[PATCH] mm/sparse: fix memory leak of sparsemap_buf in aliged memory

[Lecopzer Chen]

sparse_buffer_alloc(size) get size of memory from sparsemap_buf after
being aligned with the size. However, the size is at least
PAGE_ALIGN(sizeof(struct page) * PAGES_PER_SECTION) and usually larger
than PAGE_SIZE.
Also, the Sparse_buffer_fini() only frees memory between
sparsemap_buf and sparsemap_buf_end, since sparsemap_buf may be changed
by PTR_ALIGN() first, the aligned space before sparsemap_buf is
wasted and no one will touch it.

In our ARM32 platform (without SPARSEMEM_VMEMMAP)
  Sparse_buffer_init
    Reserve d359c000 - d3e9c000 (9M)
  Sparse_buffer_alloc
    Alloc   d3a00000 - d3E80000 (4.5M)
  Sparse_buffer_fini
    Free    d3e80000 - d3e9c000 (~=100k)
 The reserved memory between d359c000 - d3a00000 (~=4.4M) is unfreed.

In ARM64 platform (with SPARSEMEM_VMEMMAP)

  sparse_buffer_init
    Reserve ffffffc07d623000 - ffffffc07f623000 (32M)
  Sparse_buffer_alloc
    Alloc   ffffffc07d800000 - ffffffc07f600000 (30M)
  Sparse_buffer_fini
    Free    ffffffc07f600000 - ffffffc07f623000 (140K)
 The reserved memory between ffffffc07d623000 - ffffffc07d800000
 (~=1.9M) is unfreed.

Let explicit free redundant aligned memory.

Signed-off-by: Lecopzer Chen <lecopzer.c...@mediatek.com>
Signed-off-by: Mark-PK Tsai <mark-pk.t...@mediatek.com>
Cc: YJ Chiang <yj.chi...@mediatek.com>
Cc: Lecopzer Chen <lecopzer.c...@mediatek.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Pavel Tatashin <pasha.tatas...@oracle.com>
Cc: Oscar Salvador <osalva...@suse.de>
Cc: Michal Hocko <mho...@suse.com>
Cc: Mike Rapoport <r...@linux.ibm.com>
Cc: linux-kernel@vger.kernel.org
---
 mm/sparse.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index fd13166949b5..2b3b5be85120 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -428,6 +428,12 @@ struct page __init *sparse_mem_map_populate(unsigned long 
pnum, int nid,
 static void *sparsemap_buf __meminitdata;
 static void *sparsemap_buf_end __meminitdata;
 
+static inline void __init sparse_buffer_free(unsigned long size)
+{
+       WARN_ON(!sparsemap_buf || size == 0);
+       memblock_free_early(__pa(sparsemap_buf), size);
+}
+
 static void __init sparse_buffer_init(unsigned long size, int nid)
 {
        phys_addr_t addr = __pa(MAX_DMA_ADDRESS);
@@ -444,7 +450,7 @@ static void __init sparse_buffer_fini(void)
        unsigned long size = sparsemap_buf_end - sparsemap_buf;
 
        if (sparsemap_buf && size > 0)
-               memblock_free_early(__pa(sparsemap_buf), size);
+               sparse_buffer_free(size);
        sparsemap_buf = NULL;
 }
 
@@ -456,8 +462,12 @@ void * __meminit sparse_buffer_alloc(unsigned long size)
                ptr = PTR_ALIGN(sparsemap_buf, size);
                if (ptr + size > sparsemap_buf_end)
                        ptr = NULL;
-               else
+               else {
+                       /* Free redundant aligned space */
+                       if ((unsigned long)(ptr - sparsemap_buf) > 0)
+                               sparse_buffer_free((unsigned long)(ptr - 
sparsemap_buf));
                        sparsemap_buf = ptr + size;
+               }
        }
        return ptr;
 }
-- 
2.18.0