• Mike Snitzer's avatar
    block: remove management of bi_remaining when restoring original bi_end_io · 326e1dbb
    Mike Snitzer authored
    Commit c4cf5261 ("bio: skip atomic inc/dec of ->bi_remaining for
    non-chains") regressed all existing callers that followed this pattern:
     1) saving a bio's original bi_end_io
     2) wiring up an intermediate bi_end_io
     3) restoring the original bi_end_io from intermediate bi_end_io
     4) calling bio_endio() to execute the restored original bi_end_io
    
    The regression was due to BIO_CHAIN only ever getting set if
    bio_inc_remaining() is called.  For the above pattern it isn't set until
    step 3 above (step 2 would've needed to establish BIO_CHAIN).  As such
    the first bio_endio(), in step 2 above, never decremented __bi_remaining
    before calling the intermediate bi_end_io -- leaving __bi_remaining with
    the value 1 instead of 0.  When bio_inc_remaining() occurred during step
    3 it brought it to a value of 2.  When the second bio_endio() was
    called, in step 4 above, it should've called the original bi_end_io but
    it didn't because there was an extra reference that wasn't dropped (due
    to atomic operations being optimized away since BIO_CHAIN wasn't set
    upfront).
    
    Fix this issue by removing the __bi_remaining management complexity for
    all callers that use the above pattern -- bio_chain() is the only
    interface that _needs_ to be concerned with __bi_remaining.  For the
    above pattern callers just expect the bi_end_io they set to get called!
    Remove bio_endio_nodec() and also remove all bio_inc_remaining() calls
    that aren't associated with the bio_chain() interface.
    
    Also, the bio_inc_remaining() interface has been moved local to bio.c.
    
    Fixes: c4cf5261
    
     ("bio: skip atomic inc/dec of ->bi_remaining for non-chains")
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
    326e1dbb
dm-thin.c 102 KB