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    Subject[PATCH 4.9 196/240] NFS: Deal correctly with attribute generation counter overflow
    Date
    From: Trond Myklebust <trond.myklebust@hammerspace.com>

    [ Upstream commit 9fdbfad1777cb4638f489eeb62d85432010c0031 ]

    We need to use unsigned long subtraction and then convert to signed in
    order to deal correcly with C overflow rules.

    Fixes: f5062003465c ("NFS: Set an attribute barrier on all updates")
    Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/nfs/inode.c | 8 ++++----
    1 file changed, 4 insertions(+), 4 deletions(-)

    diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
    index 6c0035761d17..7a94f5a5f8c8 100644
    --- a/fs/nfs/inode.c
    +++ b/fs/nfs/inode.c
    @@ -1469,10 +1469,10 @@ EXPORT_SYMBOL_GPL(_nfs_display_fhandle);
    */
    static int nfs_inode_attrs_need_update(const struct inode *inode, const struct nfs_fattr *fattr)
    {
    - const struct nfs_inode *nfsi = NFS_I(inode);
    + unsigned long attr_gencount = NFS_I(inode)->attr_gencount;

    - return ((long)fattr->gencount - (long)nfsi->attr_gencount) > 0 ||
    - ((long)nfsi->attr_gencount - (long)nfs_read_attr_generation_counter() > 0);
    + return (long)(fattr->gencount - attr_gencount) > 0 ||
    + (long)(attr_gencount - nfs_read_attr_generation_counter()) > 0;
    }

    static int nfs_refresh_inode_locked(struct inode *inode, struct nfs_fattr *fattr)
    @@ -1882,7 +1882,7 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
    nfsi->attrtimeo_timestamp = now;
    }
    /* Set the barrier to be more recent than this fattr */
    - if ((long)fattr->gencount - (long)nfsi->attr_gencount > 0)
    + if ((long)(fattr->gencount - nfsi->attr_gencount) > 0)
    nfsi->attr_gencount = fattr->gencount;
    }

    --
    2.30.2


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