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    Subject[RFC][PATCH 25/27] elevate writer count for custom 'struct file'
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    Some filesystems forego the vfs and may_open() and create their
    own 'struct file's. Any of these users which set the write flag
    on the file will cause an extra mnt_drop_write() on __fput(),
    thus dropping the reference count too low.

    These users tend to have artifical in-kernel vfsmounts which
    aren't really exposed to userspace and can't be remounted, but
    this patch is included for completeness and so that the warnings
    don't trip over these cases.

    Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
    ---

    lxc-dave/fs/hugetlbfs/inode.c | 2 ++
    lxc-dave/mm/shmem.c | 2 ++
    lxc-dave/mm/tiny-shmem.c | 2 ++
    lxc-dave/net/socket.c | 3 +++
    4 files changed, 9 insertions(+)

    diff -puN fs/hugetlbfs/inode.c~C-elevate-writer-count-for-custom-struct_file fs/hugetlbfs/inode.c
    --- lxc/fs/hugetlbfs/inode.c~C-elevate-writer-count-for-custom-struct_file 2006-07-12 11:09:09.000000000 -0700
    +++ lxc-dave/fs/hugetlbfs/inode.c 2006-07-12 11:09:43.000000000 -0700
    @@ -787,6 +787,8 @@ struct file *hugetlb_zero_setup(size_t s
    file->f_mapping = inode->i_mapping;
    file->f_op = &hugetlbfs_file_operations;
    file->f_mode = FMODE_WRITE | FMODE_READ;
    + error = mnt_want_write(hugetlbfs_vfsmount);
    + WARN_ON(error);
    return file;

    out_inode:
    diff -puN mm/shmem.c~C-elevate-writer-count-for-custom-struct_file mm/shmem.c
    --- lxc/mm/shmem.c~C-elevate-writer-count-for-custom-struct_file 2006-07-12 11:09:19.000000000 -0700
    +++ lxc-dave/mm/shmem.c 2006-07-12 11:09:43.000000000 -0700
    @@ -2322,6 +2322,8 @@ struct file *shmem_file_setup(char *name
    file->f_mapping = inode->i_mapping;
    file->f_op = &shmem_file_operations;
    file->f_mode = FMODE_WRITE | FMODE_READ;
    + error = mnt_want_write(shm_mnt);
    + WARN_ON(error);
    return file;

    close_file:
    diff -puN mm/tiny-shmem.c~C-elevate-writer-count-for-custom-struct_file mm/tiny-shmem.c
    --- lxc/mm/tiny-shmem.c~C-elevate-writer-count-for-custom-struct_file 2006-07-12 11:09:09.000000000 -0700
    +++ lxc-dave/mm/tiny-shmem.c 2006-07-12 11:09:43.000000000 -0700
    @@ -84,6 +84,8 @@ struct file *shmem_file_setup(char *name
    file->f_mapping = inode->i_mapping;
    file->f_op = &ramfs_file_operations;
    file->f_mode = FMODE_WRITE | FMODE_READ;
    + error = mnt_want_write(shm_mnt);
    + WARN_ON(error);

    /* notify everyone as to the change of file size */
    error = do_truncate(dentry, size, 0, file);
    diff -puN net/socket.c~C-elevate-writer-count-for-custom-struct_file net/socket.c
    --- lxc/net/socket.c~C-elevate-writer-count-for-custom-struct_file 2006-07-12 11:09:09.000000000 -0700
    +++ lxc-dave/net/socket.c 2006-07-12 11:09:43.000000000 -0700
    @@ -389,6 +389,7 @@ static int sock_attach_fd(struct socket
    {
    struct qstr this;
    char name[32];
    + int error;

    this.len = sprintf(name, "[%lu]", SOCK_INODE(sock)->i_ino);
    this.name = name;
    @@ -409,6 +410,8 @@ static int sock_attach_fd(struct socket
    file->f_flags = O_RDWR;
    file->f_pos = 0;
    file->private_data = sock;
    + error = mnt_want_write(sock_mnt);
    + WARN_ON(error);

    return 0;
    }
    _
    -
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