• Gavin Shan's avatar
    mm/sparse: remove index_init_lock · c1c95183
    Gavin Shan authored
    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: default avatarGavin Shan <shangw@linux.vnet.ibm.com>
    Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
    Cc: Michal Hocko <mhocko@suse.cz>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    c1c95183
sparse.c 20.3 KB