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

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Date:   Fri, 17 Mar 2023 17:30:23 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Eric DeVolder <eric.devolder@...cle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, vgoyal@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH v19 2/7] crash: add generic infrastructure for crash
 hotplug support

On 03/16/23 at 10:47am, Eric DeVolder wrote:
> 
> 
> On 3/16/23 09:44, 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.
> > 
> > Thanks!
> > eric
> 
> Baoquan, as you are currently working through v19, please let me know when I
> should put out v20 with this and Sourabh's feedback.
> Thanks,
> eric

The overall serial looks good to me other than the nitpicks.