ppc/fadump: invoke kmsg_dump in fadump panic path

fadump is registered in panic_notifier_list and gets triggered before
kmsg_dump_desc() in the panic path. As a result, kmsg_dumpers such as
pstore are not executed during fadump crashes.

This is problematic because pstore provides a critical fallback mechanism
for crash analysis. When fadump fails to successfully reboot the system
or capture a dump, pstore logs may be the only available information from
the crashed kernel. Without invoking kmsg_dump_desc() in the fadump path,
we lose this valuable diagnostic data.

Invoke kmsg_dump_desc() from the fadump panic handler, but only when
fadump is actually registered (checked via should_fadump_crash()). This
ensures kmsg_dumpers are called without duplicating the call that occurs
later in panic() when fadump is not active.

The call is placed before crash_fadump() to ensure logs are captured
before the system attempts to trigger the firmware-assisted dump.

Reported-by: Shirisha G <shirisha@linux.ibm.com>
Suggested-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
Tested-by: Shirisha G <shirisha@linux.ibm.com>
Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260412113057.46090-1-shivangu@linux.ibm.com

Author: Shivang Upadhyay

arch/powerpc/kernel/setup-common.c

@@ -68,6 +68,7 @@
 #include <asm/kasan.h>
 #include <asm/mce.h>
 #include <asm/systemcfg.h>
+#include <linux/kmsg_dump.h>
 
 #include "setup.h"
 
@@ -741,6 +742,13 @@ static int ppc_panic_fadump_handler(struct notifier_block *this,
 	 */
 	hard_irq_disable();
 
+	/*
+	 * Invoke kmsg_dump (e.g., pstore) before crash_fadump() as fadump
+	 * runs before panic()'s kmsg_dump_desc() call.
+	 */
+	if (should_fadump_crash())
+		kmsg_dump_desc(KMSG_DUMP_PANIC, (char *)ptr);
+
 	/*
 	 * If firmware-assisted dump has been registered then trigger
 	 * its callback and let the firmware handles everything else.