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

[Eric DeVolder]

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();
> > +	}
> > +}
> ......