path: root/drivers
diff options
authorAlasdair G Kergon <>2005-11-21 21:32:34 -0800
committerLinus Torvalds <>2005-11-22 09:14:31 -0800
commit0e56822d30184d0da35a6ecc51f38c4ceb457a80 (patch)
treea9ee18ce0e724f16dde3c5c97af67fb3a92701f7 /drivers
parentc4cc66351a24da5feec298be2da59a85f68dd3ea (diff)
[PATCH] device-mapper: mirror log bitset fix
The linux bitset operators (test_bit, set_bit etc) work on arrays of "unsigned long". dm-log uses such bitsets but treats them as arrays of uint32_t, only allocating and zeroing a multiple of 4 bytes (as 'clean_bits' is a uint32_t). The patch below fixes this problem. The problem is specific to 64-bit big endian machines such as s390x or ppc-64 and can prevent pvmove terminating. In the simplest case, if "region_count" were (say) 30, then bitset_size (below) would be 4 and bitset_uint32_count would be 1. Thus the memory for this butset, after allocation and zeroing would be 0 0 0 0 X X X X On a bigendian 64bit machine, bit 0 for this bitset is in the 8th byte! (and every bit that dm-log would use would be in the X area). 0 0 0 0 X X X X ^ here which hasn't been cleared properly. As the dm-raid1 code only syncs and counts regions which have a 0 in the 'sync_bits' bitset, and only finishes when it has counted high enough, a large number of 1's among those 'X's will cause the sync to not complete. It is worth noting that the code uses the same bitsets for in-memory and on-disk logs. As these bitsets are host-endian and host-sized, this means that they cannot safely be moved between computers with Signed-off-by: Neil Brown <> Signed-off-by: Alasdair G Kergon <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'drivers')
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/md/dm-log.c b/drivers/md/dm-log.c
index e110655eabdb..a76349cb10a5 100644
--- a/drivers/md/dm-log.c
+++ b/drivers/md/dm-log.c
@@ -333,10 +333,10 @@ static int core_ctr(struct dirty_log *log, struct dm_target *ti,
lc->sync = sync;
- * Work out how many words we need to hold the bitset.
+ * Work out how many "unsigned long"s we need to hold the bitset.
bitset_size = dm_round_up(region_count,
- sizeof(*lc->clean_bits) << BYTE_SHIFT);
+ sizeof(unsigned long) << BYTE_SHIFT);
bitset_size >>= BYTE_SHIFT;
lc->bitset_uint32_count = bitset_size / 4;