Issue

• Experience kernel crashes since we do simple snapshots for backup of LVs. The kernel log message in all three cases was:

2.6.32-504.1.3.el6.x86_64: RIP: 0010:[<ffffffffa0477ff7>]  [<ffffffffa0477ff7>] persistent_commit_exception+0x157/0x160 [dm_snapshot]
2.6.32-431.20.3.el6.x86_64: RIP: 0010:[<ffffffffa03c1e3f>]  [<ffffffffa03c1e3f>] persistent_commit_exception+0x14f/0x160 [dm_snapshot]
2.6.32-431.20.3.el6.x86_64:RIP: 0010:[<ffffffffa039ae3f>]  [<ffffffffa039ae3f>] persistent_commit_exception+0x14f/0x160 [dm_snapshot]

Below is call backtrace :

crash> bt
PID: 16582  TASK: ffff8817fa140aa0  CPU: 5   COMMAND: "kcopyd"
 #0 [ffff880dbc92b9d0] machine_kexec at ffffffff8103b68b
 #1 [ffff880dbc92ba30] crash_kexec at ffffffff810c9852
 #2 [ffff880dbc92bb00] oops_end at ffffffff8152e090
 #3 [ffff880dbc92bb30] die at ffffffff81010fab
 #4 [ffff880dbc92bb60] do_trap at ffffffff8152d8f4
 #5 [ffff880dbc92bbc0] do_invalid_op at ffffffff8100cf95
 #6 [ffff880dbc92bc60] invalid_op at ffffffff8100bf9b
    [exception RIP: persistent_commit_exception+343]
    RIP: ffffffffa0477ff7  RSP: ffff880dbc92bd10  RFLAGS: 00010246
    RAX: 0000000000000000  RBX: ffff882d09c6a840  RCX: ffff882a36f4f628
    RDX: ffffffffa0475250  RSI: 0000000000000006  RDI: 00000000000251b2
    RBP: ffff880dbc92bd20   R8: 0000000000000000   R9: 0000000000000000
    R10: ffff881820346e80  R11: 0000000000000001  R12: ffffffffa0475180
    R13: ffff882940070670  R14: 0000000000000000  R15: ffff8828915aace0
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
 #7 [ffff880dbc92bd28] complete_exception at ffffffffa0475163 [dm_snapshot]
 #8 [ffff880dbc92bd38] copy_callback at ffffffffa0475204 [dm_snapshot]
 #9 [ffff880dbc92bd68] run_complete_job at ffffffffa000b668 [dm_mod]
#10 [ffff880dbc92bdb8] process_jobs at ffffffffa000b07b [dm_mod]
#11 [ffff880dbc92be18] do_work at ffffffffa000b146 [dm_mod]
#12 [ffff880dbc92be38] worker_thread at ffffffff81097fe0
#13 [ffff880dbc92bee8] kthread at ffffffff8109e66e
#14 [ffff880dbc92bf48] kernel_thread at ffffffff8100c20a