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    SubjectPossible race between direct IO and JBD?

    While looking at a bug related to direct IO returns to EIO, after
    looking at the code, I found there is a window that
    try_to_free_buffers() from direct IO could race with JBD, which holds
    the reference to the data buffers before journal_commit_transaction()
    ensures the data buffers has reached to the disk.

    A little more detail: to prepare for direct IO, generic_file_direct_IO()
    calls invalidate_inode_pages2_range() to invalidate the pages in the
    cache before performaning direct IO. invalidate_inode_pages2_range()
    tries to free the buffers via try_to free_buffers(), but sometimes it
    can't, due to the buffers is possible still on some transaction's
    t_sync_datalist or t_locked_list waiting for
    journal_commit_transaction() to process it.

    Currently Direct IO simply returns EIO if try_to_free_buffers() finds
    the buffer is busy, as it has no clue that JBD is referencing it.

    Is this a known issue and expected behavior? Any thoughts?


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