[PATCH v4] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb)
Mauricio Faria de Oliveira
mauricfo at linux.vnet.ibm.com
Fri Aug 12 06:25:40 AEST 2016
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 at linux.vnet.ibm.com>
Signed-off-by: Mauricio Faria de Oliveira <mauricfo at 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
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