[PATCH] slab: extended cpu notifiers

Patch from Dipankar Sarma  <dipankar@in.ibm.com>

This is Manfred's patch which provides a CPU_UP_PREPARE cpu notifier to
allow initialization of per_cpu data just before the cpu becomes fully
functional.

It also provides a facility for the CPU_UP_PREPARE handler to return
NOTIFY_BAD to signify that the CPU is not permitted to come up.  If
that happens, a CPU_UP_CANCELLED message is passed to all the handlers.

The patch also fixes a bogus NOFITY_BAD return from the softirq setup
code.

Patch has been acked by Rusty.

We need this mechanism in slab for starting per-cpu timers and for
allocating the per-cpu slab hgead arrays *before* the CPU has come up
and started using slab.

include/linux/notifier.h

@@ -60,7 +60,11 @@ extern int notifier_call_chain(struct notifier_block **n, unsigned long val, voi
 
 #define NETLINK_URELEASE	0x0001	/* Unicast netlink socket released */
 
-#define CPU_ONLINE	0x0002 /* CPU (unsigned)v coming up */
+#define CPU_ONLINE	0x0002 /* CPU (unsigned)v is up */
+#define CPU_UP_PREPARE	0x0003 /* CPU (unsigned)v coming up */
+#define CPU_UP_CANCELED	0x0004 /* CPU (unsigned)v NOT coming up */
+#define CPU_OFFLINE	0x0005 /* CPU (unsigned)v offline (still scheduling) */
+#define CPU_DEAD	0x0006 /* CPU (unsigned)v dead */
 
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */

kernel/cpu.c

@@ -29,6 +29,7 @@ void unregister_cpu_notifier(struct notifier_block *nb)
 int __devinit cpu_up(unsigned int cpu)
 {
 	int ret;
+	void *hcpu = (void *)(long)cpu;
 
 	if ((ret = down_interruptible(&cpucontrol)) != 0)
 		return ret;
@@ -37,18 +38,29 @@ int __devinit cpu_up(unsigned int cpu)
 		ret = -EINVAL;
 		goto out;
 	}
+	ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
+	if (ret == NOTIFY_BAD) {
+		printk("%s: attempt to bring up CPU %u failed\n",
+				__FUNCTION__, cpu);
+		ret = -EINVAL;
+		goto out_notify;
+	}
 
 	/* Arch-specific enabling code. */
 	ret = __cpu_up(cpu);
-	if (ret != 0) goto out;
+	if (ret != 0)
+		goto out_notify;
 	if (!cpu_online(cpu))
 		BUG();
 
 	/* Now call notifier in preparation. */
 	printk("CPU %u IS NOW UP!\n", cpu);
-	notifier_call_chain(&cpu_chain, CPU_ONLINE, (void *)(long)cpu);
+	notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 
- out:
+out_notify:
+	if (ret != 0)
+		notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
+out:
 	up(&cpucontrol);
 	return ret;
 }

kernel/softirq.c

@@ -316,9 +316,8 @@ static int __devinit cpu_callback(struct notifier_block *nfb,
 
 		while (!ksoftirqd_task(hotcpu))
 			yield();
-		return NOTIFY_OK;
  	}
-	return NOTIFY_BAD;
+	return NOTIFY_OK;
 }
 
 static struct notifier_block cpu_nfb = { &cpu_callback, NULL, 0 };