On 08/01/2013 12:39 PM, Miklos Szeredi wrote:
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
Adding in the NFS list for broader review.
I thought that the issue was primarily in FUSE itself, not seen in practice in NFS?
Ric
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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