On Wed, 2 Dec 2009, Jeff Layton wrote: > In the case of a bind mounted file, the path walking code will assume > that the cached dentry that was bind mounted is valid. This is a problem > problem for NFSv4 in a way that's similar to LAST_BIND symlinks. > > Fix this by revalidating the dentry if FS_FOLLOW_DOT is set and > __follow_mount returns true. > > Note that in the non-open codepath, we cannot return an error to the > lookup if the revalidation fails. Doing so will leave a bind mount in > a state such that we can't unmount it. In that case we'll just have to > settle for d_invalidating it (which should mostly turn out to be a > d_drop in this case) and returning success. The only worry I have is that this adds an extra branch in a very hot codepath (do_lookup). An error can't be returned, as you note, and for bind mounted directories d_invalidate() will not succeed: the directory is busy, it's referenced by the mount. So basically the only thing this does is working around the NFSv4 issue. But Trond has a proper solution to that, and a temporary solution could be added to do_filp_open() rather than burdening do_lookup() with it, no? Thanks, Miklos > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > --- > fs/namei.c | 11 ++++++++++- > 1 files changed, 10 insertions(+), 1 deletions(-) > > diff --git a/fs/namei.c b/fs/namei.c > index 339789e..0d55b6f 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -851,7 +851,13 @@ static int do_lookup(struct nameidata *nd, struct qstr *name, > done: > path->mnt = mnt; > path->dentry = dentry; > - __follow_mount(path); > + > + /* > + * cannot return the error returned by force_reval_path as that can > + * make it impossible to unmount a bind mounted dentry if it's stale. > + */ > + if (__follow_mount(path)) > + force_reval_path(path, nd); > return 0; > > need_lookup: > @@ -1840,6 +1846,9 @@ do_last: > error = -ELOOP; > if (flag & O_NOFOLLOW) > goto exit_dput; > + error = force_reval_path(&path, &nd); > + if (error) > + goto exit_dput; > } > > error = -ENOENT; > -- > 1.5.5.6 > > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
