fs: Fix namespace related hangs

Nick converted the dentry->d_mounted counter to a flag, however with
namespaces, dentries can be mounted multiple times (and more
importantly unmounted multiple times).

If a namespace was created and then released, the unmount_tree would
remove the DCACHE_MOUNTED flag and that would make d_mountpoint fail,
causing the mounts to be lost.

This patch coverts it back to a counter, and adds some extra WARN_ONs
to make sure things are accounted properly.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: "Luis Claudio R. Goncalves" <lclaudio@uudg.org>
Cc: Nick Piggin <npiggin@suse.de>
LKML-Reference: <1272522942.1967.12.camel@work-vm>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

5 files changed, 10 insertions, 5 deletions

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index dc629eea0b91..60a7c6ce0a0d 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -296,7 +296,8 @@ struct dentry *autofs4_expire_direct(struct super_block *sb,
 		if (d_mountpoint(root)) {
 			ino->flags |= AUTOFS_INF_MOUNTPOINT;
 			spin_lock(&root->d_lock);
-			root->d_flags &= ~DCACHE_MOUNTED;
+			WARN_ON(root->d_mounted == 0);
+			root->d_mounted--;
 			spin_unlock(&root->d_lock);
 		}
 		ino->flags |= AUTOFS_INF_EXPIRING;
@@ -536,7 +537,7 @@ int autofs4_do_expire_multi(struct super_block *sb, struct vfsmount *mnt,
 		spin_lock(&sbi->fs_lock);
 		if (ino->flags & AUTOFS_INF_MOUNTPOINT) {
 			spin_lock(&sb->s_root->d_lock);
-			sb->s_root->d_flags |= DCACHE_MOUNTED;
+			sb->s_root->d_mounted++;
 			spin_unlock(&sb->s_root->d_lock);
 			ino->flags &= ~AUTOFS_INF_MOUNTPOINT;
 		}
diff --git a/fs/dcache.c b/fs/dcache.c
index c2a4d2ebe0e4..89b9d1f14871 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1187,6 +1187,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
 	dentry->d_sb = NULL;
 	dentry->d_op = NULL;
 	dentry->d_fsdata = NULL;
+	dentry->d_mounted = 0;
 	INIT_HLIST_NODE(&dentry->d_hash);
 	INIT_LIST_HEAD(&dentry->d_lru);
 	INIT_LIST_HEAD(&dentry->d_subdirs);
diff --git a/fs/libfs.c b/fs/libfs.c
index 48fe7c883d27..98d2717e9027 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -265,6 +265,7 @@ int get_sb_pseudo(struct file_system_type *fs_type, char *name,
 	d_instantiate(dentry, root);
 	s->s_root = dentry;
 	s->s_flags |= MS_ACTIVE;
+	WARN_ON(mnt->mnt_flags & MNT_MOUNTED);
 	mnt->mnt_flags |= MNT_MOUNTED;
 	simple_set_mnt(mnt, s);
 	return 0;
diff --git a/fs/namespace.c b/fs/namespace.c
index 6c115d86a157..64db957bb992 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -586,7 +586,8 @@ static void dentry_reset_mounted(struct vfsmount *mnt, struct dentry *dentry)
 {
 	if (!__lookup_mnt(mnt, dentry, 0)) {
 		spin_lock(&dentry->d_lock);
-		dentry->d_flags &= ~DCACHE_MOUNTED;
+		WARN_ON(dentry->d_mounted == 0);
+		dentry->d_mounted--;
 		spin_unlock(&dentry->d_lock);
 	}
 }
@@ -610,7 +611,7 @@ void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
 	child_mnt->mnt_parent = mntget(mnt);
 	spin_lock(&dentry->d_lock);
 	child_mnt->mnt_mountpoint = dget_dlock(dentry);
-	dentry->d_flags |= DCACHE_MOUNTED;
+	dentry->d_mounted++;
 	spin_unlock(&dentry->d_lock);
 }
 
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 39872ea86c6a..bc5a5ff141c8 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -99,6 +99,7 @@ struct dentry {
 	atomic_t d_count;
 	unsigned int d_flags;		/* protected by d_lock */
 	spinlock_t d_lock;		/* per dentry lock */
+	int d_mounted;
 	seqcount_t d_seq;		/* per dentry seqlock */
 	struct inode *d_inode;		/* Where the name belongs to - NULL is
 					 * negative */
@@ -364,7 +365,7 @@ extern void dput(struct dentry *);
 
 static inline int d_mountpoint(struct dentry *dentry)
 {
-	return dentry->d_flags & DCACHE_MOUNTED;
+	return dentry->d_mounted;
 }
 
 extern struct vfsmount *lookup_mnt(struct path *);