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Violators will be prosecuted for from ; Thu, 11 Aug 2016 16:41:09 +1000 Received: from d23relay06.au.ibm.com (d23relay06.au.ibm.com [9.185.63.219]) by d23dlp03.au.ibm.com (Postfix) with ESMTP id 3F8DB3578056 for ; Thu, 11 Aug 2016 16:41:08 +1000 (EST) Received: from d23av06.au.ibm.com (d23av06.au.ibm.com [9.190.235.151]) by d23relay06.au.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u7B6f8eF32047204 for ; Thu, 11 Aug 2016 16:41:08 +1000 Received: from d23av06.au.ibm.com (localhost [127.0.0.1]) by d23av06.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u7B6f7iZ010493 for ; Thu, 11 Aug 2016 16:41:08 +1000 Date: Thu, 11 Aug 2016 16:40:36 +1000 From: Gavin Shan To: Mauricio Faria de Oliveira Cc: linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au, gwshan@linux.vnet.ibm.com, andrew.donnellan@au1.ibm.com Subject: Re: [PATCH v3] powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb) Reply-To: Gavin Shan References: <1470865522-28046-1-git-send-email-mauricfo@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1470865522-28046-1-git-send-email-mauricfo@linux.vnet.ibm.com> Message-Id: <20160811064036.GB3787@gwshan> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Aug 10, 2016 at 06:45:22PM -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_host_bridge_release()' function to be set >as .release_fn(), which expects .release_data to hold the pointer to >the pci_controller to kfree(). > >It enables that functionality for pseries (although it isn't platform >-specific, and may be used by cxl). It keeps pcibios_free_controller() >backwards-compatible (i.e., kfree(phb) in it) in case no .release_fn() >is defined for the pci_controller. > >Details on not-so-elegant design choices: > > - Added 'pci_controller.bridge' field (pointer to associated 'struct > pci_host_bridge') so *not* to use 'pci_find_host_bridge(phb->bus)' > in pcibios_free_controller(). > > That's because remove_phb_dynamic() sets 'phb->bus = NULL' before > pcibios_free_controller(). That seems to be very important, with > commit title 'powerpc/pci: Fix various pseries PCI hotplug issues' > (so I'll not remove it just to avoid this null pointer dereference). > > - Used 'pci_host_bridge.release_data' field (pointer to associated > 'struct pci_controller') so *not* to 'pci_bus_to_host(bridge->bus)' > in pcibios_host_bridge_release(). > > 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_host_bridge_release(), 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: > > # 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. > [ 479.547020] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01 > [ 479.547049] pci_hp_remove_devices: Removing 0021:01:00.0... > ... > [ 483.536303] pci_hp_remove_devices: Removing 0021:01:00.1... > ... > [ 497.072130] pci_bus 0021:01: busn_res: [bus 01-ff] is released > [ 497.072209] rpadlpar_io: slot PHB 33 removed > > # kill -9 $pid1 > # kill -9 $pid2 > [ 506.604458] pcibios_host_bridge_release: domain 33, dynamic 1 > >Suggested-By: Gavin Shan >Signed-off-by: Mauricio Faria de Oliveira > >Changelog: > - v3: different approach: struct pci_host_bridge.release_fn() > - v2: different approach: struct pci_controller.refcount >--- > arch/powerpc/include/asm/pci-bridge.h | 2 ++ > arch/powerpc/kernel/pci-common.c | 15 ++++++++++++++- > arch/powerpc/platforms/pseries/pci.c | 3 +++ > 3 files changed, 19 insertions(+), 1 deletion(-) > >diff --git a/arch/powerpc/include/asm/pci-bridge.h b/arch/powerpc/include/asm/pci-bridge.h >index b5e88e4..9b11631 100644 >--- a/arch/powerpc/include/asm/pci-bridge.h >+++ b/arch/powerpc/include/asm/pci-bridge.h >@@ -54,6 +54,7 @@ struct pci_controller_ops { > */ > struct pci_controller { > struct pci_bus *bus; >+ struct pci_host_bridge *bridge; /* associated 'PHB' in PCI subsystem */ > char is_dynamic; > #ifdef CONFIG_PPC64 > int node; >@@ -301,6 +302,7 @@ 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_host_bridge_release(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..c5b5f60 100644 >--- a/arch/powerpc/kernel/pci-common.c >+++ b/arch/powerpc/kernel/pci-common.c >@@ -145,11 +145,23 @@ void pcibios_free_controller(struct pci_controller *phb) > list_del(&phb->list_node); > spin_unlock(&hose_spinlock); > >- if (phb->is_dynamic) >+ /* if the associated pci_host_bridge has a release_fn(), rely on that. */ >+ if (!phb->bridge->release_fn && phb->is_dynamic) > kfree(phb); > } > EXPORT_SYMBOL_GPL(pcibios_free_controller); > >+void pcibios_host_bridge_release(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); >+ >+ if (phb->is_dynamic) >+ kfree(phb); >+} >+EXPORT_SYMBOL_GPL(pcibios_host_bridge_release); >+ It seems the user has two options here: (1) Setup bridge's release_fn() and call pcibios_free_controller() explicitly; (2) Call pcibios_free_controller() without a valid bridge's release_fn() initialized. I think we can provide better interface to users: what we do in pcibios_free_controller() and pcibios_host_bridge_release() should be (almost) same. pcibios_host_bridge_release() can be a wrapper of pcibios_free_controller(). With this, the users have two options: (1) Rely on bridge's release_fn() to free the PCI controller; (2) Call pcibios_free_controller() as we're doing currently. Those two options corresponds to immediately or deferred releasing. > /* > * The function is used to return the minimal alignment > * for memory or I/O windows of the associated P2P bridge. >@@ -1646,6 +1658,7 @@ void pcibios_scan_phb(struct pci_controller *hose) > return; > } > hose->bus = bus; >+ hose->bridge = pci_find_host_bridge(bus); > > /* Get probe mode and perform scan */ > mode = PCI_PROBE_NORMAL; >diff --git a/arch/powerpc/platforms/pseries/pci.c b/arch/powerpc/platforms/pseries/pci.c >index fe16a50..146d5da 100644 >--- a/arch/powerpc/platforms/pseries/pci.c >+++ b/arch/powerpc/platforms/pseries/pci.c >@@ -119,6 +119,9 @@ int pseries_root_bridge_prepare(struct pci_host_bridge *bridge) > > bus = bridge->bus; > >+ pci_set_host_bridge_release(bridge, pcibios_host_bridge_release, >+ (void *) pci_bus_to_host(bus)); >+ > dn = pcibios_get_phb_of_node(bus); > if (!dn) > return 0; Thanks, Gavin >-- >1.8.3.1 >