Re: [RFC PATCH] memory-hotplug: Add memblock_state notifier

Hi,

On Mon, Jul 23, 2012 at 05:08:04PM +0800, Wen Congyang wrote:

quoted

+static int memblock_state_notifier_nb(struct notifier_block *nb, unsigned long
+		val, void *v)
+{
+	struct memory_notify *arg = (struct memory_notify *)v;
+	struct memory_block *mem = NULL;
+	struct mem_section *ms;
+	unsigned long section_nr;
+
+	section_nr = pfn_to_section_nr(arg->start_pfn);
+	ms = __nr_to_section(section_nr);
+	mem = find_memory_block(ms);
+	if (!mem)
+		goto out;

we may offline more than one memory block.

thanks, you are right.

quoted

+
+	switch (val) {
+	case MEM_GOING_OFFLINE:
+	case MEM_OFFLINE:
+	case MEM_GOING_ONLINE:
+	case MEM_ONLINE:
+	case MEM_CANCEL_ONLINE:
+	case MEM_CANCEL_OFFLINE:
+		mem->state = val;

mem->state is protected by the lock mem->state_mutex, so if you want to
update the state, you must lock mem->state_mutex. But you cannot lock it
here, because it may cause deadlock:

acpi_memhotplug                           sysfs interface
===============================================================================
                                          memory_block_change_state()
                                              lock mem->state_mutex
                                              memory_block_action()
offline_pages()
    lock_memory_hotplug()
                                                  offline_memory()
                                                      lock_memory_hotplug() // block
    memory_notify()
        memblock_state_notifier_nb()
===============================================================================

good point. Maybe if memory_hotplug_lock and state_mutex locks are acquired in
the same order in the 2 code paths, this could be avoided.

I'm writing another patch to fix it.

ok, I 'll test.
thanks,

- Vasilis

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