sparse_index_init uses index_init_lock spinlock to protect root
mem_section assignment. The lock is not necessary anymore because the
function is called only during the 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 has been 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 has been 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@xxxxxxx: changelog]
Signed-off-by: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
---
mm/sparse.c | 14 +-------------
1 files changed, 1 insertions(+), 13 deletions(-)
diff --git a/mm/sparse.c b/mm/sparse.c
index 51950de..40b1100 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 */
--
1.7.5.4
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