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

[Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>]

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.chen@xxxxxxxxxxxx>
Signed-off-by: Mark-PK Tsai <Mark-PK.Tsai@xxxxxxxxxxxx>
Cc: YJ Chiang <yj.chiang@xxxxxxxxxxxx>
Cc: Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 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