Re: [PATCH v7 4/8] crash: add generic infrastructure for crash hotplug support

[Baoquan He <bhe@redhat.com>]

On 04/26/22 at 09:36am, Sourabh Jain wrote:
> 
> On 15/04/22 03:59, Eric DeVolder wrote:
> > Hi Baoquan,
> > Inline comments below.
> > Thanks!
> > eric
> > 
> > On 4/13/22 21:45, Baoquan He wrote:
> > > On 04/13/22 at 12:42pm, Eric DeVolder wrote:
> > > > Upon CPU and memory changes, a generic crash_hotplug_handler()
> > > > dispatches the hot plug/unplug event to the architecture specific
> > > > arch_crash_hotplug_handler(). During the process, the kexec_mutex
> > > > is held.
> > > > 
> > > > To support cpu hotplug, a callback is registered to capture the
> > > > CPUHP_AP_ONLINE_DYN online and ofline events via
> > > > cpuhp_setup_state_nocalls().
> > > > 
> > > > To support memory hotplug, a notifier is registered to capture the
> > > > MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
> > > > 
> > > > The cpu callback and memory notifier then call crash_hotplug_handler()
> > > > to handle the hot plug/unplug event.
> > > > 
> > > > Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> > > > ---
> > > >   include/linux/kexec.h |  16 +++++++
> > > >   kernel/crash_core.c   | 101
> > > > ++++++++++++++++++++++++++++++++++++++++++
> > > >   2 files changed, 117 insertions(+)
> > > > 
> > > > diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> > > > index f93f2591fc1e..02daff1f47dd 100644
> > > > --- a/include/linux/kexec.h
> > > > +++ b/include/linux/kexec.h
> > > > @@ -306,6 +306,13 @@ struct kimage {
> > > >         /* Information for loading purgatory */
> > > >       struct purgatory_info purgatory_info;
> > > > +
> > > > +#ifdef CONFIG_CRASH_HOTPLUG
> > > > +    bool hotplug_event;
> > > > +    unsigned int offlinecpu;
> > > > +    bool elfcorehdr_index_valid;
> > > > +    int elfcorehdr_index;
> > > > +#endif
> > > >   #endif
> > > >     #ifdef CONFIG_IMA_KEXEC
> > > > @@ -322,6 +329,15 @@ struct kimage {
> > > >       unsigned long elf_load_addr;
> > > >   };
> > > >   +#ifdef CONFIG_CRASH_HOTPLUG
> > > > +void arch_crash_hotplug_handler(struct kimage *image,
> > > > +    unsigned int hp_action, unsigned int cpu);
> > > > +#define KEXEC_CRASH_HP_REMOVE_CPU   0
> > > > +#define KEXEC_CRASH_HP_ADD_CPU      1
> > > > +#define KEXEC_CRASH_HP_REMOVE_MEMORY 2
> > > > +#define KEXEC_CRASH_HP_ADD_MEMORY   3
> > > > +#endif /* CONFIG_CRASH_HOTPLUG */
> > > > +
> > > >   /* kexec interface functions */
> > > >   extern void machine_kexec(struct kimage *image);
> > > >   extern int machine_kexec_prepare(struct kimage *image);
> > > > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> > > > index 256cf6db573c..ecf746243ab2 100644
> > > > --- a/kernel/crash_core.c
> > > > +++ b/kernel/crash_core.c
> > > > @@ -9,12 +9,17 @@
> > > >   #include <linux/init.h>
> > > >   #include <linux/utsname.h>
> > > >   #include <linux/vmalloc.h>
> > > > +#include <linux/highmem.h>
> > > > +#include <linux/memory.h>
> > > > +#include <linux/cpuhotplug.h>
> > > >     #include <asm/page.h>
> > > >   #include <asm/sections.h>
> > > >     #include <crypto/sha1.h>
> > > >   +#include "kexec_internal.h"
> > > > +
> > > >   /* vmcoreinfo stuff */
> > > >   unsigned char *vmcoreinfo_data;
> > > >   size_t vmcoreinfo_size;
