From: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> Subject: kexec: dump kmessage before machine_kexec kmsg_dump(KMSG_DUMP_SHUTDOWN) is called before machine_restart(), machine_halt(), machine_power_off(), the only one that is missing is machine_kexec(). The dmesg output that it contains can be used to study the shutdown performance of both kernel and systemd during kexec reboot. Here is example of dmesg data collected after kexec: root@dplat-cp22:~# cat /sys/fs/pstore/dmesg-ramoops-0 | tail ... <6>[ 70.914592] psci: CPU3 killed (polled 0 ms) <5>[ 70.915705] CPU4: shutdown <6>[ 70.916643] psci: CPU4 killed (polled 4 ms) <5>[ 70.917715] CPU5: shutdown <6>[ 70.918725] psci: CPU5 killed (polled 0 ms) <5>[ 70.919704] CPU6: shutdown <6>[ 70.920726] psci: CPU6 killed (polled 4 ms) <5>[ 70.921642] CPU7: shutdown <6>[ 70.922650] psci: CPU7 killed (polled 0 ms) Link: https://lkml.kernel.org/r/20210319192326.146000-2-pasha.tatashin@xxxxxxxxxx Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Petr Mladek <pmladek@xxxxxxxx> Reviewed-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx> Acked-by: Baoquan He <bhe@xxxxxxxxxx> Reviewed-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx> Cc: James Morris <jmorris@xxxxxxxxx> Cc: Sasha Levin <sashal@xxxxxxxxxx> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> Cc: Anton Vorontsov <anton@xxxxxxxxxx> Cc: Colin Cross <ccross@xxxxxxxxxxx> Cc: Tony Luck <tony.luck@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/kexec_core.c | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/kexec_core.c~kexec-dump-kmessage-before-machine_kexec +++ a/kernel/kexec_core.c @@ -37,6 +37,7 @@ #include <linux/compiler.h> #include <linux/hugetlb.h> #include <linux/objtool.h> +#include <linux/kmsg_dump.h> #include <asm/page.h> #include <asm/sections.h> @@ -1179,6 +1180,7 @@ int kernel_kexec(void) machine_shutdown(); } + kmsg_dump(KMSG_DUMP_SHUTDOWN); machine_kexec(kexec_image); #ifdef CONFIG_KEXEC_JUMP _
