kernfs: switch kernfs to use an rwsem

The kernfs global lock restricts the ability to perform kernfs node
lookup operations in parallel during path walks.

Change the kernfs mutex to an rwsem so that, when opportunity arises,
node searches can be done in parallel with path walk lookups.

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/162642770946.63632.2218304587223241374.stgit@web.messagingengine.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 50 insertions, 50 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 0b21a8f961ac..4994723d6cf7 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -17,7 +17,7 @@
 
 #include "kernfs-internal.h"
 
-DEFINE_MUTEX(kernfs_mutex);
+DECLARE_RWSEM(kernfs_rwsem);
 static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
 static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by rename_lock */
 static DEFINE_SPINLOCK(kernfs_idr_lock);	/* root->ino_idr */
@@ -26,7 +26,7 @@ static DEFINE_SPINLOCK(kernfs_idr_lock);	/* root->ino_idr */
 
 static bool kernfs_active(struct kernfs_node *kn)
 {
-	lockdep_assert_held(&kernfs_mutex);
+	lockdep_assert_held(&kernfs_rwsem);
 	return atomic_read(&kn->active) >= 0;
 }
 
@@ -340,7 +340,7 @@ static int kernfs_sd_compare(const struct kernfs_node *left,
  *	@kn->parent->dir.children.
  *
  *	Locking:
- *	mutex_lock(kernfs_mutex)
+ *	kernfs_rwsem held exclusive
  *
  *	RETURNS:
  *	0 on susccess -EEXIST on failure.
@@ -386,7 +386,7 @@ static int kernfs_link_sibling(struct kernfs_node *kn)
  *	removed, %false if @kn wasn't on the rbtree.
  *
  *	Locking:
- *	mutex_lock(kernfs_mutex)
+ *	kernfs_rwsem held exclusive
  */
 static bool kernfs_unlink_sibling(struct kernfs_node *kn)
 {
@@ -457,14 +457,14 @@ void kernfs_put_active(struct kernfs_node *kn)
  * return after draining is complete.
  */
 static void kernfs_drain(struct kernfs_node *kn)
-	__releases(&kernfs_mutex) __acquires(&kernfs_mutex)
+	__releases(&kernfs_rwsem) __acquires(&kernfs_rwsem)
 {
 	struct kernfs_root *root = kernfs_root(kn);
 
-	lockdep_assert_held(&kernfs_mutex);
+	lockdep_assert_held_write(&kernfs_rwsem);
 	WARN_ON_ONCE(kernfs_active(kn));
 
-	mutex_unlock(&kernfs_mutex);
+	up_write(&kernfs_rwsem);
 
 	if (kernfs_lockdep(kn)) {
 		rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
@@ -483,7 +483,7 @@ static void kernfs_drain(struct kernfs_node *kn)
 
 	kernfs_drain_open_files(kn);
 
-	mutex_lock(&kernfs_mutex);
+	down_write(&kernfs_rwsem);
 }
 
 /**
@@ -722,7 +722,7 @@ int kernfs_add_one(struct kernfs_node *kn)
 	bool has_ns;
 	int ret;
 
-	mutex_lock(&kernfs_mutex);
+	down_write(&kernfs_rwsem);
 
 	ret = -EINVAL;
 	has_ns = kernfs_ns_enabled(parent);
@@ -753,7 +753,7 @@ int kernfs_add_one(struct kernfs_node *kn)
 		ps_iattr->ia_mtime = ps_iattr->ia_ctime;
 	}
 
-	mutex_unlock(&kernfs_mutex);
+	up_write(&kernfs_rwsem);
 
 	/*
 	 * Activate the new node unless CREATE_DEACTIVATED is requested.
@@ -767,7 +767,7 @@ int kernfs_add_one(struct kernfs_node *kn)
 	return 0;
 
 out_unlock:
-	mutex_unlock(&kernfs_mutex);
+	up_write(&kernfs_rwsem);
 	return ret;
 }
 
@@ -788,7 +788,7 @@ static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
 	bool has_ns = kernfs_ns_enabled(parent);
 	unsigned int hash;
 
-	lockdep_assert_held(&kernfs_mutex);
+	lockdep_assert_held(&kernfs_rwsem);
 
 	if (has_ns != (bool)ns) {
 		WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
@@ -820,7 +820,7 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
 	size_t len;
 	char *p, *name;
 
-	lockdep_assert_held(&kernfs_mutex);
+	lockdep_assert_held_read(&kernfs_rwsem);
 
 	/* grab kernfs_rename_lock to piggy back on kernfs_pr_cont_buf */
 	spin_lock_irq(&kernfs_rename_lock);
@@ -860,10 +860,10 @@ struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
 {
 	struct kernfs_node *kn;
 
