On Fri, Aug 29, 2014 at 05:57:22PM +0800, Xue jiufei wrote:

The patch trys to solve one deadlock problem caused by cluster
fs, like ocfs2. And the problem may happen at least in the below
situations:
1)Receiving a connect message from other nodes, node queues a
work_struct o2net_listen_work.
2)o2net_wq processes this work and calls sock_alloc() to allocate
memory for a new socket.
3)It would do direct memory reclaim when available memory is not
enough and trigger the inode cleanup. That inode being cleaned up
is happened to be ocfs2 inode, so call evict()->ocfs2_evict_inode()
->ocfs2_drop_lock()->dlmunlock()->o2net_send_message_vec(),
and wait for the unlock response from master.
4)tcp layer received the response, call o2net_data_ready() and
queue sc_rx_work, waiting o2net_wq to process this work.
5)o2net_wq is a single thread workqueue, it process the work one by
one. Right now it is still doing o2net_listen_work and cannot handle
sc_rx_work. so we deadlock.

It is impossible to set GFP_NOFS for memory allocation in sock_alloc().
So we use PF_FSTRANS to avoid the task reentering filesystem when
available memory is not enough.

Signed-off-by: joyce.xue <redacted>

For the second time: use memalloc_noio_save/memalloc_noio_restore.
And please put a great big comment in the code explaining why you
need to do this special thing with memory reclaim flags.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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