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    SubjectRe: lock i_mutex for fallocate?
    On Wed, Aug 31, 2011 at 05:33:25PM -0700, Allison Henderson wrote:
    > Hi All,
    > In ext4 punch hole, we realized that the punch hole operation needs
    > to be done under i_mutex just like truncate. i_mutex for truncate
    > is held in the vfs layer, so we dont need to lock it at the file
    > system layer, but vfs does not lock i_mutex for fallocate. We can
    > lock i_mutex for fallocate at the fs layer, but question was raised
    > then: should i_mutex for fallocate be held in the vfs layer instead?


    > I do not know if other file systems need i_mutex to be locked for
    > fallocate,

    For one, XFS does not require i_mutex to be held for any extent
    manipulation of any kind (allocation, truncation, hole punch,
    unwritten extent conversion, etc).

    Hence the current structure of having the filesystem take i_mutex if
    it needs it to protect allocations against races is appropriate.


    Dave Chinner

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