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>

1 files changed, 1 insertions, 13 deletions

diff --git a/mm/sparse.c b/mm/sparse.c
index 42ca0ea9af1..fac95f2888f 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -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 */