[PATCH v2 1/1] kexec: dump kmessage before machine_kexec

[Pavel Tatashin]

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)

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>
---
 kernel/kexec_core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 4f8efc278aa7..e253c8b59145 100644
--- a/kernel/kexec_core.c
+++ b/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>
@@ -1180,6 +1181,7 @@ int kernel_kexec(void)
 		machine_shutdown();
 	}
 
+	kmsg_dump(KMSG_DUMP_SHUTDOWN);
 	machine_kexec(kexec_image);
 
 #ifdef CONFIG_KEXEC_JUMP
-- 
2.25.1