[PATCH v3 2/2] kernel/panic/kexec: fix "crash_kexec_post_notifiers" option issue in oops path

[HATAYAMA Daisuke]

The commit f06e5153f4ae2e2f3b0300f0e260e40cb7fefd45 introduced
"crash_kexec_post_notifiers" kernel boot option, which toggles
wheather panic() calls crash_kexec() before panic_notifiers and dump
kmsg or after.

The problem is that the commit overlooks panic_on_oops kernel boot
option. If it is enabled, crash_kexec() is called directly without
going through panic() in oops path.

To fix this issue, this patch adds a check to
"crash_kexec_post_notifiers" in the condition of kexec_should_crash().

Also, put a comment in kexec_should_crash() to explain not obvious
things on this patch.

Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
Acked-by: Baoquan He <bhe at redhat.com>
Tested-by: Hidehiro Kawai <hidehiro.kawai.ez at hitachi.com>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt at hitachi.com>
---
 include/linux/kernel.h |    3 +++
 kernel/kexec.c         |   11 +++++++++++
 kernel/panic.c         |    2 +-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3a5b48e..bd5331c 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -438,6 +438,9 @@ extern int panic_on_unrecovered_nmi;
 extern int panic_on_io_nmi;
 extern int panic_on_warn;
 extern int sysctl_panic_on_stackoverflow;
+
+extern bool crash_kexec_post_notifiers;
+
 /*
  * Only to be used by arch init code. If the user over-wrote the default
  * CONFIG_PANIC_TIMEOUT, honor it.
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 7a36fdc..a785c10 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -84,6 +84,17 @@ struct resource crashk_low_res = {
 
 int kexec_should_crash(struct task_struct *p)
 {
+	/*
+	 * If crash_kexec_post_notifiers is enabled, don't run
+	 * crash_kexec() here yet, which must be run after panic
+	 * notifiers in panic().
+	 */
+	if (crash_kexec_post_notifiers)
+		return 0;
+	/*
+	 * There are 4 panic() calls in do_exit() path, each of which
+	 * corresponds to each of these 4 conditions.
+	 */
 	if (in_interrupt() || !p->pid || is_global_init(p) || panic_on_oops)
 		return 1;
 	return 0;
diff --git a/kernel/panic.c b/kernel/panic.c
index 774614f..04e91ff 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -32,7 +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 crash_kexec_post_notifiers;
+bool crash_kexec_post_notifiers;
 int panic_on_warn __read_mostly;
 
 int panic_timeout = CONFIG_PANIC_TIMEOUT;