Messages in this thread | | | Date | Tue, 16 Aug 2022 10:24:00 -0500 | Subject | Re: [PATCH v10 7/8] crash: memory and cpu hotplug sysfs attributes | From | Eric DeVolder <> |
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On 8/8/22 05:41, Baoquan He wrote: > On 07/21/22 at 02:17pm, Eric DeVolder wrote: >> This introduces the crash_hotplug attribute for memory and CPUs >> for use by userspace. 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 fail 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 <eric.devolder@oracle.com> > > LGTM, > > Acked-by: Baoquan He <bhe@redhat.com>
Awesome, thank you! eric
> >> --- >> .../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/crash_core.h | 6 ++++++ >> 5 files changed, 59 insertions(+) >> >> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst >> index 0f56ecd8ac05..494d7a63c543 100644 >> --- a/Documentation/admin-guide/mm/memory-hotplug.rst >> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst >> @@ -293,6 +293,14 @@ 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 c6f4ba2fb32d..13e33d098645 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 4c98849577d4..bd470236d9a2 100644 >> --- a/drivers/base/cpu.c >> +++ b/drivers/base/cpu.c >> @@ -293,6 +293,17 @@ 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 <linux/crash_core.h> >> +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 bc60c9cd3230..63c1754a52b6 100644 >> --- a/drivers/base/memory.c >> +++ b/drivers/base/memory.c >> @@ -483,6 +483,16 @@ static ssize_t auto_online_blocks_store(struct device *dev, >> >> static DEVICE_ATTR_RW(auto_online_blocks); >> >> +#ifdef CONFIG_MEMORY_HOTPLUG >> +#include <linux/crash_core.h> >> +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 >> @@ -887,6 +897,9 @@ 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/crash_core.h b/include/linux/crash_core.h >> index c9705b6872e7..3964e9924ea5 100644 >> --- a/include/linux/crash_core.h >> +++ b/include/linux/crash_core.h >> @@ -109,5 +109,11 @@ 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 >> >> #endif /* LINUX_CRASH_CORE_H */ >> -- >> 2.31.1 >> >
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