Messages in this thread | | | Date | Fri, 7 Oct 2022 14:14:39 -0500 | Subject | Re: [PATCH v12 3/7] crash: add generic infrastructure for crash hotplug support | From | Eric DeVolder <> |
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On 10/3/22 12:51, Sourabh Jain wrote: > Hello Eric, > > On 10/09/22 02:35, 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@oracle.com> >> Acked-by: Baoquan He <bhe@redhat.com> >> --- >> include/linux/crash_core.h | 8 +++ >> include/linux/kexec.h | 26 +++++++ >> kernel/crash_core.c | 134 +++++++++++++++++++++++++++++++++++++ >> 3 files changed, 168 insertions(+) >> >> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h >> index de62a722431e..a270f8660538 100644 >> --- a/include/linux/crash_core.h >> +++ b/include/linux/crash_core.h >> @@ -84,4 +84,12 @@ 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; >> + >> #endif /* LINUX_CRASH_CORE_H */ >> diff --git a/include/linux/kexec.h b/include/linux/kexec.h >> index 4eefa631e0ae..9597b41136ec 100644 >> --- a/include/linux/kexec.h >> +++ b/include/linux/kexec.h >> @@ -374,6 +374,13 @@ 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; >> @@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g >> static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { } >> #endif >> +#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) >> +{ >> +} >> +#endif >> + >> #else /* !CONFIG_KEXEC_CORE */ >> struct pt_regs; >> struct task_struct; >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c >> index 8c648fd5897a..4b15d91f0b21 100644 >> --- a/kernel/crash_core.c >> +++ b/kernel/crash_core.c >> @@ -11,6 +11,8 @@ >> #include <linux/vmalloc.h> >> #include <linux/sizes.h> >> #include <linux/kexec.h> >> +#include <linux/memory.h> >> +#include <linux/cpuhotplug.h> >> #include <asm/page.h> >> #include <asm/sections.h> >> @@ -18,6 +20,7 @@ >> #include <crypto/sha1.h> >> #include "kallsyms_internal.h" >> +#include "kexec_internal.h" >> /* vmcoreinfo stuff */ >> unsigned char *vmcoreinfo_data; >> @@ -612,3 +615,134 @@ static int __init crash_save_vmcoreinfo_init(void) >> } >> subsys_initcall(crash_save_vmcoreinfo_init); >> + >> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG) >> +/* >> + * To accurately reflect hot un/plug changes, the elfcorehdr (which >> + * is passed to the crash kernel via the elfcorehdr= parameter) >> + * must be updated with the new list of CPUs and memories. >> + * >> + * In order to make changes to elfcorehdr, two conditions are needed: >> + * First, the segment containing the elfcorehdr must be large enough >> + * to permit a growing number of resources. The elfcorehdr memory is >> + * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES. >> + * Second, purgatory must explicitly exclude the elfcorehdr from the >> + * list of segments it checks (since the elfcorehdr changes and thus >> + * would require an update to purgatory itself to update the digest). >> + */ >> +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; >> + >> + if (hp_action == KEXEC_CRASH_HP_ADD_CPU || >> + hp_action == KEXEC_CRASH_HP_REMOVE_CPU) >> + pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu); >> + else >> + pr_debug("crash hp: hp_action %u\n", hp_action); >> + >> + /* >> + * When the struct kimage is allocated, 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); >> + >> + /* 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; > > Can we pass v (memory_notify) argument to arch_crash_handle_hotplug_event function > via handle_hotplug_event? > > Because the way memory hotplug is handled on PowerPC, it is hard to update the elfcorehdr > without memory_notify args. > > On PowePC memblock data structure is used to prepare elfcorehdr for kdump. Since the notifier > used for memory hotplug crash handler get initiated before the memblock data structure update > happens (as depicted below), the newly prepared elfcorehdr still holds the old memory regions. > So if the system crash with obsolete elfcorehdr, makedumpfile failed to collect vmcore. > > Sequence of actions done on PowerPC to server the memory hotplug: > > Initiate memory hot remove > | > v > offline pages > | > v > initiate memory notify call chain > for MEM_OFFLINE event. > (same is used for crash update) > | > v > prepare new elfcorehdr for kdump using > memblock data structure > | > v > update memblock data structure > > How passing memory_notify to arch crash hotplug handler will help? > > memory_notify holds the start PFN and page count, with that we can get > the base address and size of hot unplugged memory and can use the same > to avoid hot unplugged memeory region to get added in the elfcorehdr.. > > Thanks, > Sourabh Jain >
Sourabh, let's see what Baoquan thinks.
Baoquan, are you OK with this request? I once had these parameters to the crash hotplug handler and since they were unused at the time, you asked that I remove them, which I did.
To accommodate this, how about this:
static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu, unsigned long mem_start, unsigned long mem_size)
For CPU events, I would just pass zeros for mem_start/size. For memory events, I would pass KEXEC_CRASH_HP_INVALID_CPU.
Thanks, eric
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