Re: [PATCH v6] powerpc/kexec_file: use current CPU info while setting up FDT

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 28/04/21 6:02 am, Tyrel Datwyler wrote:
> On 4/26/21 9:51 PM, Sourabh Jain wrote:
>> kexec_file_load uses initial_boot_params in setting up the device-tree
>> for the kernel to be loaded. Though initial_boot_params holds info
>> about CPUs at the time of boot, it doesn't account for hot added CPUs.
>>
>> So, kexec'ing with kexec_file_load syscall would leave the kexec'ed
>> kernel with inaccurate CPU info. Also, if kdump kernel is loaded with
>> kexec_file_load syscall and the system crashes on a hot added CPU,
>> capture kernel hangs failing to identify the boot CPU.
>>
>>   Kernel panic - not syncing: sysrq triggered crash
>>   CPU: 24 PID: 6065 Comm: echo Kdump: loaded Not tainted 5.12.0-rc5upstream #54
>>   Call Trace:
>>   [c0000000e590fac0] [c0000000007b2400] dump_stack+0xc4/0x114 (unreliable)
>>   [c0000000e590fb00] [c000000000145290] panic+0x16c/0x41c
>>   [c0000000e590fba0] [c0000000008892e0] sysrq_handle_crash+0x30/0x40
>>   [c0000000e590fc00] [c000000000889cdc] __handle_sysrq+0xcc/0x1f0
>>   [c0000000e590fca0] [c00000000088a538] write_sysrq_trigger+0xd8/0x178
>>   [c0000000e590fce0] [c0000000005e9b7c] proc_reg_write+0x10c/0x1b0
>>   [c0000000e590fd10] [c0000000004f26d0] vfs_write+0xf0/0x330
>>   [c0000000e590fd60] [c0000000004f2aec] ksys_write+0x7c/0x140
>>   [c0000000e590fdb0] [c000000000031ee0] system_call_exception+0x150/0x290
>>   [c0000000e590fe10] [c00000000000ca5c] system_call_common+0xec/0x278
>>   --- interrupt: c00 at 0x7fff905b9664
>>   NIP:  00007fff905b9664 LR: 00007fff905320c4 CTR: 0000000000000000
>>   REGS: c0000000e590fe80 TRAP: 0c00   Not tainted  (5.12.0-rc5upstream)
>>   MSR:  800000000280f033 <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 28000242
>>         XER: 00000000
>>   IRQMASK: 0
>>   GPR00: 0000000000000004 00007ffff5fedf30 00007fff906a7300 0000000000000001
>>   GPR04: 000001002a7355b0 0000000000000002 0000000000000001 00007ffff5fef616
>>   GPR08: 0000000000000001 0000000000000000 0000000000000000 0000000000000000
>>   GPR12: 0000000000000000 00007fff9073a160 0000000000000000 0000000000000000
>>   GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>>   GPR20: 0000000000000000 00007fff906a4ee0 0000000000000002 0000000000000001
>>   GPR24: 00007fff906a0898 0000000000000000 0000000000000002 000001002a7355b0
>>   GPR28: 0000000000000002 00007fff906a1790 000001002a7355b0 0000000000000002
>>   NIP [00007fff905b9664] 0x7fff905b9664
>>   LR [00007fff905320c4] 0x7fff905320c4
>>   --- interrupt: c00
>>
>> To avoid this from happening, extract current CPU info from of_root
>> device node and use it for setting up the fdt in kexec_file_load case.
>>
>> Fixes: 6ecd0163d360 ("powerpc/kexec_file: Add appropriate regions for memory reserve map")
>>
>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
>> Reviewed-by: Hari Bathini <hbathini@linux.ibm.com>
>> Cc: <stable@vger.kernel.org>
>> ---
>>   arch/powerpc/kexec/file_load_64.c | 88 +++++++++++++++++++++++++++++++
>>   1 file changed, 88 insertions(+)
>>
>>   ---
>> Changelog:
>>
>> v1 -> v5
>>    - https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-April/227950.html
>>
>> v5 -> v6
>>    - use exiting macro (for_each_property_of_node) to loop through all
>>      properties of a node.
>>    - removed devtree_lock while accessing the node properties.
>>    - function name update, add_node_prop to add_node_props.
>>   ---
>>
>> diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
>> index 02b9e4d0dc40..4f7d4c10f939 100644
>> --- a/arch/powerpc/kexec/file_load_64.c
>> +++ b/arch/powerpc/kexec/file_load_64.c
>> @@ -960,6 +960,89 @@ unsigned int kexec_fdt_totalsize_ppc64(struct kimage *image)
>>   	return fdt_size;
>>   }
>>
>> +/**
>> + * add_node_props - Reads node properties from device node structure and add
>> + *                  them to fdt.
>> + * @fdt:            Flattened device tree of the kernel
>> + * @node_offset:    offset of the node to add a property at
>> + * @dn:             device node pointer
>> + *
>> + * Returns 0 on success, negative errno on error.
>> + */
>> +static int add_node_props(void *fdt, int node_offset, const struct device_node *dn)
>> +{
>> +	int ret = 0;
>> +	struct property *pp;
>> +
>> +	if (!dn)
>> +		return -EINVAL;
>> +
>> +	for_each_property_of_node(dn, pp) {
>> +		ret = fdt_setprop(fdt, node_offset, pp->name, pp->value, pp->length);
>> +		if (ret < 0) {
>> +			pr_err("Unable to add %s property: %s\n", pp->name, fdt_strerror(ret));
>> +			return ret;
>> +		}
>> +	}
>> +	return ret;
>> +}
>> +
>> +/**
>> + * update_cpus_node - Update cpus node of flattened device tree using of_root
>> + *                    device node.
>> + * @fdt:              Flattened device tree of the kernel.
>> + *
>> + * Returns 0 on success, negative errno on error.
>> + */
>> +static int update_cpus_node(void *fdt)
>> +{
>> +	struct device_node *cpus_node, *dn;
>> +	int cpus_offset, cpus_subnode_offset, ret = 0;
>> +
>> +	cpus_offset = fdt_path_offset(fdt, "/cpus");
>> +	if (cpus_offset < 0 && cpus_offset != -FDT_ERR_NOTFOUND) {
>> +		pr_err("Malformed device tree: error reading /cpus node: %s\n",
>> +		       fdt_strerror(cpus_offset));
>> +		return cpus_offset;
>> +	}
>> +
>> +	if (cpus_offset > 0) {
>> +		ret = fdt_del_node(fdt, cpus_offset);
>> +		if (ret < 0) {
>> +			pr_err("Error deleting /cpus node: %s\n", fdt_strerror(ret));
>> +			return -EINVAL;
>> +		}
>> +	}
>> +
>> +	/* Add cpus node to fdt */
>> +	cpus_offset = fdt_add_subnode(fdt, fdt_path_offset(fdt, "/"), "cpus");
>> +	if (cpus_offset < 0) {
>> +		pr_err("Error creating /cpus node: %s\n", fdt_strerror(cpus_offset));
>> +		return -EINVAL;
>> +	}
>> +
>> +	/* Add cpus node properties */
>> +	cpus_node = of_find_node_by_path("/cpus");
> Pretty sure that of_find_node_by_path() returns a device_node with its refcount
> incremented.
>
>> +	ret = add_node_props(fdt, cpus_offset, cpus_node);
> Need a of_node_put(cpus_node) here.
>
> Thanks for the review Tyrel. updated in v7.
>
> - Sourabh