Clearling bits on cyclic buffer can overrun the cyclic buffer
according to some combination of MAX_ORDER and cyclic buffer size.
The cyclic buffer size is corrected if possible.
Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
---
makedumpfile.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 70 insertions(+), 1 deletions(-)
diff --git a/makedumpfile.c b/makedumpfile.c
index 65b9fd7..18a1e0a 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -58,6 +58,7 @@ do { \
*ptr_long_table = value; \
} while (0)
+static void check_cyclic_buffer_overrun(void);
static void setup_page_is_buddy(void);
void
@@ -2832,6 +2833,9 @@ out:
!sadump_generate_elf_note_from_dumpfile())
return FALSE;
+ if (info->flag_cyclic && info->dump_level & DL_EXCLUDE_FREE)
+ check_cyclic_buffer_overrun();
+
} else {
if (!get_mem_map_without_mm())
return FALSE;
@@ -3669,6 +3673,61 @@ exclude_free_page(void)
}
/*
+ * Let C be a cyclic buffer size and B a bitmap size used for
+ * representing maximum block size managed by buddy allocator.
+ *
+ * For some combinations of C and B, clearing operation can overrun
+ * the cyclic buffer. Let's consider three cases.
+ *
+ * - If C == B, this is trivially safe.
+ *
+ * - If B > C, overrun can easily happen.
+ *
+ * - In case of C > B, if C mod B != 0, then there exist n > m > 0,
+ * B > b > 0 such that n x C = m x B + b. This means that clearing
+ * operation overruns cyclic buffer (B - b)-bytes in the
+ * combination of n-th cycle and m-th block.
+ *
+ * Note that C mod B != 0 iff (m x C) mod B != 0 for some m.
+ *
+ * If C == B, C mod B == 0 always holds. Again, if B > C, C mod B != 0
+ * always holds. Hence, it's always sufficient to check the condition
+ * C mod B != 0 in order to determine whether overrun can happen or
+ * not.
+ *
+ * The bitmap size used for maximum block size B is calculated from
+ * MAX_ORDER as:
+ *
+ * B := DIVIDE_UP((1 << (MAX_ORDER - 1)), BITS_PER_BYTE)
+ *
+ * Normally, MAX_ORDER is 11 at default. This is configurable through
+ * CONFIG_FORCE_MAX_ZONEORDER.
+ */
+static void
+check_cyclic_buffer_overrun(void)
+{
+ int max_order = ARRAY_LENGTH(zone.free_area);
+ int max_order_nr_pages = 1 << (max_order - 1);
+ unsigned long max_block_size = roundup(max_order_nr_pages, BITPERBYTE);
+
+ if (info->bufsize_cyclic %
+ roundup(max_order_nr_pages, BITPERBYTE)) {
+ unsigned long bufsize;
+
+ if (max_block_size > info->bufsize_cyclic) {
+ MSG("WARNING: some free pages are not filtered.\n");
+ return;
+ }
+
+ bufsize = info->bufsize_cyclic;
+ info->bufsize_cyclic = round(bufsize, max_block_size);
+
+ MSG("cyclic buffer size has been changed: %lu => %lu\n",
+ bufsize, info->bufsize_cyclic);
+ }
+}
+
+/*
* For the kernel versions from v2.6.15 to v2.6.17.
*/
static int
@@ -4013,8 +4072,18 @@ __exclude_unnecessary_pages(unsigned long mem_map,
&& info->page_is_buddy(flags, _mapcount, private, _count)) {
int i;
- for (i = 0; i < (1 << private); ++i)
+ for (i = 0; i < (1 << private); ++i) {
+ /*
+ * According to combination of
+ * MAX_ORDER and size of cyclic
+ * buffer, this clearing bit operation
+ * can overrun the cyclic buffer.
+ *
+ * See check_cyclic_buffer_overrun()
+ * for the detail.
+ */
clear_bit_on_2nd_bitmap_for_kernel(pfn + i);
+ }
pfn_free += i;
}
/*
