spufs: fix gang directory lifetimes

prior to "[POWERPC] spufs: Fix gang destroy leaks" we used to have
a problem with gang lifetimes - creation of a gang returns opened
gang directory, which normally gets removed when that gets closed,
but if somebody has created a context belonging to that gang and
kept it alive until the gang got closed, removal failed and we
ended up with a leak.

Unfortunately, it had been fixed the wrong way.  Dentry of gang
directory was no longer pinned, and rmdir on close was gone.
One problem was that failure of open kept calling simple_rmdir()
as cleanup, which meant an unbalanced dput().  Another bug was
in the success case - gang creation incremented link count on
root directory, but that was no longer undone when gang got
destroyed.

Fix consists of
	* reverting the commit in question
	* adding a counter to gang, protected by ->i_rwsem
of gang directory inode.
	* having it set to 1 at creation time, dropped
in both spufs_dir_close() and spufs_gang_close() and bumped
in spufs_create_context(), provided that it's not 0.
	* using simple_recursive_removal() to take the gang
directory out when counter reaches zero.

Fixes: 877907d "[POWERPC] spufs: Fix gang destroy leaks"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

arch/powerpc/platforms/cell/spufs/gang.c

@@ -25,6 +25,7 @@ struct spu_gang *alloc_spu_gang(void)
 	mutex_init(&gang->aff_mutex);
 	INIT_LIST_HEAD(&gang->list);
 	INIT_LIST_HEAD(&gang->aff_list_head);
+	gang->alive = 1;
 
 out:
 	return gang;

arch/powerpc/platforms/cell/spufs/inode.c

@@ -201,6 +201,23 @@ static int spufs_fill_dir(struct dentry *dir,
 	return 0;
 }
 
+static void unuse_gang(struct dentry *dir)
+{
+	struct inode *inode = dir->d_inode;
+	struct spu_gang *gang = SPUFS_I(inode)->i_gang;
+
+	if (gang) {
+		bool dead;
+
+		inode_lock(inode); // exclusion with spufs_create_context()
+		dead = !--gang->alive;
+		inode_unlock(inode);
+
+		if (dead)
+			simple_recursive_removal(dir, NULL);
+	}
+}
+
 static int spufs_dir_close(struct inode *inode, struct file *file)
 {
 	struct inode *parent;
@@ -215,6 +232,7 @@ static int spufs_dir_close(struct inode *inode, struct file *file)
 	inode_unlock(parent);
 	WARN_ON(ret);
 
+	unuse_gang(dir->d_parent);
 	return dcache_dir_close(inode, file);
 }
 
@@ -407,7 +425,7 @@ spufs_create_context(struct inode *inode, struct dentry *dentry,
 {
 	int ret;
 	int affinity;
-	struct spu_gang *gang;
+	struct spu_gang *gang = SPUFS_I(inode)->i_gang;
 	struct spu_context *neighbor;
 	struct path path = {.mnt = mnt, .dentry = dentry};
 
@@ -422,11 +440,15 @@ spufs_create_context(struct inode *inode, struct dentry *dentry,
 	if ((flags & SPU_CREATE_ISOLATE) && !isolated_loader)
 		return -ENODEV;
 
-	gang = NULL;
+	if (gang) {
+		if (!gang->alive)
+			return -ENOENT;
+		gang->alive++;
+	}
+
 	neighbor = NULL;
 	affinity = flags & (SPU_CREATE_AFFINITY_MEM | SPU_CREATE_AFFINITY_SPU);
 	if (affinity) {
-		gang = SPUFS_I(inode)->i_gang;
 		if (!gang)
 			return -EINVAL;
 		mutex_lock(&gang->aff_mutex);
@@ -455,6 +477,8 @@ spufs_create_context(struct inode *inode, struct dentry *dentry,
 out_aff_unlock:
 	if (affinity)
 		mutex_unlock(&gang->aff_mutex);
+	if (ret && gang)
+		gang->alive--; // can't reach 0
 	return ret;
 }
 
@@ -484,6 +508,7 @@ spufs_mkgang(struct inode *dir, struct dentry *dentry, umode_t mode)
 	inode->i_fop = &simple_dir_operations;
 
 	d_instantiate(dentry, inode);
+	dget(dentry);
 	inc_nlink(dir);
 	inc_nlink(d_inode(dentry));
 	return ret;
@@ -494,6 +519,21 @@ spufs_mkgang(struct inode *dir, struct dentry *dentry, umode_t mode)
 	return ret;
 }
 
+static int spufs_gang_close(struct inode *inode, struct file *file)
+{
+	unuse_gang(file->f_path.dentry);
+	return dcache_dir_close(inode, file);
+}
+
+static const struct file_operations spufs_gang_fops = {
+	.open		= dcache_dir_open,
+	.release	= spufs_gang_close,
+	.llseek		= dcache_dir_lseek,
+	.read		= generic_read_dir,
+	.iterate_shared	= dcache_readdir,
+	.fsync		= noop_fsync,
+};
+
 static int spufs_gang_open(const struct path *path)
 {
 	int ret;
@@ -513,7 +553,7 @@ static int spufs_gang_open(const struct path *path)
 		return PTR_ERR(filp);
 	}
 
-	filp->f_op = &simple_dir_operations;
+	filp->f_op = &spufs_gang_fops;
 	fd_install(ret, filp);
 	return ret;
 }
@@ -528,10 +568,8 @@ static int spufs_create_gang(struct inode *inode,
 	ret = spufs_mkgang(inode, dentry, mode & 0777);
 	if (!ret) {
 		ret = spufs_gang_open(&path);
-		if (ret < 0) {
-			int err = simple_rmdir(inode, dentry);
-			WARN_ON(err);
-		}
+		if (ret < 0)
+			unuse_gang(dentry);
 	}
 	return ret;
 }

arch/powerpc/platforms/cell/spufs/spufs.h

@@ -151,6 +151,8 @@ struct spu_gang {
 	int aff_flags;
 	struct spu *aff_ref_spu;
 	atomic_t aff_sched_count;
+
+	int alive;
 };
 
 /* Flag bits for spu_gang aff_flags */