• Xiaoguang Wang's avatar
    jbd2: fix deadlock while checkpoint thread waits commit thread to finish · 53cf9784
    Xiaoguang Wang authored
    This issue was found when I tried to put checkpoint work in a separate thread,
    the deadlock below happened:
             Thread1                                |   Thread2
    __jbd2_log_wait_for_space                       |
    jbd2_log_do_checkpoint (hold j_checkpoint_mutex)|
      if (jh->b_transaction != NULL)                |
        ...                                         |
        jbd2_log_start_commit(journal, tid);        |jbd2_update_log_tail
                                                    |  will lock j_checkpoint_mutex,
                                                    |  but will be blocked here.
                                                    |
        jbd2_log_wait_commit(journal, tid);         |
        wait_event(journal->j_wait_done_commit,     |
         !tid_gt(tid, journal->j_commit_sequence)); |
         ...                                        |wake_up(j_wait_done_commit)
      }                                             |
    
    then deadlock occurs, Thread1 will never be waken up.
    
    To fix this issue, drop j_checkpoint_mutex in jbd2_log_do_checkpoint()
    when we are going to wait for transaction commit.
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
    Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
    53cf9784
journal.c 75.7 KB