Re: [PATCH v19 2/7] crash: add generic infrastructure for crash hotplug support

[Eric DeVolder <eric.devolder@oracle.com>]

On 3/16/23 05:11, Baoquan He wrote:
> On 03/06/23 at 11:22am, Eric DeVolder wrote:
> ......
>> +static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
>> +{
>> +	/* Obtain lock while changing crash information */
>> +	if (kexec_trylock()) {
>> +
>> +		/* Check kdump is loaded */
>> +		if (kexec_crash_image) {
>> +			struct kimage *image = kexec_crash_image;
>> +
>> +			if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
>> +				hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
>> +				pr_debug("hp_action %u, cpu %u\n", hp_action, cpu);
>> +			else
>> +				pr_debug("hp_action %u\n", hp_action);
>> +
>> +			/*
>> +			 * When the struct kimage is allocated, the elfcorehdr_index
>> +			 * is set to -1. Find the segment containing the elfcorehdr,
>> +			 * if not already found. This works for both the kexec_load
>> +			 * and kexec_file_load paths.
>> +			 */
>> +			if (image->elfcorehdr_index < 0) {
>> +				unsigned long mem;
>> +				unsigned char *ptr;
>> +				unsigned int n;
>> +
>> +				for (n = 0; n < image->nr_segments; n++) {
>> +					mem = image->segment[n].mem;
>> +					ptr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
>> +					if (ptr) {
>> +						/* The segment containing elfcorehdr */
>> +						if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
>> +							image->elfcorehdr_index = (int)n;
>> +						}
>> +						kunmap_local(ptr);
>> +					}
>> +				}
>> +			}
>> +
>> +			if (image->elfcorehdr_index < 0) {
>> +				pr_err("unable to locate elfcorehdr segment");
>> +				goto out;
>> +			}
>> +
>> +			/* Needed in order for the segments to be updated */
>> +			arch_kexec_unprotect_crashkres();
>> +
>> +			/* Differentiate between normal load and hotplug update */
>> +			image->hp_action = hp_action;
>> +
>> +			/* Now invoke arch-specific update handler */
>> +			arch_crash_handle_hotplug_event(image);
>> +
>> +			/* No longer handling a hotplug event */
>> +			image->hp_action = KEXEC_CRASH_HP_NONE;
>> +			image->elfcorehdr_updated = true;
> 
> It's good to initialize the image->hp_action here, however where do
> you check it? Do you plan to add some check somewhere?

Hi Baoquan,
The hp_action member is initialized to 0 in do_image_alloc_init(). I've
mapped KEXEC_CRASH_HP_NONE onto 0 on purpose.

But the use of image->hp_action = KEXEC_CRASH_HP_NONE is to actually
delineate that a hotplug event handling has completed. You can see
imae->hp_action set to hp_action to capture what the triggering event
was, as passed into this function.

I will go ahead and set image->hp_action = KEXEC_CRASH_HP_NONE; explicitly
in do_kimage_alloc_init(), as that is done for the other crash hotplug members.

Thanks!
eric


> 
>> +
>> +			/* Change back to read-only */
>> +			arch_kexec_protect_crashkres();
>> +		}
>> +
>> +out:
>> +		/* Release lock now that update complete */
>> +		kexec_unlock();
>> +	}
>> +}
> ......
> 

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