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    [XFS] get_bulkall() could return incorrect inode state · 859d7182
    Vlad Apostolov 提交于
    In the following scenario xfs_bulkstat() returns incorrect stale inode
    state:
    
    1. File_A is created and its inode synced to disk. 2. File_A is unlinked
    and doesn't exist anymore. 3. Filesystem sync is invoked. 4. File_B is
    created. File_B happens to reclaim File_A's inode. 5. xfs_bulkstat() is
    called and detects File_B but reports the
    
    incorrect File_A inode state.
    
    Explanation for the incorrect inode state is that inodes are not
    immediately synced on file create for performance reasons. This leaves the
    on-disk inode buffer uninitialized (or with old state from a previous
    generation inode) and this is what xfs_bulkstat() would report.
    
    The patch marks the on-disk inode buffer "dirty" on unlink. When the inode
    is reclaimed (by a new file create), xfs_bulkstat() would filter this
    inode by the "dirty" mark. Once the inode is flushed to disk, the on-disk
    buffer "dirty" mark is automatically removed and a following
    xfs_bulkstat() would return the correct inode state.
    
    Marking the on-disk inode buffer "dirty" on unlink is achieved by setting
    the on-disk di_nlink field to 0. Note that the in-core di_nlink has
    already been set to 0 and a corresponding transaction logged by
    xfs_droplink(). This is an exception from the rule that any on-disk inode
    buffer changes has to be followed by a disk write (inode flush).
    Synchronizing the in-core to on-disk di_nlink values in advance (before
    the actual inode flush to disk) should be fine in this case because the
    inode is already unlinked and it would never change its di_nlink again for
    this inode generation.
    
    SGI-PV: 970842
    SGI-Modid: xfs-linux-melb:xfs-kern:29757a
    Signed-off-by: NVlad Apostolov <vapo@sgi.com>
    Signed-off-by: NAlex Elder <aelder@sgi.com>
    Signed-off-by: NDavid Chinner <dgc@sgi.com>
    Signed-off-by: NChristoph Hellwig <hch@infradead.org>
    Signed-off-by: NMark Goodwin <markgw@sgi.com>
    Signed-off-by: NTim Shimmin <tes@sgi.com>
    859d7182
xfs_inode.c 138.8 KB