Clearling bits on cyclic buffer can overrun the cyclic buffer
according to some combination of MAX_ORDER and cyclic buffer size.
This patch warns this possibility but continues processing.
Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
---
makedumpfile.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 47 insertions(+), 1 deletions(-)
diff --git a/makedumpfile.c b/makedumpfile.c
index d1efc09..98eb640 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
@@ -2806,6 +2807,9 @@ 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;
@@ -3642,6 +3646,38 @@ exclude_free_page(void)
return TRUE;
}
+static void
+check_cyclic_buffer_overrun(void)
+{
+ int max_order = ARRAY_LENGTH(zone.free_area);
+ int max_order_nr_pages = 1 << (max_order - 1);
+
+ /*
+ * Let C be a cyclic buffer size and B a bitmap size used for
+ * representing maximum block size managed by buddy
+ * allocator. Then, if C mod B != 0, i.e., if there exists n >
+ * 0, B > b > 0 such that C = n x B + b, then clearing
+ * operation overruns cyclic buffer (B - b)-bytes.
+ *
+ * The bitmap size used for maximum block size B is calculated
+ * from MAX_ORDER as:
+ *
+ * B := ROUND_UP((1 << (MAX_ORDER - 1)), / BITS_PER_BYTE)
+ *
+ * Normally, MAX_ORDER is 11 at default. This is configurable
+ * through CONFIG_FORCE_MAX_ZONEORDER.
+ *
+ * Note that If MAX_ORDER is default 11, this overrun issue
+ * never happens. First, if MAX_ORDER is 11, B is 128
+ * bytes. Cyclic buffer size is always specified in kilobytes,
+ * i.e. C = 1024 x c for some c > 0. Hence, C mod B = 0
+ * because 1024 mod 128 = 0.
+ */
+ if (info->bufsize_cyclic %
+ roundup(max_order_nr_pages, BITPERBYTE))
+ MSG("Some free pages are not filtered.\n");
+}
+
/*
* For the kernel versions from v2.6.15 to v2.6.17.
*/
@@ -3978,8 +4014,18 @@ __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;
}
/*
