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 <[email protected]> --- 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; } /* _______________________________________________ kexec mailing list [email protected] http://lists.infradead.org/mailman/listinfo/kexec
