of: platform: stop accessing invalid dev in of_platform_device_destroy

Immediately after the platform_device_unregister() the device will be
cleaned up. Accessing the freed pointer immediately after that will
crash the system.

Found this bug when kernel is built with CONFIG_PAGE_POISONING and testing
loading/unloading audio drivers in a loop on Qcom platforms.

Fix this by moving of_node_clear_flag() just before the unregister calls.

Below is the crash trace:

Unable to handle kernel paging request at virtual address 6b6b6b6b6b6c03
Mem abort info:
  ESR = 0x96000021
  Exception class = DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
Data abort info:
  ISV = 0, ISS = 0x00000021
  CM = 0, WnR = 0
[006b6b6b6b6b6c03] address between user and kernel address ranges
Internal error: Oops: 96000021 [#1] PREEMPT SMP
Modules linked in:
CPU: 2 PID: 1784 Comm: sh Tainted: G        W         4.17.0-rc7-02230-ge3a63a7ef641-dirty #204
Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
pstate: 80000005 (Nzcv daif -PAN -UAO)
pc : clear_bit+0x18/0x2c
lr : of_platform_device_destroy+0x64/0xb8
sp : ffff00000c9c3930
x29: ffff00000c9c3930 x28: ffff80003d39b200
x27: ffff000008bb1000 x26: 0000000000000040
x25: 0000000000000124 x24: ffff80003a9a3080
x23: 0000000000000060 x22: ffff00000939f518
x21: ffff80003aa79e98 x20: ffff80003aa3dae0
x19: ffff80003aa3c890 x18: ffff800009feb794
x17: 0000000000000000 x16: 0000000000000000
x15: ffff800009feb790 x14: 0000000000000000
x13: ffff80003a058778 x12: ffff80003a058728
x11: ffff80003a058750 x10: 0000000000000000
x9 : 0000000000000006 x8 : ffff80003a825988
x7 : bbbbbbbbbbbbbbbb x6 : 0000000000000001
x5 : 0000000000000000 x4 : 0000000000000001
x3 : 0000000000000008 x2 : 0000000000000001
x1 : 6b6b6b6b6b6b6c03 x0 : 0000000000000000
Process sh (pid: 1784, stack limit = 0x        (ptrval))
Call trace:
 clear_bit+0x18/0x2c
 q6afe_remove+0x20/0x38
 apr_device_remove+0x30/0x70
 device_release_driver_internal+0x170/0x208
 device_release_driver+0x14/0x20
 bus_remove_device+0xcc/0x150
 device_del+0x10c/0x310
 device_unregister+0x1c/0x70
 apr_remove_device+0xc/0x18
 device_for_each_child+0x50/0x80
 apr_remove+0x18/0x20
 rpmsg_dev_remove+0x38/0x68
 device_release_driver_internal+0x170/0x208
 device_release_driver+0x14/0x20
 bus_remove_device+0xcc/0x150
 device_del+0x10c/0x310
 device_unregister+0x1c/0x70
 qcom_smd_remove_device+0xc/0x18
 device_for_each_child+0x50/0x80
 qcom_smd_unregister_edge+0x3c/0x70
 smd_subdev_remove+0x18/0x28
 rproc_stop+0x48/0xd8
 rproc_shutdown+0x60/0xe8
 state_store+0xbc/0xf8
 dev_attr_store+0x18/0x28
 sysfs_kf_write+0x3c/0x50
 kernfs_fop_write+0x118/0x1e0
 __vfs_write+0x18/0x110
 vfs_write+0xa4/0x1a8
 ksys_write+0x48/0xb0
 sys_write+0xc/0x18
 el0_svc_naked+0x30/0x34
Code: d2800022 8b400c21 f9800031 9ac32043 (c85f7c22)
---[ end trace 32020935775616a2 ]---

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: stable@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/platform.c

@@ -548,15 +548,16 @@ int of_platform_device_destroy(struct device *dev, void *data)
 	if (of_node_check_flag(dev->of_node, OF_POPULATED_BUS))
 		device_for_each_child(dev, NULL, of_platform_device_destroy);
 
+	of_node_clear_flag(dev->of_node, OF_POPULATED);
+	of_node_clear_flag(dev->of_node, OF_POPULATED_BUS);
+
 	if (dev->bus == &platform_bus_type)
 		platform_device_unregister(to_platform_device(dev));
 #ifdef CONFIG_ARM_AMBA
 	else if (dev->bus == &amba_bustype)
 		amba_device_unregister(to_amba_device(dev));
 #endif
 
-	of_node_clear_flag(dev->of_node, OF_POPULATED);
-	of_node_clear_flag(dev->of_node, OF_POPULATED_BUS);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(of_platform_device_destroy);