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    Subject[PATCH 1/6] ext2 balloc: fix _with_rsv freeze
    After several days of testing ext2 with reservations, it got caught inside
    ext2_try_to_allocate_with_rsv: alloc_new_reservation repeatedly succeeding
    on the window [12cff,12d0e], ext2_try_to_allocate repeatedly failing to
    find the free block guaranteed to be included (unless there's contention).

    Fix the range to find_next_usable_block's memscan: the scan from "here"
    (0xcfe) up to (but excluding) "maxblocks" (0xd0e) needs to scan 3 bytes
    not 2 (the relevant bytes of bitmap in this case being f7 df ff - none
    00, but the premature cutoff implying that the last was found 00).

    Is this a problem for mainline ext2? No, because the "size" in its memscan
    is always EXT2_BLOCKS_PER_GROUP(sb), which mkfs.ext2 requires to be a
    multiple of 8. Is this a problem for ext3 or ext4? No, because they have
    an additional extN_test_allocatable test which rescues them from the error.

    Signed-off-by: Hugh Dickins <>
    But the bigger question is, why does the my_rsv case come here to
    find_next_usable_block at all? Doesn't its 64-bit boundary limit, and its
    memscan, blithely ignore what the reservation prepared? It's messy too,
    the complement of the memscan being that "i < 7" loop over in
    ext2_try_to_allocate. I think this ought to be cleaned up,
    in ext2+reservations and ext3 and ext4.

    fs/ext2/balloc.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- 2.6.19-rc6-mm2/fs/ext2/balloc.c 2006-11-24 08:18:02.000000000 +0000
    +++ linux/fs/ext2/balloc.c 2006-11-27 19:28:41.000000000 +0000
    @@ -570,7 +570,7 @@ find_next_usable_block(int start, struct
    here = 0;

    p = ((char *)bh->b_data) + (here >> 3);
    - r = memscan(p, 0, (maxblocks - here + 7) >> 3);
    + r = memscan(p, 0, ((maxblocks + 7) >> 3) - (here >> 3));
    next = (r - ((char *)bh->b_data)) << 3;

    if (next < maxblocks && next >= here)
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      Last update: 2006-11-28 18:43    [W:0.024 / U:3.880 seconds]
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