PCI: add a member in 'struct pci_bus' to record the original 'pci_ops'

hulk inclusion
category: bugfix
bugzilla: NA
CVE: NA

-------------------------------------------------

When I test 'aer-inject' with the following procedures:
1. inject a fatal error into a upstream PCI bridge
2. remove the upstream bridge by sysfs
3. rescan the PCI tree by 'echo 1 > /sys/bus/pci/rescan'
4. execute command 'rmmod aer-inject'
5. remove the upstream bridge by sysfs again

I came across the following Oops.

[  799.713238] Internal error: Oops: 96000007 [#1] SMP
[  799.718099] Process bash (pid: 10683, stack limit = 0x00000000125a3b1b)
[  799.724686] CPU: 108 PID: 10683 Comm: bash Kdump: loaded Not tainted 4.19.36 #2
[  799.731962] Hardware name: Huawei TaiShan 2280 V2/BC82AMDD, BIOS 1.05 09/18/2019
[  799.739325] pstate: 40400009 (nZcv daif +PAN -UAO)
[  799.744104] pc : pci_remove_bus+0xc0/0x1c0
[  799.748182] lr : pci_remove_bus+0x94/0x1c0
[  799.752260] sp : ffffa02e335df940
[  799.755560] x29: ffffa02e335df940 x28: ffff2000088216a8
[  799.760849] x27: 1ffff405c66bbfbc x26: ffff20000a9518c0
[  799.766139] x25: ffffa02dea6ec418 x24: 1ffff405bd4dd883
[  799.771427] x23: ffffa02e72576628 x22: 1ffff405ce4aecc0
[  799.776715] x21: ffffa02e72576608 x20: ffff200002e75080
[  799.782003] x19: ffffa02e72576600 x18: 0000000000000000
[  799.787291] x17: 0000000000000000 x16: 0000000000000000
[  799.792578] x15: 0000000000000001 x14: dfff200000000000
[  799.797866] x13: ffff20000a6dfaf0 x12: 0000000000000000
[  799.803154] x11: 1fffe4000159b217 x10: ffff04000159b217
[  799.808442] x9 : dfff200000000000 x8 : ffff20000acd90bf
[  799.813730] x7 : 0000000000000000 x6 : 0000000000000000
[  799.819017] x5 : 0000000000000001 x4 : 0000000000000000
[  799.824306] x3 : 1ffff405dbe62603 x2 : 1fffe400005cea11
[  799.829593] x1 : dfff200000000000 x0 : ffff200002e75088
[  799.834882] Call trace:
[  799.837323]  pci_remove_bus+0xc0/0x1c0
[  799.841056]  pci_remove_bus_device+0xd0/0x2f0
[  799.845392]  pci_stop_and_remove_bus_device_locked+0x2c/0x40
[  799.851028]  remove_store+0x1b8/0x1d0
[  799.854679]  dev_attr_store+0x60/0x80
[  799.858330]  sysfs_kf_write+0x104/0x170
[  799.862149]  kernfs_fop_write+0x23c/0x430
[  799.866143]  __vfs_write+0xec/0x4e0
[  799.869615]  vfs_write+0x12c/0x3d0
[  799.873001]  ksys_write+0xd0/0x190
[  799.876389]  __arm64_sys_write+0x70/0xa0
[  799.880298]  el0_svc_common+0xfc/0x278
[  799.884030]  el0_svc_handler+0x50/0xc0
[  799.887764]  el0_svc+0x8/0xc
[  799.890634] Code: d2c40001 f2fbffe1 91002280 d343fc02 (38e16841)
[  799.896700] kernel fault(0x1) notification starting on CPU 108

It is because when we alloc a new bus in rescanning process, the
'pci_ops' of the newly allocced 'pci_bus' is inherited from its parent
pci bus. Whereas, the 'pci_ops' of the parent bus may be changed to
'aer_inj_pci_ops' in 'aer_inject()'. When we unload the module
'aer_inject', we only restore the 'pci_ops' for the pci bus of the
error-injected device and the root port in 'aer_inject_exit'. After we
have unloaded the module, the 'pci_ops' of the newly allocced pci bus is
still 'aer_inj_pci_ops'. When we access it, an Oops happened.

This patch add a member 'backup_ops' in 'struct pci_bus' to record the
original 'ops'. When we alloc a child pci bus, we assign the
'backup_ops' of the parent bus to the 'ops' of the child bus.

Maybe the best way is to not modify the 'pci_ops' in 'struct pci_bus',
but this will refactor the 'aer_inject' framework a lot. I haven't found
a better way to handle it.
Signed-off-by: NXiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/pci/probe.c

@@ -848,6 +848,7 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	bus->sysdata = bridge->sysdata;
 	bus->msi = bridge->msi;
 	bus->ops = bridge->ops;
+	bus->backup_ops = bus->ops;
 	bus->number = bus->busn_res.start = bridge->busnr;
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
 	bus->domain_nr = pci_bus_find_domain_nr(bus, parent);
@@ -993,7 +994,11 @@ static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
 		return NULL;
 
 	child->parent = parent;
-	child->ops = parent->ops;
+	if (parent->backup_ops)
+		child->ops = parent->backup_ops;
+	else
+		child->ops = parent->ops;
+	child->backup_ops = child->ops;
 	child->msi = parent->msi;
 	child->sysdata = parent->sysdata;
 	child->bus_flags = parent->bus_flags;

include/linux/pci.h

@@ -584,6 +584,7 @@ struct pci_bus {
 	struct resource busn_res;	/* Bus numbers routed to this bus */
 
 	struct pci_ops	*ops;		/* Configuration access functions */
+	struct pci_ops	*backup_ops;
 	struct msi_controller *msi;	/* MSI controller */
 	void		*sysdata;	/* Hook for sys-specific extension */
 	struct proc_dir_entry *procdir;	/* Directory entry in /proc/bus/pci */