On Tue, Apr 22, 2025 at 02:31:42PM +0300, Eugen Hristev wrote: > kmemdump is a mechanism which allows the kernel to mark specific memory > areas for dumping or specific backend usage. > Once regions are marked, kmemdump keeps an internal list with the regions > and registers them in the backend. > Further, depending on the backend driver, these regions can be dumped using > firmware or different hardware block. > Regions being marked beforehand, when the system is up and running, there > is no need nor dependency on a panic handler, or a working kernel that can > dump the debug information. > The kmemdump approach works when pstore, kdump, or another mechanism do not. > Pstore relies on persistent storage, a dedicated RAM area or flash, which > has the disadvantage of having the memory reserved all the time, or another > specific non volatile memory. Some devices cannot keep the RAM contents on > reboot so ramoops does not work. Some devices do not allow kexec to run > another kernel to debug the crashed one. > For such devices, that have another mechanism to help debugging, like > firmware, kmemdump is a viable solution. > > kmemdump can create a core image, similar with /proc/vmcore, with only > the registered regions included. This can be loaded into crash tool/gdb and > analyzed. > To have this working, specific information from the kernel is registered, > and this is done at kmemdump init time, no need for the kmemdump user to > do anything. > > The implementation is based on the initial Pstore/directly mapped zones > published as an RFC here: > https://lore.kernel.org/all/20250217101706.2104498-1-eugen.hristev@xxxxxxxxxx/ > > The back-end implementation for qcom_smem is based on the minidump > patch series and driver written by Mukesh Ojha, thanks: > https://lore.kernel.org/lkml/20240131110837.14218-1-quic_mojha@xxxxxxxxxxx/ > > I appreciate the feedback on this series, I know it is a longshot, and there > is a lot to improve, but I hope I am on the right track. > > Thanks, > Eugen > > PS. Here is how crash tool reports the dump: > > KERNEL: /home/eugen/linux-minidump/vmlinux [TAINTED] > DUMPFILE: /home/eugen/eee Can you please describe the steps taken to get acquire/generate this file and how to invoke crash? Regards, Bjorn > CPUS: 8 [OFFLINE: 7] > DATE: Thu Jan 1 02:00:00 EET 1970 > UPTIME: 00:00:28 > NODENAME: qemuarm64 > RELEASE: 6.14.0-rc5-next-20250303-00014-g011eb2aaf7b6-dirty > VERSION: #169 SMP PREEMPT Thu Apr 17 14:12:21 EEST 2025 > MACHINE: aarch64 (unknown Mhz) > MEMORY: 0 > PANIC: "" > > crash> log > [ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd4b2] > [ 0.000000] Linux version 6.14.0-rc5-next-20250303-00014-g011eb2aaf7b6-dirty (eugen@eugen-station) (aarch64-none-linux-gnu-gcc (Arm GNU Toolchain 13.3.Rel1 (Build arm-13.24)) 13.3.1 20240614, GNU ld (Arm GNU Toolchain 13.3.Rel1 (Build arm-13.24)) 2.42.0.20240614) #169 SMP PREEMPT Thu Apr 17 14:12:21 EEST 2025 > [ 0.000000] KASLR enabled > [...] > > Eugen Hristev (14): > Documentation: add kmemdump > kmemdump: introduce kmemdump > kmemdump: introduce qcom-md backend driver > soc: qcom: smem: add minidump device > Documentation: kmemdump: add section for coreimage ELF > kmemdump: add coreimage ELF layer > printk: add kmsg_kmemdump_register > kmemdump: coreimage: add kmsg registration > genirq: add irq_kmemdump_register > kmemdump: coreimage: add irq registration > panic: add panic_kmemdump_register > kmemdump: coreimage: add panic registration > sched: add sched_kmemdump_register > kmemdump: coreimage: add sched registration > > Documentation/debug/index.rst | 17 ++ > Documentation/debug/kmemdump.rst | 83 +++++ > drivers/Kconfig | 2 + > drivers/Makefile | 2 + > drivers/debug/Kconfig | 39 +++ > drivers/debug/Makefile | 5 + > drivers/debug/kmemdump.c | 197 ++++++++++++ > drivers/debug/kmemdump_coreimage.c | 293 ++++++++++++++++++ > drivers/debug/qcom_md.c | 467 +++++++++++++++++++++++++++++ > drivers/soc/qcom/smem.c | 10 + > include/linux/irqnr.h | 1 + > include/linux/kmemdump.h | 77 +++++ > include/linux/kmsg_dump.h | 6 + > include/linux/panic.h | 1 + > include/linux/sched.h | 1 + > kernel/irq/irqdesc.c | 7 + > kernel/panic.c | 8 + > kernel/printk/printk.c | 13 + > kernel/sched/core.c | 7 + > 19 files changed, 1236 insertions(+) > create mode 100644 Documentation/debug/index.rst > create mode 100644 Documentation/debug/kmemdump.rst > create mode 100644 drivers/debug/Kconfig > create mode 100644 drivers/debug/Makefile > create mode 100644 drivers/debug/kmemdump.c > create mode 100644 drivers/debug/kmemdump_coreimage.c > create mode 100644 drivers/debug/qcom_md.c > create mode 100644 include/linux/kmemdump.h > > -- > 2.43.0 >
