[PATCH] sched: hotplug add a CPU_DOWN_FAILED notifier

Introduce CPU_DOWN_FAILED notifier, so we can cope with a failure after a
CPU_DOWN_PREPARE notice.

This fixes 3/8 "add CPU_DOWN_PREPARE notifier" to be useful
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/notifier.h

@@ -68,7 +68,8 @@ extern int notifier_call_chain(struct notifier_block **n, unsigned long val, voi
 #define CPU_UP_PREPARE		0x0003 /* CPU (unsigned)v coming up */
 #define CPU_UP_CANCELED		0x0004 /* CPU (unsigned)v NOT coming up */
 #define CPU_DOWN_PREPARE	0x0005 /* CPU (unsigned)v going down */
-#define CPU_DEAD		0x0006 /* CPU (unsigned)v dead */
+#define CPU_DOWN_FAILED		0x0006 /* CPU (unsigned)v NOT going down */
+#define CPU_DEAD		0x0007 /* CPU (unsigned)v dead */
 
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */

kernel/cpu.c

@@ -141,6 +141,11 @@ int cpu_down(unsigned int cpu)
 
 	p = __stop_machine_run(take_cpu_down, NULL, cpu);
 	if (IS_ERR(p)) {
+		/* CPU didn't die: tell everyone.  Can't complain. */
+		if (notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
+				(void *)(long)cpu) == NOTIFY_BAD)
+			BUG();
+
 		err = PTR_ERR(p);
 		goto out_allowed;
 	}