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    ocfs2: fix a deadlock while o2net_wq doing direct memory reclaim · b246d3d1
    Xue jiufei 提交于
    Fix a deadlock problem caused by direct memory reclaim in o2net_wq.  The
    situation is as follows:
    
    1) Receive a connect message from another node, node queues a
       work_struct o2net_listen_work.
    
    2) o2net_wq processes this work and call the following functions:
    
    o2net_wq
    -> o2net_accept_one
      -> sock_create_lite
        -> sock_alloc()
          -> kmem_cache_alloc with GFP_KERNEL
            -> ____cache_alloc_node
              ->__alloc_pages_nodemask
                -> do_try_to_free_pages
                  -> shrink_slab
                    -> evict
                      -> ocfs2_evict_inode
                        -> ocfs2_drop_lock
                          -> dlmunlock
                            -> o2net_send_message_vec
    
       then o2net_wq wait for the unlock reply from master.
    
    3) tcp layer received the reply, call o2net_data_ready() and queue
       sc_rx_work, waiting o2net_wq to process this work.
    
    4) 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.
    
    Junxiao Bi's patch "mm: clear __GFP_FS when PF_MEMALLOC_NOIO is set"
    (http://ozlabs.org/~akpm/mmots/broken-out/mm-clear-__gfp_fs-when-pf_memalloc_noio-is-set.patch)
    clears __GFP_FS in memalloc_noio_flags() besides __GFP_IO.  We use
    memalloc_noio_save() to set process flag PF_MEMALLOC_NOIO so that all
    allocations done by this process are done as if GFP_NOIO was specified.
    We are not reentering filesystem while doing memory reclaim.
    Signed-off-by: Njoyce.xue <xuejiufei@huawei.com>
    Cc: Junxiao Bi <junxiao.bi@oracle.com>
    Cc: Joel Becker <jlbec@evilplan.org>
    Cc: Mark Fasheh <mfasheh@suse.com>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    b246d3d1
tcp.c 60.4 KB