use it, register .release_fn()/release_data
>+ * like this:
>+ *
>+ * pci_set_host_bridge_release(bridge,
>+ *                             pcibios_free_controller_deferred
>+ *                             (void *) phb);
>+ *
>+ * e.g. in the pcibios_root_bridge_prepare() callback from
>+ * pci_create_root_bus().
>+ */
>+void pcibios_free_controller_deferred(struct pci_host_bridge *bridge)
>+{
>+	struct pci_controller *phb = (struct pci_controller *)
>+					 bridge->release_data;
>+
>+	pr_debug("domain %d, dynamic %d\n", phb->global_number, phb->is_dynamic);
>+
>+	pcibios_free_controller(phb);
>+}
>+EXPORT_SYMBOL_GPL(pcibios_free_controller_deferred);
>+

It might be nicer for users to implement their own pcibios_free_controller_deferred(),
meaning pSeries needs its own implementation for now. The reason is more user (pSeries)
specific objects can be released together with the PHB. However, I'm still fine without
the comment to be covered.

>+/*
>  * The function is used to return the minimal alignment
>  * for memory or I/O windows of the associated P2P bridge.
>  * By default, 4KiB alignment for I/O windows and 1MiB for
>diff --git a/arch/powerpc/platforms/pseries/pci.c b/arch/powerpc/platforms/pseries/pci.c
>index fe16a50..09eba5a 100644
>--- a/arch/powerpc/platforms/pseries/pci.c
>+++ b/arch/powerpc/platforms/pseries/pci.c
>@@ -119,6 +119,10 @@ int pseries_root_bridge_prepare(struct pci_host_bridge *bridge)
>
> 	bus = bridge->bus;
>
>+	/* Rely on the pcibios_free_controller_deferred() callback. */
>+	pci_set_host_bridge_release(bridge, pcibios_free_controller_deferred,
>+					(void *) pci_bus_to_host(bus));
>+
> 	dn = pcibios_get_phb_of_node(bus);
> 	if (!dn)
> 		return 0;
>diff --git a/arch/powerpc/platforms/pseries/pci_dlpar.c b/arch/powerpc/platforms/pseries/pci_dlpar.c
>index 906dbaa..547fd13 100644
>--- a/arch/powerpc/platforms/pseries/pci_dlpar.c
>+++ b/arch/powerpc/platforms/pseries/pci_dlpar.c
>@@ -106,8 +106,11 @@ int remove_phb_dynamic(struct pci_controller *phb)
> 		release_resource(res);
> 	}
>
>-	/* Free pci_controller data structure */
>-	pcibios_free_controller(phb);
>+	/*
>+	 * The pci_controller data structure is freed by
>+	 * the pcibios_free_controller_deferred() callback;
>+	 * see pseries_root_bridge_prepare().
>+	 */
>
> 	return 0;
> }

Thanks,
Gavin

Re: [PATCH v4] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb)

[Andrew Donnellan]

On 12/08/16 15:54, Gavin Shan wrote:
> It might be nicer for users to implement their own pcibios_free_controller_deferred(),
> meaning pSeries needs its own implementation for now. The reason is more user (pSeries)
> specific objects can be released together with the PHB. However, I'm still fine without
> the comment to be covered.

That's probably not a bad idea, though from a cxl perspective I'm fine 
with using the current version.

-- 
Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan@au1.ibm.com  IBM Australia Limited

Re: [PATCH v4] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb)

[Andrew Donnellan]

