Re: [PATCH 12/22] elevate write count files are open()ed

Andrew Morton
2007-02-13T05:13:32Z

On Fri, 09 Feb 2007 14:53:37 -0800 Dave Hansen <hansendc@us.ibm.com> wrote:

> diff -puN fs/file_table.c~14-24-tricky-elevate-write-count-files-are-open-ed fs/file_table.c
> --- lxc/fs/file_table.c~14-24-tricky-elevate-write-count-files-are-open-ed 2007-02-09 14:26:54.000000000 -0800
> +++ lxc-dave/fs/file_table.c 2007-02-09 14:26:54.000000000 -0800
> @@ -209,8 +209,11 @@ void fastcall __fput(struct file *file)
> if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
> cdev_put(inode->i_cdev);
> fops_put(file->f_op);
> - if (file->f_mode & FMODE_WRITE)
> + if (file->f_mode & FMODE_WRITE) {
> put_write_access(inode);
> + if(!special_file(inode->i_mode))
> + mnt_drop_write(mnt);
> + }
> put_pid(file->f_owner.pid);
> put_user_ns(file->f_owner.user_ns);
> file_kill(file);
> diff -puN fs/namei.c~14-24-tricky-elevate-write-count-files-are-open-ed fs/namei.c
> --- lxc/fs/namei.c~14-24-tricky-elevate-write-count-files-are-open-ed 2007-02-09 14:26:54.000000000 -0800
> +++ lxc-dave/fs/namei.c 2007-02-09 14:26:54.000000000 -0800
> @@ -1548,8 +1548,17 @@ int may_open(struct nameidata *nd, int a
> return -EACCES;
>
> flag &= ~O_TRUNC;
> - } else if (IS_RDONLY(inode) && (flag & FMODE_WRITE))
> - return -EROFS;
> + } else if (flag & FMODE_WRITE) {
> + /*
> + * effectively: !special_file()
> + * balanced by __fput()
> + */
> + error = mnt_want_write(nd->mnt);
> + if (error)
> + return error;
> + if (IS_RDONLY(inode))
> + return -EROFS;
> + }

yipes. A new mount-wide spin_lock/unlock for each for-writing open() and close().
Can we have a microbenchmark on this please?

Are you sure that fget_light() and fput_light() don't accidentally bypass this
new logic?