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This change directly facilitates the udev rule for managing userspace re-loading of the crash kernel upon hot un/plug changes. For memory, this changeset introduces the crash_hotplug attribute to the /sys/devices/system/memory directory. For example: # udevadm info --attribute-walk /sys/devices/system/memory/memory81 looking at device '/devices/system/memory/memory81': KERNEL=="memory81" SUBSYSTEM=="memory" DRIVER=="" ATTR{online}=="1" ATTR{phys_device}=="0" ATTR{phys_index}=="00000051" ATTR{removable}=="1" ATTR{state}=="online" ATTR{valid_zones}=="Movable" looking at parent device '/devices/system/memory': KERNELS=="memory" SUBSYSTEMS=="" DRIVERS=="" ATTRS{auto_online_blocks}=="offline" ATTRS{block_size_bytes}=="8000000" ATTRS{crash_hotplug}=="1" For CPUs, this changeset introduces the crash_hotplug attribute to the /sys/devices/system/cpu directory. For example: # udevadm info --attribute-walk /sys/devices/system/cpu/cpu0 looking at device '/devices/system/cpu/cpu0': KERNEL=="cpu0" SUBSYSTEM=="cpu" DRIVER=="processor" ATTR{crash_notes}=="277c38600" ATTR{crash_notes_size}=="368" ATTR{online}=="1" looking at parent device '/devices/system/cpu': KERNELS=="cpu" SUBSYSTEMS=="" DRIVERS=="" ATTRS{crash_hotplug}=="1" ATTRS{isolated}=="" ATTRS{kernel_max}=="8191" ATTRS{nohz_full}==" (null)" ATTRS{offline}=="4-7" ATTRS{online}=="0-3" ATTRS{possible}=="0-7" ATTRS{present}=="0-3" With these sysfs attributes in place, it is possible to efficiently instruct the udev rule to skip crash kernel reloading. For example, the following is the proposed udev rule change for RHEL system 98-kexec.rules (as the first lines of the rule file): # The kernel handles updates to crash elfcorehdr for cpu and memory changes SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" When examined in the context of 98-kexec.rules, the above change tests if crash_hotplug is set, and if so, it skips the userspace initiated unload-then-reload of the crash kernel. Cpu and memory checks are separated in accordance with CONFIG_HOTPLUG_CPU and CONFIG_MEMORY_HOTPLUG kernel config options. If an architecture supports, for example, memory hotplug but not CPU hotplug, then the /sys/devices/system/memory/crash_hotplug attribute file is present, but the /sys/devices/system/cpu/crash_hotplug attribute file will NOT be present. Thus the udev rule will skip userspace processing of memory hot un/plug events, but the udev rule will evaluate false for CPU events, thus allowing userspace to process cpu hot un/plug events (ie the unload-then-reload of the kdump capture kernel). Signed-off-by: Eric DeVolder Reviewed-by: Sourabh Jain Acked-by: Baoquan He --- .../admin-guide/mm/memory-hotplug.rst | 8 ++++++++ Documentation/core-api/cpu_hotplug.rst | 18 ++++++++++++++++++ drivers/base/cpu.c | 14 ++++++++++++++ drivers/base/memory.c | 13 +++++++++++++ include/linux/kexec.h | 8 ++++++++ 5 files changed, 61 insertions(+) diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index 1b02fe5807cc..eb99d79223a3 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -291,6 +291,14 @@ The following files are currently defined: Availability depends on the CONFIG_ARCH_MEMORY_PROBE kernel configuration option. ``uevent`` read-write: generic udev file for device subsystems. +``crash_hotplug`` read-only: when changes to the system memory map + occur due to hot un/plug of memory, this file contains + '1' if the kernel updates the kdump capture kernel memory + map itself (via elfcorehdr), or '0' if userspace must update + the kdump capture kernel memory map. + + Availability depends on the CONFIG_MEMORY_HOTPLUG kernel + configuration option. ====================== ========================================================= .. note:: diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst index f75778d37488..0c8dc3fe5f94 100644 --- a/Documentation/core-api/cpu_hotplug.rst +++ b/Documentation/core-api/cpu_hotplug.rst @@ -750,6 +750,24 @@ will receive all events. A script like:: can process the event further. +When changes to the CPUs in the system occur, the sysfs file +/sys/devices/system/cpu/crash_hotplug contains '1' if the kernel +updates the kdump capture kernel list of CPUs itself (via elfcorehdr), +or '0' if userspace must update the kdump capture kernel list of CPUs. + +The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration +option. + +To skip userspace processing of CPU hot un/plug events for kdump +(ie the unload-then-reload to obtain a current list of CPUs), this sysfs +file can be used in a udev rule as follows: + + SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" + +For a cpu hot un/plug event, if the architecture supports kernel updates +of the elfcorehdr (which contains the list of CPUs), then the rule skips +the unload-then-reload of the kdump capture kernel. + Kernel Inline Documentations Reference ====================================== diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index 182c6122f815..f779894c6abe 100644 --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -282,6 +282,17 @@ static ssize_t print_cpus_nohz_full(struct device *dev, static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL); #endif +#ifdef CONFIG_HOTPLUG_CPU +#include +static ssize_t crash_hotplug_show(struct device *dev, + struct device_attribute *attr, + char *buf) +{ + return sprintf(buf, "%d\n", crash_hotplug_cpu_support()); +} +static DEVICE_ATTR_ADMIN_RO(crash_hotplug); +#endif + static void cpu_device_release(struct device *dev) { /* @@ -469,6 +480,9 @@ static struct attribute *cpu_root_attrs[] = { #ifdef CONFIG_NO_HZ_FULL &dev_attr_nohz_full.attr, #endif +#ifdef CONFIG_HOTPLUG_CPU + &dev_attr_crash_hotplug.attr, +#endif #ifdef CONFIG_GENERIC_CPU_AUTOPROBE &dev_attr_modalias.attr, #endif diff --git a/drivers/base/memory.c b/drivers/base/memory.c index b456ac213610..24b8ef4c830c 100644 --- a/drivers/base/memory.c +++ b/drivers/base/memory.c @@ -490,6 +490,16 @@ static ssize_t auto_online_blocks_store(struct device *dev, static DEVICE_ATTR_RW(auto_online_blocks); +#ifdef CONFIG_MEMORY_HOTPLUG +#include +static ssize_t crash_hotplug_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "%d\n", crash_hotplug_memory_support()); +} +static DEVICE_ATTR_RO(crash_hotplug); +#endif + /* * Some architectures will have custom drivers to do this, and * will not need to do it from userspace. The fake hot-add code @@ -889,6 +899,9 @@ static struct attribute *memory_root_attrs[] = { &dev_attr_block_size_bytes.attr, &dev_attr_auto_online_blocks.attr, +#ifdef CONFIG_MEMORY_HOTPLUG + &dev_attr_crash_hotplug.attr, +#endif NULL }; diff --git a/include/linux/kexec.h b/include/linux/kexec.h index f9bd46fcbd5d..0ac41f48de0b 100644 --- a/include/linux/kexec.h +++ b/include/linux/kexec.h @@ -509,6 +509,14 @@ static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { static inline void arch_crash_handle_hotplug_event(struct kimage *image) { } #endif +#ifndef crash_hotplug_cpu_support +static inline int crash_hotplug_cpu_support(void) { return 0; } +#endif + +#ifndef crash_hotplug_memory_support +static inline int crash_hotplug_memory_support(void) { return 0; } +#endif + #else /* !CONFIG_KEXEC_CORE */ struct pt_regs; struct task_struct;