We are using memset() to improve performance when creating 1st and 2nd
bitmap. After doing round up the pfn_start and round down pfn_end, it's
possible that pfn_start_roundup is greater than pfn_end_round. A segment
fault could happen in that case because memset is taking roughly the
value of (pfn_end_round << 3 - pfn_start_roundup << 3 ), which is
negative, as its third argument.
So we can skip the memset if start is greater than end. It's safe
because we will set bit for the round up part and also round down part.
Actually this happens on my EFI virtual machine:
cat /proc/iomem:
00000000-00000fff : reserved
00001000-0009ffff : System RAM
000a0000-000bffff : PCI Bus 0000:00
000f0000-000fffff : System ROM
00100000-3d162017 : System RAM
01000000-015cab9b : Kernel code
015cab9c-019beb3f : Kernel data
01b4f000-01da9fff : Kernel bss
30000000-37ffffff : Crash kernel
3d162018-3d171e57 : System RAM
3d171e58-3d172017 : System RAM
3d172018-3d17ae57 : System RAM
3d17ae58-3dc10fff : System RAM
3dc11000-3dc18fff : reserved
3dc19000-3dc41fff : System RAM
3dc42000-3ddcefff : reserved
3ddcf000-3f7fefff : System RAM
3f7ff000-3f856fff : reserved
[..]
gdb ./makedumpfile core
(gdb) bt full
[..]
#1 0x000000000042775d in create_1st_bitmap_cyclic () at makedumpfile.c:4543
i = 0x5
pfn = 0x3d190
phys_start = 0x3d18ee58
phys_end = 0x3d18f018
pfn_start = 0x3d18e
pfn_end = 0x3d18f
pfn_start_roundup = 0x3d190
pfn_end_round = 0x3d188
pfn_start_byte = 0x7a32
pfn_end_byte = 0x7a31
[..]
(gdb) list makedumpfile.c:4543
4538 return FALSE;
4539
4540 pfn_start_byte = (pfn_start_roundup - info->cyclic_start_pfn) >> 3;
4541 pfn_end_byte = (pfn_end_round - info->cyclic_start_pfn) >> 3;
4542
4543 memset(info->partial_bitmap2 + pfn_start_byte,
4544 0xff,
4545 pfn_end_byte - pfn_start_byte);
4546
4547 for (pfn = pfn_end_round; pfn < pfn_end; ++pfn)
Signed-off-by: WANG Chao <chaowang at redhat.com>
---
makedumpfile.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/makedumpfile.c b/makedumpfile.c
index 23251a1..ef08d91 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -4435,11 +4435,13 @@ create_1st_bitmap_cyclic()
pfn_start_byte = (pfn_start_roundup - info->cyclic_start_pfn) >> 3;
pfn_end_byte = (pfn_end_round - info->cyclic_start_pfn) >> 3;
- memset(info->partial_bitmap1 + pfn_start_byte,
- 0xff,
- pfn_end_byte - pfn_start_byte);
+ if (pfn_start_byte < pfn_end_byte) {
+ memset(info->partial_bitmap1 + pfn_start_byte,
+ 0xff,
+ pfn_end_byte - pfn_start_byte);
- pfn_bitmap1 += (pfn_end_byte - pfn_start_byte) * BITPERBYTE;
+ pfn_bitmap1 += (pfn_end_byte - pfn_start_byte) * BITPERBYTE;
+ }
for (pfn = pfn_end_round; pfn < pfn_end; pfn++) {
if (set_bit_on_1st_bitmap(pfn))
@@ -4540,9 +4542,11 @@ initialize_2nd_bitmap_cyclic(void)
pfn_start_byte = (pfn_start_roundup - info->cyclic_start_pfn) >> 3;
pfn_end_byte = (pfn_end_round - info->cyclic_start_pfn) >> 3;
- memset(info->partial_bitmap2 + pfn_start_byte,
- 0xff,
- pfn_end_byte - pfn_start_byte);
+ if (pfn_start_byte < pfn_end_byte) {
+ memset(info->partial_bitmap2 + pfn_start_byte,
+ 0xff,
+ pfn_end_byte - pfn_start_byte);
+ }
for (pfn = pfn_end_round; pfn < pfn_end; ++pfn)
if (!set_bit_on_2nd_bitmap_for_kernel(pfn))
--
1.8.4.2
