On Tue, 5 Nov 2013 13:39:59 +1100 NeilBrown <[email protected]> wrote: > On Mon, 4 Nov 2013 20:16:26 -0500 Jeff Layton <[email protected]> wrote: > > > We had a couple of reports of people that are mounting NFS filesystems, > > and then bind mounting certain local files onto dentries in that nfs > > mount (sort of like a poor-man's unionmount). > > > > This all works well until the dentry serving as the mountpoint fails > > d_revalidate. The dentry will end up being invalidated which makes the > > bind mount unreachable via pathwalk. > > > > It doesn't make much sense to me to allow dentries to serve as > > mountpoints to end up invalidated, so there's no real point in > > attempting to d_revalidate them at all. > > > > Reported-by: Patrick McLean <[email protected]> > > Reported-by: Guang Cheng Li <[email protected]> > > Signed-off-by: Jeff Layton <[email protected]> > > --- > > fs/namei.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/fs/namei.c b/fs/namei.c > > index caa2805..5b10ad0 100644 > > --- a/fs/namei.c > > +++ b/fs/namei.c > > @@ -585,6 +585,9 @@ drop_root_mnt: > > > > static inline int d_revalidate(struct dentry *dentry, unsigned int flags) > > { > > + /* dentries that serve as mountpoints are always considered valid */ > > + if (d_mountpoint(dentry)) > > + return 1; > > return dentry->d_op->d_revalidate(dentry, flags); > > } > > > > Makes sense to me. But what about the parent or grandparent of the mountpoint? > > Presumably we don't want to invalidate them either, and I don't think > d_mountpoint() returns true for those, does it? > > NeilBrown
Good point... I think we're probably saved there (at least on NFS) by the check_submounts_and_drop() call in nfs_lookup_revalidate. Hmmm, that said...I did do most of this testing on a slightly older kernel that doesn't have that call, and I can't reproduce this problem on a 3.12-ish kernel. I think this is probably already fixed by Miklos' patches that added that. Sorry for the noise! -- Jeff Layton <[email protected]>
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