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    Subject[patch 26/39] ext4: Fix race between read_block_bitmap() and mark_diskspace_used()

    2.6.28-stable review patch. If anyone has any objections, please let us know.

    ------------------
    From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

    (cherry picked from commit e8134b27e351e813414da3b95aa8eac6d3908088)

    We need to make sure we update the block bitmap and clear
    EXT4_BG_BLOCK_UNINIT flag with sb_bgl_lock held, since
    ext4_read_block_bitmap() looks at EXT4_BG_BLOCK_UNINIT to decide
    whether to initialize the block bitmap each time it is called
    (introduced by commit c806e68f), and this can race with block
    allocations in ext4_mb_mark_diskspace_used().

    ext4_read_block_bitmap does:

    spin_lock(sb_bgl_lock(EXT4_SB(sb), block_group));
    if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
    ext4_init_block_bitmap(sb, bh, block_group, desc);
    Now on the block allocation side we do

    mb_set_bits(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group), bitmap_bh->b_data,
    ac->ac_b_ex.fe_start, ac->ac_b_ex.fe_len);
    ....
    spin_lock(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group));
    if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
    gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
    ie on allocation we update the bitmap then we take the sb_bgl_lock
    and clear the EXT4_BG_BLOCK_UNINIT flag. What can happen is a
    parallel ext4_read_block_bitmap can zero out the bitmap in between
    the above mb_set_bits and spin_lock(sb_bg_lock..)

    The race results in below user visible errors
    EXT4-fs error (device sdb1): ext4_mb_release_inode_pa: free 100, pa_free 105
    EXT4-fs error (device sdb1): mb_free_blocks: double-free of inode 0's block ..

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/ext4/mballoc.c | 15 ++++++++++-----
    1 file changed, 10 insertions(+), 5 deletions(-)
    --- a/fs/ext4/mballoc.c
    +++ b/fs/ext4/mballoc.c
    @@ -1070,7 +1070,10 @@ static void mb_clear_bits(spinlock_t *lo
    cur += 32;
    continue;
    }
    - mb_clear_bit_atomic(lock, cur, bm);
    + if (lock)
    + mb_clear_bit_atomic(lock, cur, bm);
    + else
    + mb_clear_bit(cur, bm);
    cur++;
    }
    }
    @@ -1088,7 +1091,10 @@ static void mb_set_bits(spinlock_t *lock
    cur += 32;
    continue;
    }
    - mb_set_bit_atomic(lock, cur, bm);
    + if (lock)
    + mb_set_bit_atomic(lock, cur, bm);
    + else
    + mb_set_bit(cur, bm);
    cur++;
    }
    }
    @@ -3033,10 +3039,9 @@ ext4_mb_mark_diskspace_used(struct ext4_
    }
    }
    #endif
    - mb_set_bits(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group), bitmap_bh->b_data,
    - ac->ac_b_ex.fe_start, ac->ac_b_ex.fe_len);
    -
    spin_lock(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group));
    + mb_set_bits(NULL, bitmap_bh->b_data,
    + ac->ac_b_ex.fe_start, ac->ac_b_ex.fe_len);
    if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
    gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
    gdp->bg_free_blocks_count =


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