> > > > @@ -491,3 +496,99 @@ static int __init crash_save_vmcoreinfo_init(void)
> > > >   }
> > > >     subsys_initcall(crash_save_vmcoreinfo_init);
> > > > +
> > > > +#ifdef CONFIG_CRASH_HOTPLUG
> > > > +void __weak arch_crash_hotplug_handler(struct kimage *image,
> > > > +    unsigned int hp_action, unsigned int cpu)
> > > > +{
> > > > +    pr_warn("crash hp: %s not implemented", __func__);
> > > > +}
> > > > +
> > > > +static void crash_hotplug_handler(unsigned int hp_action,
> > > > +    unsigned int cpu)
> > > > +{
> > > > +    /* Obtain lock while changing crash information */
> > > > +    if (!mutex_trylock(&kexec_mutex))
> > > > +        return;
> > > > +
> > > > +    /* Check kdump is loaded */
> > > > +    if (kexec_crash_image) {
> > > > +        pr_debug("crash hp: hp_action %u, cpu %u", hp_action, cpu);
> > > > +
> > > > +        /* Needed in order for the segments to be updated */
> > > > +        arch_kexec_unprotect_crashkres();
> > > > +
> > > > +        /* Flag to differentiate between normal load and hotplug */
> > > > +        kexec_crash_image->hotplug_event = true;
> > > > +
> > > > +        /* Now invoke arch-specific update handler */
> > > > +        arch_crash_hotplug_handler(kexec_crash_image, hp_action, cpu);
> > > > +
> > > > +        /* No longer handling a hotplug event */
> > > > +        kexec_crash_image->hotplug_event = false;
> > > > +
> > > > +        /* Change back to read-only */
> > > > +        arch_kexec_protect_crashkres();
> > > > +    }
> > > > +
> > > > +    /* Release lock now that update complete */
> > > > +    mutex_unlock(&kexec_mutex);
> > > > +}
> > > > +
> > > > +#if defined(CONFIG_MEMORY_HOTPLUG)
> > > > +static int crash_memhp_notifier(struct notifier_block *nb,
> > > > +    unsigned long val, void *v)
> > > > +{
> > > > +    struct memory_notify *mhp = v;
> > > > +
> > > > +    switch (val) {
> > > > +    case MEM_ONLINE:
> > > > +        crash_hotplug_handler(KEXEC_CRASH_HP_ADD_MEMORY, -1U);
> > > We don't differentiate the memory add/remove, cpu add, except of cpu
> > > remove. Means the hp_action only differentiate cpu remove from the other
> > > action. Maybe only making two types?
> > > 
> > > #define KEXEC_CRASH_HP_REMOVE_CPU   0
> > > #define KEXEC_CRASH_HP_UPDATE_OTHER      1
> > > 
> > Sourabh Jain's work with PPC uses REMOVE_CPU, REMOVE_MEMORY, and
> > ADD_MEMORY.
> > Do you still want to consolidate these?
> 
> On PowerPC different actions are needed for CPU add and memory add/remove.
> For CPU add case only FDT is updated whereas for the memory hotplug we will
> be
> updating FDT and elfcorehdr.

I don't understand. For elfcorehdr updating, we only need regenerate it.
Do you update them different for memory add/remove?

What I saw is the added action for memory hotplug is only for message
printing. Is this really needed? And memory hotplug is even not
supported. Please correct me if I missed anything.

+       /* crash update on memory hotplug is not support yet */
+       if (hp_action == KEXEC_CRASH_HP_REMOVE_MEMORY || hp_action == KEXEC_CRASH_HP_ADD_MEMORY) {
+               pr_info_once("crash hp: crash update is not supported with memory hotplug\n");
+               return;
+       }


> 
> Ideally, I would prefer the crash hotplug handler to report all four actions
> separately.
> 
> Thanks,
> Sourabh Jain
>