[patch 01/10] mm: bootmem: fix checking the bitmap when finally freeing bootmem

[Johannes Weiner]

From: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>

When bootmem releases an unaligned chunk of memory at the beginning of
a node to the page allocator, it iterates from that unaligned PFN but
checks an aligned word of the page bitmap.  The checked bits do not
correspond to the PFNs and, as a result, reserved pages can be freed.

Properly shift the bitmap word so that the lowest bit corresponds to
the starting PFN before entering the freeing loop.

This bug has been around since 41546c1 "bootmem: clean up
free_all_bootmem_core" (2.6.27) without known reports.

Signed-off-by: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 mm/bootmem.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/bootmem.c b/mm/bootmem.c
index 0131170..67872fc 100644
--- a/mm/bootmem.c
+++ b/mm/bootmem.c
@@ -203,6 +203,7 @@ static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
 		} else {
 			unsigned long off = 0;
 
+			vec >>= start & (BITS_PER_LONG - 1);
 			while (vec && off < BITS_PER_LONG) {
 				if (vec & 1) {
 					page = pfn_to_page(start + off);
-- 
1.7.10

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