Hi,
      Thanks for that SysRq tip. Now I am able to get some logs.

 From OOPS message, it showed an assertion failure on
     J_ASSERT_JH(jh, jh->b_transaction == 
journal->j_committing_transaction);

In my code, I've modified journal_commit_transaction such that it 
collects all buffer_head in a linked list, with their corresponding
buffer numbers in other list.
      I collect all buffers (data + metadata ) and push them all 
simultaneously and pass list of block numbers through a special ioctl call.

The problem that I see in my code is that all buffers are handled in 
same way as all data buffers in original code. ie metadata buffers are
getting unfiled instead of refiling.

I am attaching my patch. Please can you see and check if that indeed is 
problem here?

Also what can be possible solution to it? separation of buffers in 2 
list (data, metadata) and handling them separately?

(Being a kernel noob, my coding does not conform to any standard. So 
please point out any blunders I've committed in my patch)

Thank You
Niraj