• Chen, Kenneth W's avatar
    [PATCH] direct-io: bug fix in dio handling write error · 174e27c6
    Chen, Kenneth W authored
    There is a bug in direct-io on propagating write error up to the higher I/O
    layer.  When performing an async ODIRECT write to a block device, if a
    device error occurred (like media error or disk is pulled), the error code
    is only propagated from device driver to the DIO layer.  The error code
    stops at finished_one_bio().  The aysnc write, however, is supposedly have
    a corresponding AIO event with appropriate return code (in this case -EIO).
     Application which waits on the async write event, will hang forever since
    such AIO event is lost forever (if such app did not use the timeout option
    in io_getevents call.  Regardless, an AIO event is lost).
    The discovery of above bug leads to another discovery of potential race
    window with dio->result.  The fundamental problem is that dio->result is
    overloaded with dual use: an indicator of fall back path for partial dio
    write, and an error indicator used in the I/O completion path.  In the
    event of device error, the setting of -EIO to dio->result clashes with
    value used to track partial write that activates the fall back path.
    It was also pointed out that it is impossible to use dio->result to track
    partial write and at the same time to track error returned from device
    driver.  Because direct_io_work can only determines whether it is a partial
    write at the end of io submission and in mid stream of those io submission,
    a return code could be coming back from the driver.  Thus messing up all
    the subsequent logic.
    Proposed fix is to separating out error code returned by the IO completion
    path from partial IO submit tracking.  A new variable is added to dio
    structure specifically to track io error returned in the completion path.
    Signed-off-by: default avatarKen Chen <kenneth.w.chen@intel.com>
    Acked-by: default avatarZach Brown <zach.brown@oracle.com>
    Acked-by: default avatarSuparna Bhattacharya <suparna@in.ibm.com>
    Cc: Badari Pulavarty <pbadari@us.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
direct-io.c 35 KB