Commit c1c95183 authored Jul 31, 2012 by Gavin Shan Committed by Linus Torvalds Jul 31, 2012

mm/sparse: remove index_init_lock



sparse_index_init() uses the index_init_lock spinlock to protect root
mem_section assignment.  The lock is not necessary anymore because the
function is called only during boot (during paging init which is executed
only from a single CPU) and from the hotplug code (by add_memory() via
arch_add_memory()) which uses mem_hotplug_mutex.

The lock was introduced by 28ae55c9 ("sparsemem extreme: hotplug
preparation") and sparse_index_init() was used only during boot at that
time.

Later when the hotplug code (and add_memory()) was introduced there was no
synchronization so it was possible to online more sections from the same
root probably (though I am not 100% sure about that).  The first
synchronization has been added by 6ad696d2 ("mm: allow memory hotplug and
hibernation in the same kernel") which was later replaced by the
mem_hotplug_mutex - 20d6c96b ("mem-hotplug: introduce
{un}lock_memory_hotplug()").

Let's remove the lock as it is not needed and it makes the code more
confusing.

[mhocko@suse.cz: changelog]
Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent db36a461

mm/sparse.c

+1 −13

Original line number	Diff line number	Diff line
		@@ -77,7 +77,6 @@ static struct mem_section noinline __init_refok *sparse_index_alloc(int nid)

		static int __meminit sparse_index_init(unsigned long section_nr, int nid)
		{
		static DEFINE_SPINLOCK(index_init_lock);
		unsigned long root = SECTION_NR_TO_ROOT(section_nr);
		struct mem_section *section;
		int ret = 0;
		@@ -88,20 +87,9 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid)
		section = sparse_index_alloc(nid);
		if (!section)
		return -ENOMEM;
		/*
		* This lock keeps two different sections from
		* reallocating for the same index
		*/
		spin_lock(&index_init_lock);

		if (mem_section[root]) {
		ret = -EEXIST;
		goto out;
		}

		mem_section[root] = section;
		out:
		spin_unlock(&index_init_lock);

		return ret;
		}
		#else /* !SPARSEMEM_EXTREME */

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