On 03/16/23 at 09:44am, Eric DeVolder wrote:
>
>
> 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.
Yeah, setting image->hp_action = KEXEC_CRASH_HP_NONE in
do_kimage_alloc_init() will make code clearer. While I am wondering if
we don't initialie image->hp_action to KEXEC_CRASH_HP_NONE, and don't
set image->hp_action to KEXEC_CRASH_HP_NONE to actually delineate that a
hotplug event handling has completed, what will happen?
I mean you set image->hp_action to KEXEC_CRASH_HP_NONE explicitly, where
do you check if it should not be KEXEC_CRASH_HP_NONE? In
crash_handle_hotplug_event(), we took __kexec_lock and assign the passed
hp_action anyway.
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