Re: [PATCH v10 4/8] crash: add generic infrastructure for crash hotplug support

[Eric DeVolder <eric.devolder@xxxxxxxxxx>]

On 8/8/22 04:30, Baoquan He wrote:
> On 07/21/22 at 02:17pm, Eric DeVolder wrote:
> > CPU and memory change notifications are received in order to
> > regenerate the elfcorehdr.
> >
> > To support cpu hotplug, a callback is registered to capture the
> > CPUHP_AP_ONLINE_DYN online and offline 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 notifiers call handle_hotplug_event()
> > which performs needed tasks and then dispatches the event to the
> > architecture specific arch_crash_handle_hotplug_event(). During the
> > process, the kexec_mutex is held.
> >
> > Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
> > ---
> >   include/linux/crash_core.h |  24 ++++++++
> >   include/linux/kexec.h      |   7 +++
> >   kernel/crash_core.c        | 118 +++++++++++++++++++++++++++++++++++++
> >   3 files changed, 149 insertions(+)
> >
> > diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> > index cb0f1916fbf5..c9705b6872e7 100644
> > --- a/include/linux/crash_core.h
> > +++ b/include/linux/crash_core.h
> > @@ -86,4 +86,28 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
> >   int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
> >   		unsigned long long *crash_size, unsigned long long *crash_base);
> >   
> > +#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
> > +#define KEXEC_CRASH_HP_INVALID_CPU		-1U
> > +
> > +struct kimage;
> > +#ifndef arch_map_crash_pages
> > +static inline void *arch_map_crash_pages(unsigned long paddr,
> > +		unsigned long size)
> > +{
> > +	return NULL;
> > +}
> > +#endif
> > +#ifndef arch_unmap_crash_pages
> > +static inline void arch_unmap_crash_pages(void **ptr) { }
> > +#endif
> > +#ifndef arch_crash_handle_hotplug_event
> > +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
> > +		unsigned int hp_action, unsigned int cpu)
> > +{
> > +}
> > +#endif
> > +
> >   #endif /* LINUX_CRASH_CORE_H */
> > diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> > index 5f4969cf3f4e..7694aa77b92b 100644
> > --- a/include/linux/kexec.h
> > +++ b/include/linux/kexec.h
> > @@ -340,6 +340,13 @@ struct kimage {
> >   	struct purgatory_info purgatory_info;
> >   #endif
> >   
> > +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> > +	bool hotplug_event;
> > +	unsigned int offlinecpu;
> > +	bool elfcorehdr_index_valid;
> > +	int elfcorehdr_index;
> > +#endif
> > +
> >   #ifdef CONFIG_IMA_KEXEC
> >   	/* Virtual address of IMA measurement buffer for kexec syscall */
> >   	void *ima_buffer;
> > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> > index 212d4dad0ec7..154ef532d45a 100644
> > --- a/kernel/crash_core.c
> > +++ b/kernel/crash_core.c
> > @@ -10,12 +10,16 @@
> >   #include <linux/utsname.h>
> >   #include <linux/vmalloc.h>
> >   #include <linux/kexec.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;
> > @@ -587,3 +591,117 @@ static int __init crash_save_vmcoreinfo_init(void)
> >   }
> >   
> >   subsys_initcall(crash_save_vmcoreinfo_init);
> > +
> > +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> > +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
> > +{
> > +	/* Obtain lock while changing crash information */
> > +	mutex_lock(&kexec_mutex);
> > +
> > +	/* Check kdump is loaded */
> > +	if (kexec_crash_image) {
> > +		struct kimage *image = kexec_crash_image;
> > +
> > +		pr_debug("crash hp: hp_action %u, cpu %u", hp_action, cpu);
>
> We don't need to check if it's cpu hotplug action here? Then for mem
> hotplug actions, we also get:
>                  "crash hp: hp_action 2, cpu 0"
> That cpu 0 will be confusing. And you forgot the line break.
>
> Can we do like this:
> 		pr_debug("crash hp: hp_action %u ", hp_action);
> 		if (hp_action == KEXEC_CRASH_HP_REMOVE_CPU ||
> 		    hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
> 			pr_debug("cpu %u \n", cpu);
>
> Other than this, the patch looks good to me.

OK, I'll make the changes you suggest, thanks!
eric

> > +
> > +		/*
> > +		 * When the struct kimage is alloced, it is wiped to zero, so
> > +		 * the elfcorehdr_index_valid defaults to false. 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_valid) {
> > +			unsigned char *ptr;
> > +			unsigned long mem, memsz;
> > +			unsigned int n;
> > +
> > +			for (n = 0; n < image->nr_segments; n++) {
> > +				mem = image->segment[n].mem;
> > +				memsz = image->segment[n].memsz;
> > +				ptr = arch_map_crash_pages(mem, memsz);
> > +				if (ptr) {
> > +					/* The segment containing elfcorehdr */
> > +					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
> > +						image->elfcorehdr_index = (int)n;
> > +						image->elfcorehdr_index_valid = true;
> > +					}
> > +				}
> > +				arch_unmap_crash_pages((void **)&ptr);
> > +			}
> > +		}
> > +
> > +		if (!image->elfcorehdr_index_valid) {
> > +			pr_err("crash hp: unable to locate elfcorehdr segment");
> > +			goto out;
> > +		}
> > +
> > +		/* Needed in order for the segments to be updated */
> > +		arch_kexec_unprotect_crashkres();
> > +
> > +		/* Flag to differentiate between normal load and hotplug */
> > +		image->hotplug_event = true;
> > +
> > +		/* Now invoke arch-specific update handler */
> > +		arch_crash_handle_hotplug_event(image, hp_action, cpu);
> > +
> > +		/* No longer handling a hotplug event */
> > +		image->hotplug_event = false;
> > +
> > +		/* Change back to read-only */
> > +		arch_kexec_protect_crashkres();
> > +	}
> > +
> > +out:
> > +	/* Release lock now that update complete */
> > +	mutex_unlock(&kexec_mutex);
> > +}
> > +
> > +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
> > +{
> > +	switch (val) {
> > +	case MEM_ONLINE:
> > +		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
> > +		break;
> > +
> > +	case MEM_OFFLINE:
> > +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
> > +		break;
> > +	}
> > +	return NOTIFY_OK;
> > +}
> > +
> > +static struct notifier_block crash_memhp_nb = {
> > +	.notifier_call = crash_memhp_notifier,
> > +	.priority = 0
> > +};
> > +
> > +static int crash_cpuhp_online(unsigned int cpu)
> > +{
> > +	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
> > +	return 0;
> > +}
> > +
> > +static int crash_cpuhp_offline(unsigned int cpu)
> > +{
> > +	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
> > +	return 0;
> > +}
> > +
> > +static int __init crash_hotplug_init(void)
> > +{
> > +	int result = 0;
> > +
> > +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> > +		register_memory_notifier(&crash_memhp_nb);
> > +
> > +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
> > +		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> > +						   "crash/cpuhp",
> > +						   crash_cpuhp_online,
> > +						   crash_cpuhp_offline);
> > +
> > +	return result;
> > +}
> > +
> > +subsys_initcall(crash_hotplug_init);
> > +#endif
> > --
> > 2.31.1

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