On 12/08/16 06:25, Mauricio Faria de Oliveira wrote:
> This patch leverages 'struct pci_host_bridge' from the PCI subsystem
> in order to free the pci_controller only after the last reference to
> its devices is dropped (avoiding an oops in pcibios_release_device()
> if the last reference is dropped after pcibios_free_controller()).
>
> The patch relies on pci_host_bridge.release_fn() (and .release_data),
> which is called automatically by the PCI subsystem when the root bus
> is released (i.e., the last reference is dropped).  Those fields are
> set via pci_set_host_bridge_release() (e.g. in the platform-specific
> implementation of pcibios_root_bridge_prepare()).
>
> It introduces the 'pcibios_free_controller_deferred()' .release_fn()
> and it expects .release_data to hold a pointer to the pci_controller.
>
> The function implictly calls 'pcibios_free_controller()', so an user
> must *NOT* explicitly call it if using the new _deferred() callback.
>
> The functionality is enabled for pseries (although it isn't platform
> specific, and may be used by cxl).
>
> Details on not-so-elegant design choices:
>
>  - Use 'pci_host_bridge.release_data' field as pointer to associated
>    'struct pci_controller' so *not* to 'pci_bus_to_host(bridge->bus)'
>    in pcibios_free_controller_deferred().
>
>    That's because pci_remove_root_bus() sets 'host_bridge->bus = NULL'
>    (so, if the last reference is released after pci_remove_root_bus()
>    runs, which eventually reaches pcibios_free_controller_deferred(),
>    that would hit a null pointer dereference).
>
>    The cxl/vphb.c code calls pci_remove_root_bus(), and the cxl folks
>    are interested in this fix.
>
> Test-case #1 (hold references)
>
>   # ls -ld /sys/block/sd* | grep -m1 0021:01:00.0
>   <...> /sys/block/sdaa -> ../devices/pci0021:01/0021:01:00.0/<...>
>
>   # ls -ld /sys/block/sd* | grep -m1 0021:01:00.1
>   <...> /sys/block/sdab -> ../devices/pci0021:01/0021:01:00.1/<...>
>
>   # cat >/dev/sdaa & pid1=$!
>   # cat >/dev/sdab & pid2=$!
>
>   # drmgr -w 5 -d 1 -c phb -s 'PHB 33' -r
>   Validating PHB DLPAR capability...yes.
>   [  594.306719] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01
>   [  594.306738] pci_hp_remove_devices:    Removing 0021:01:00.0...
>   ...
>   [  598.236381] pci_hp_remove_devices:    Removing 0021:01:00.1...
>   ...
>   [  611.972077] pci_bus 0021:01: busn_res: [bus 01-ff] is released
>   [  611.972140] rpadlpar_io: slot PHB 33 removed
>
>   # kill -9 $pid1
>   # kill -9 $pid2
>   [  632.918088] pcibios_free_controller_deferred: domain 33, dynamic 1
>
> Test-case #2 (don't hold references)
>
>   # drmgr -w 5 -d 1 -c phb -s 'PHB 33' -r
>   Validating PHB DLPAR capability...yes.
>   [  916.357363] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01
>   [  916.357386] pci_hp_remove_devices:    Removing 0021:01:00.0...
>   ...
>   [  920.566527] pci_hp_remove_devices:    Removing 0021:01:00.1...
>   ...
>   [  933.955873] pci_bus 0021:01: busn_res: [bus 01-ff] is released
>   [  933.955977] pcibios_free_controller_deferred: domain 33, dynamic 1
>   [  933.955999] rpadlpar_io: slot PHB 33 removed
>
> Suggested-By: Gavin Shan <gwshan@linux.vnet.ibm.com>
> Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>

Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Tested-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl

Does this justify a Cc: stable?

-- 
Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan@au1.ibm.com  IBM Australia Limited

Re: [PATCH v4] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb)

[Mauricio Faria de Oliveira]

On 08/12/2016 03:03 AM, Andrew Donnellan wrote:
> On 12/08/16 15:54, Gavin Shan wrote:
>> It might be nicer for users to implement their own
>> pcibios_free_controller_deferred(),
>> meaning pSeries needs its own implementation for now. The reason is
>> more user (pSeries)
>> specific objects can be released together with the PHB. However, I'm
>> still fine without
>> the comment to be covered.
>
> That's probably not a bad idea, though from a cxl perspective I'm fine
> with using the current version.

I agree, but in that case the user _still_ can use another function.
This patch just provides an implementation that defaults to what was
already done, in a deferred manner.

If some users need something more specific, they can wire it up too :)
the same way we did - and it's explained in the function's comments.

Thanks for the review, suggestions and reaching a better and much more
interesting patch.

-- 
Mauricio Faria de Oliveira
IBM Linux Technology Center

Re: [PATCH v4] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb)

[Mauricio Faria de Oliveira]

Michael,

On 08/12/2016 02:54 AM, Gavin Shan wrote:
 > I don't have more obvious comments except below one nitpicky:

I just addressed/replied this in the other e-mail; i think it's OK,
and Andrew/cxl is OK w/ it too.

 > Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>


On 08/12/2016 03:06 AM, Andrew Donnellan wrote:
>> Suggested-By: Gavin Shan <gwshan@linux.vnet.ibm.com>
>> Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
>
> Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
> Tested-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
>
> Does this justify a Cc: stable?

I'd think so, since this prevents an oops & crash (w/ panic_on_oops).
Do you agree?

Thanks!

-- 
Mauricio Faria de Oliveira
IBM Linux Technology Center