On Tue, Jul 30, 2013 at 03:30:45PM -0400, Ric Wheeler wrote:
> On 07/30/2013 12:16 PM, Miklos Szeredi wrote:
> >>> fs/fuse/dir.c | 4 ++++
> >>> 1 file changed, 4 insertions(+)
> >>>
> >>>diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> >>>index a1d9047..83c217e 100644
> >>>--- a/fs/fuse/dir.c
> >>>+++ b/fs/fuse/dir.c
> >>>@@ -226,6 +226,10 @@ static int fuse_dentry_revalidate(struct dentry
> >>>*entry, unsigned int flags)
> >>> if (!err) {
> >>> struct fuse_inode *fi = get_fuse_inode(inode);
> >>> if (outarg.nodeid != get_node_id(inode)) {
> >>>+ if (!have_submounts(entry)) {
> >>>+ shrink_dcache_parent(entry);
> >>>+ d_drop(entry);
> >>>+ }
> >Doing d_drop() on a subtree really has problems. Take this example:
> >
> >cd /mnt/foo/bar
> >mkdir my-mount-point
> >[->d_revalidate() drops "/mnt/foo"]
> >mount whatever on ./my-mount-point
> >cd /
> >
> >At this point that mount is not accessible in any way. The only way
> >to umount it is to lazy umount the parent mount. If the parent mount
> >was root, then that's not a practical thing to do.
> >
> >AFAICS nothing prevents this from happening on NFS and root privs are
> >not required (e.g. mounting a fuse fs on an NFS home dir).
> >
Here's a patch that tries to address the mount issue in NFS (and in FUSE in the
future). I haven't yet tested it, just interested in whether the concept looks
OK or not.
Not sure if the ENOENT is the best error. Also I have a little fear that this
will cause a regression in some weird setup. Possibly we should use a new
dentry flag for unhashing the directory dentry specifically to invalidate it.
Thanks,
Miklos
diff --git a/fs/dcache.c b/fs/dcache.c
index 87bdb53..5c51217 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1103,6 +1103,34 @@ rename_retry:
}
EXPORT_SYMBOL(have_submounts);
+static bool __has_unlinked_ancestor(struct dentry *dentry)
+{
+ struct dentry *this;
+
+ for (this = dentry; !IS_ROOT(this); this = this->d_parent) {
+ if (d_unhashed(this))
+ return true;
+ }
+ return false;
+}
+
+/*
+ * Called by mount code to check if the mountpoint is reachable (e.g. NFS can
+ * unhash a directory dentry and then the complete subtree can become
+ * unreachable).
+ */
+bool has_unlinked_ancestor(struct dentry *dentry)
+{
+ bool found;
+
+ /* Need exclusion wrt. have_submounts() */
+ write_seqlock(&rename_lock);
+ found = __has_unlinked_ancestor(dentry);
+ write_sequnlock(&rename_lock);
+
+ return found;
+}
+
/*
* Search the dentry child list of the specified parent,
* and move any unused dentries to the end of the unused
diff --git a/fs/internal.h b/fs/internal.h
index 7c5f01c..d232355 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -126,6 +126,7 @@ extern int invalidate_inodes(struct super_block *, bool);
* dcache.c
*/
extern struct dentry *__d_alloc(struct super_block *, const struct qstr *);
+extern bool has_unlinked_ancestor(struct dentry *dentry);
/*
* read_write.c
diff --git a/fs/namespace.c b/fs/namespace.c
index 7b1ca9b..bb92a9c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -634,6 +634,15 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry)
}
dentry->d_flags |= DCACHE_MOUNTED;
spin_unlock(&dentry->d_lock);
+
+ if (has_unlinked_ancestor(dentry)) {
+ spin_lock(&dentry->d_lock);
+ dentry->d_flags &= ~DCACHE_MOUNTED;
+ spin_unlock(&dentry->d_lock);
+ kfree(mp);
+ return ERR_PTR(-ENOENT);
+ }
+
mp->m_dentry = dentry;
mp->m_count = 1;
list_add(&mp->m_hash, chain);
--
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