• Tejun Heo's avatar
    [BLOCK] drop unnecessary bvec rewinding from flush_dry_bio_endio · f4b09303
    Tejun Heo authored
    Barrier bios are completed twice - once after the barrier write itself
    is done and again after the whole sequence is complete.
    flush_dry_bio_endio() is for the first completion.  It doesn't really
    complete the bio.  It rewinds bvec and resets bio so that it can be
    completed again when the whole barrier sequence is complete.
    
    The bvec rewinding code has the following problems.
    
    1. The rewinding code is wrong because filesystems may pass bvec with
       non zero bv_offset.
    
    2. The block layer doesn't guarantee anything about the state of
       bvec array on request completion.  bv_offset and len are updated
       iff __end_that_request_first() completes the bvec partially.
    
    Because of #2, #1 doesn't really matter (nobody cares whether bvec is
    re-wound correctly or not) but then again by not doing unwinding at
    all, we'll always give back the same bvec to the caller as full bvec
    completion doesn't alter bvecs and the final completion is always full
    completion.
    
    Drop unnecessary rewinding code.
    
    This is spotted by Neil Brown.
    Signed-off-by: default avatarTejun Heo <htejun@gmail.com>
    Cc: Neil Brown <neilb@suse.de>
    Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
    f4b09303
ll_rw_blk.c 105 KB