Re: [PATCH 09/30] r/o bind mounts: drop write during emergency remount

Miklos Szeredi
2008-02-18T16:29:28Z

> The emergency remount code forcibly removes FMODE_WRITE from
> filps. The r/o bind mount code notices that this was done
> without a proper mnt_drop_write() and properly gives a
> warning.
>
> This patch does a mnt_drop_write() to keep everything
> balanced.
>
> Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
> Signed-off-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
> ---
>
> linux-2.6.git-dave/fs/super.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff -puN fs/super.c~robind-sysrq-fix fs/super.c
> --- linux-2.6.git/fs/super.c~robind-sysrq-fix 2008-02-15 13:25:46.000000000 -0800
> +++ linux-2.6.git-dave/fs/super.c 2008-02-15 13:25:46.000000000 -0800
> @@ -37,6 +37,7 @@
> #include <linux/idr.h>
> #include <linux/kobject.h>
> #include <linux/mutex.h>
> +#include <linux/file.h>
> #include <asm/uaccess.h>
>
>
> @@ -567,10 +568,25 @@ static void mark_files_ro(struct super_b
> {
> struct file *f;
>
> +retry:
> file_list_lock();
> list_for_each_entry(f, &sb->s_files, f_u.fu_list) {
> - if (S_ISREG(f->f_path.dentry->d_inode->i_mode) && file_count(f))
> - f->f_mode &= ~FMODE_WRITE;
> + struct vfsmount *mnt;
> + if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
> + continue;
> + if (!file_count(f))
> + continue;
> + if (!(f->f_mode & FMODE_WRITE))
> + continue;
> + f->f_mode &= ~FMODE_WRITE;
> + mnt = f->f_path.mnt;

AFAICS an mntget() is needed here to make sure mnt doesn't go away
after releasing file_list_lock.

Miklos

> + file_list_unlock();
> + /*
> + * This can sleep, so we can't hold
> + * the file_list_lock() spinlock.
> + */
> + mnt_drop_write(mnt);
> + goto retry;
> }
> file_list_unlock();
> }
> _
>