• Bob Peterson's avatar
    GFS2: gfs2_free_extlen can return an extent that is too long · dc8fbb03
    Bob Peterson authored
    Function gfs2_free_extlen calculates the length of an extent of
    free blocks that may be reserved. The end pointer was calculated as
    end = start + bh->b_size but b_size is incorrect because the
    bitmap usually stops prior to the end of the buffer data on
    the last bitmap.
    
    What this means is that when you do a write, you can reserve a
    chunk of blocks that runs off the end of the last bitmap. For
    example, I've got a file system where there is only one bitmap
    for each rgrp, so ri_length==1. I saw cases in which iozone
    tried to do a big write, grabbed a large block reservation,
    chose rgrp 5464152, which has ri_data0 5464153 and ri_data 8188.
    So 5464153 + 8188 = 5472341 which is the end of the rgrp.
    
    When it grabbed a reservation it got back: 5470936, length 7229.
    But 5470936 + 7229 = 5478165. So the reservation starts inside
    the rgrp but runs 5824 blocks past the end of the bitmap.
    
    This patch fixes the calculation so it won't exceed the last
    bitmap. It also adds a BUG_ON to guard against overflows in the
    future.
    Signed-off-by: default avatarBob Peterson <rpeterso@redhat.com>
    dc8fbb03
rgrp.c 69.2 KB