After we created the clone volume, we need to zero the temp_snapshot,  cinder will write snapshot full and an error occurred in device-mapper. 

We can reproduce it .


OS: Ubuntu 12.04.2
Kernel: 3.2.0-40-virtual
LVM:
  LVM version:     2.02.66(2) (2010-05-20)
  Library version: 1.02.48 (2010-05-20)
  Driver version:  4.22.0

### 1. create vg

ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo truncate -s 10G stack-volumes
ubuntu@galaxy2:/mnt$ ll
total 24
drwxr-xr-x  3 root root        4096 Jul  5 07:09 ./
drwxr-xr-x 23 root root        4096 Jul  5 04:36 ../
drwx------  2 root root       16384 Jun 11 08:29 lost+found/
-rw-r--r--  1 root root 10737418240 Jul  5 07:09 stack-volumes
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo losetup -f --show stack-volumes 
/dev/loop0
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo pvcreate /dev/loop0
  Physical volume "/dev/loop0" successfully created
ubuntu@galaxy2:/mnt$ sudo vgcreate vg0  /dev/loop0
  Volume group "vg0" successfully created


### 2. create the origin volume and snapshots of the origin volume

ubuntu@galaxy2:/mnt$ sudo lvcreate -L 1G -n lv0 vg0
  Logical volume "lv0" created
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo lvs
  LV   VG   Attr   LSize Origin Snap%  Move Log Copy%  Convert
  lv0  vg0  -wi-a- 1.00g                                      
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo lvcreate -L 2G -n lv0_snapshot_0 --snapshot vg0/lv0 
  Logical volume "lv0_snapshot_0" created
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo lvcreate -L 1G -n lv0_snapshot_1 --snapshot vg0/lv0
  Logical volume "lv0_snapshot_1" created
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo lvs
  LV             VG   Attr   LSize Origin Snap%  Move Log Copy%  Convert
  lv0            vg0  owi-a- 1.00g                                      
  lv0_snapshot_0 vg0  swi-a- 2.00g lv0      0.00                        
  lv0_snapshot_1 vg0  swi-a- 1.00g lv0      0.00                        
ubuntu@galaxy2:/mnt$ 


### 3. zero the first snapshot

ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo dd if=/dev/zero of=/dev/mapper/vg0-lv0_snapshot_0 bs=1M count=1024 conv=fdatasync
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 124.915 s, 8.6 MB/s
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo lvs
  LV             VG   Attr   LSize Origin Snap%  Move Log Copy%  Convert
  lv0            vg0  owi-a- 1.00g                                      
  lv0_snapshot_0 vg0  swi-a- 2.00g lv0     50.20                        
  lv0_snapshot_1 vg0  swi-a- 1.00g lv0      0.00                        
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo lvdisplay vg0/lv0_snapshot_0
  --- Logical volume ---
  LV Name                /dev/vg0/lv0_snapshot_0
  VG Name                vg0
  LV UUID                KE7i1E-ZNCR-mc2Z-XNtQ-wiO3-tNjE-a8p2pT
  LV Write Access        read/write
  LV snapshot status     active destination for /dev/vg0/lv0
  LV Status              available
  # open                 0
  LV Size                1.00 GiB
  Current LE             256
  COW-table size         2.00 GiB
  COW-table LE           512
  Allocated to snapshot  50.20% 
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:1
   
ubuntu@galaxy2:/mnt$ 

### 4. zero the second snapshot

ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo dd if=/dev/zero of=/dev/mapper/vg0-lv0_snapshot_1 bs=1M count=1024 conv=fdatasync
dd: fdatasync failed for `/dev/mapper/vg0-lv0_snapshot_1': Input/output error
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 48.987 s, 21.9 MB/s
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo lvs
  /dev/dm-4: read failed after 0 of 4096 at 0: Input/output error
  LV             VG   Attr   LSize Origin Snap%  Move Log Copy%  Convert
  lv0            vg0  owi-a- 1.00g                                      
  lv0_snapshot_0 vg0  swi-a- 2.00g lv0     50.20                        
  lv0_snapshot_1 vg0  Swi-I- 1.00g lv0    100.00                        
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ sudo lvdisplay vg0/lv0_snapshot_1
  /dev/dm-4: read failed after 0 of 4096 at 0: Input/output error
  --- Logical volume ---
  LV Name                /dev/vg0/lv0_snapshot_1
  VG Name                vg0
  LV UUID                fO6gFN-c2b5-8bQO-TsKU-or9Q-SYEy-zlxY38
  LV Write Access        read/write
  LV snapshot status     INACTIVE destination for /dev/vg0/lv0
  LV Status              available
  # open                 0
  LV Size                1.00 GiB
  Current LE             256
  COW-table size         1.00 GiB
  COW-table LE           256
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:4
   
ubuntu@galaxy2:/mnt$ 
ubuntu@galaxy2:/mnt$ dmesg
[2069983.216951] device-mapper: snapshots: Invalidating snapshot: Unable to allocate exception.
[2070028.707217] quiet_error: 136 callbacks suppressed
[2070028.707223] Buffer I/O error on device dm-4, logical block 261122
[2070028.707236] Buffer I/O error on device dm-4, logical block 261123
[2070028.707240] lost page write due to I/O error on dm-4
......


###########

we notice that  it is 50.20% in Snap% after we wrote 1024MB data to the first snapshot.

2048 * 50.2% = 1028.096
1028.096 - 1024 = 4.096 

I think 4.096MB  is additional metadata of snapshot that need to be written to snapshot space along with 1024 MB data.
So, I think when we wrote 1024MB data to the second snapshot ,  data and additional data is more than snapshot size,  an error occurred in device-mapper.