[PATCH] kernel/panic: Add "late_kdump" option for kdump in unstable condition

[Masami Hiramatsu]

Add a "late_kdump" option to run kdump after running panic
notifiers and dump kmsg. This can help rare situations which
kdump drops in failure because of unstable crashed kernel
or hardware failure (memory corruption on critical data/code),
or the 2nd kernel is broken by the 1st kernel (it's a broken
behavior, but who can guarantee that the "crashed" kernel
works correctly?).

Usage: add "late_kdump" to kernel boot option. That's all.

Note that this actually increases risks of the failure of
kdump. This option should be set only if you worry about
the rare case of kdump failure rather than increasing the
chance of success.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@xxxxxxxxxxx>
Cc: Satoru MORIYA <satoru.moriya.br@xxxxxxxxxxx>
Cc: Motohiro Kosaki <Motohiro.Kosaki@xxxxxxxxxxxxxx>
Cc: Takenori Nagano <t-nagano@xxxxxxxxxxxxx>
---
 Documentation/kernel-parameters.txt |    7 +++++++
 kernel/panic.c                      |   24 ++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 03e50b4..1ba58da 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2339,6 +2339,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			timeout < 0: reboot immediately
 			Format: <timeout>
 
+	late_kdump	Run kdump after running panic-notifiers and dumping
+			kmsg. This only for the users who doubt kdump always
+			succeeds in any situation.
+			Note that this also increases risks of kdump failure,
+			because some panic notifiers can make the crashed
+			kernel more unstable.
+
 	parkbd.port=	[HW] Parallel port number the keyboard adapter is
 			connected to, default is 0.
 			Format: <parport#>
diff --git a/kernel/panic.c b/kernel/panic.c
index d02fa9f..bba42b5 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -32,6 +32,7 @@ static unsigned long tainted_mask;
 static int pause_on_oops;
 static int pause_on_oops_flag;
 static DEFINE_SPINLOCK(pause_on_oops_lock);
+static bool late_kdump;
 
 int panic_timeout = CONFIG_PANIC_TIMEOUT;
 EXPORT_SYMBOL_GPL(panic_timeout);
@@ -112,9 +113,14 @@ void panic(const char *fmt, ...)
 	/*
 	 * If we have crashed and we have a crash kernel loaded let it handle
 	 * everything else.
-	 * Do we want to call this before we try to display a message?
+	 * If we want to call this after we try to display a message, pass
+	 * the "late_kdump" option to the kernel.
 	 */
-	crash_kexec(NULL);
+	if (!late_kdump)
+		crash_kexec(NULL);
+	else
+		pr_emerg("Warning: late_kdump option is set. Please DO NOT "
+			"report bugs about kdump failure with this option.\n");
 
 	/*
 	 * Note smp_send_stop is the usual smp shutdown function, which
@@ -131,6 +137,13 @@ void panic(const char *fmt, ...)
 
 	kmsg_dump(KMSG_DUMP_PANIC);
 
+	/*
+	 * If you doubt kdump always works perfectly in any situation,
+	 * "late_kdump" offers you to try kdump after running panic_notifier
+	 * and dumping kmsg.
+	 */
+	crash_kexec(NULL);
+
 	bust_spinlocks(0);
 
 	if (!panic_blink)
@@ -472,6 +485,13 @@ EXPORT_SYMBOL(__stack_chk_fail);
 core_param(panic, panic_timeout, int, 0644);
 core_param(pause_on_oops, pause_on_oops, int, 0644);
 
+static int __init setup_late_kdump(char *s)
+{
+	late_kdump = true;
+	return 0;
+}
+early_param("late_kdump", setup_late_kdump);
+
 static int __init oops_setup(char *s)
 {
 	if (!s)


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