-	mutex_lock(&kernfs_mutex);
+	down_read(&kernfs_rwsem);
 	kn = kernfs_find_ns(parent, name, ns);
 	kernfs_get(kn);
-	mutex_unlock(&kernfs_mutex);
+	up_read(&kernfs_rwsem);
 
 	return kn;
 }
@@ -884,10 +884,10 @@ struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
 {
 	struct kernfs_node *kn;
 
-	mutex_lock(&kernfs_mutex);
+	down_read(&kernfs_rwsem);
 	kn = kernfs_walk_ns(parent, path, ns);
 	kernfs_get(kn);
-	mutex_unlock(&kernfs_mutex);
+	up_read(&kernfs_rwsem);
 
 	return kn;
 }
@@ -1046,18 +1046,18 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
 		/* If the kernfs parent node has changed discard and
 		 * proceed to ->lookup.
 		 */
-		mutex_lock(&kernfs_mutex);
+		down_read(&kernfs_rwsem);
 		spin_lock(&dentry->d_lock);
 		parent = kernfs_dentry_node(dentry->d_parent);
 		if (parent) {
 			if (kernfs_dir_changed(parent, dentry)) {
 				spin_unlock(&dentry->d_lock);
-				mutex_unlock(&kernfs_mutex);
+				up_read(&kernfs_rwsem);
 				return 0;
 			}
 		}
 		spin_unlock(&dentry->d_lock);
-		mutex_unlock(&kernfs_mutex);
+		up_read(&kernfs_rwsem);
 
 		/* The kernfs parent node hasn't changed, leave the
 		 * dentry negative and return success.
@@ -1066,7 +1066,7 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
 	}
 
 	kn = kernfs_dentry_node(dentry);
-	mutex_lock(&kernfs_mutex);
+	down_read(&kernfs_rwsem);
 
 	/* The kernfs node has been deactivated */
 	if (!kernfs_active(kn))
@@ -1085,10 +1085,10 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
 	    kernfs_info(dentry->d_sb)->ns != kn->ns)
 		goto out_bad;
 
-	mutex_unlock(&kernfs_mutex);
+	up_read(&kernfs_rwsem);
 	return 1;
 out_bad:
-	mutex_unlock(&kernfs_mutex);
+	up_read(&kernfs_rwsem);
 	return 0;
 }
 
@@ -1106,7 +1106,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
 	struct inode *inode = NULL;
 	const void *ns = NULL;
 
-	mutex_lock(&kernfs_mutex);
+	down_read(&kernfs_rwsem);
 	if (kernfs_ns_enabled(parent))
 		ns = kernfs_info(dir->i_sb)->ns;
 
@@ -1122,7 +1122,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
 		kernfs_set_rev(parent, dentry);
 	/* instantiate and hash (possibly negative) dentry */
 	ret = d_splice_alias(inode, dentry);
-	mutex_unlock(&kernfs_mutex);
+	up_read(&kernfs_rwsem);
 
 	return ret;
 }
@@ -1244,7 +1244,7 @@ static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
 {
 	struct rb_node *rbn;
 
-	lockdep_assert_held(&kernfs_mutex);
+	lockdep_assert_held_write(&kernfs_rwsem);
 
 	/* if first iteration, visit leftmost descendant which may be root */
 	if (!pos)
@@ -1280,7 +1280,7 @@ void kernfs_activate(struct kernfs_node *kn)
 {
 	struct kernfs_node *pos;
 
-	mutex_lock(&kernfs_mutex);
+	down_write(&kernfs_rwsem);
 
 	pos = NULL;
 	while ((pos = kernfs_next_descendant_post(pos, kn))) {
@@ -1294,14 +1294,14 @@ void kernfs_activate(struct kernfs_node *kn)
 		pos->flags |= KERNFS_ACTIVATED;
 	}
 
-	mutex_unlock(&kernfs_mutex);
+	up_write(&kernfs_rwsem);
 }
 
 static void __kernfs_remove(struct kernfs_node *kn)
 {
 	struct kernfs_node *pos;
 
-	lockdep_assert_held(&kernfs_mutex);
+	lockdep_assert_held_write(&kernfs_rwsem);
 
 	/*
 	 * Short-circuit if non-root @kn has already finished removal.
@@ -1324,7 +1324,7 @@ static void __kernfs_remove(struct kernfs_node *kn)
 		pos = kernfs_leftmost_descendant(kn);
 
 		/*
-		 * kernfs_drain() drops kernfs_mutex temporarily and @pos's
+		 * kernfs_drain() drops kernfs_rwsem temporarily and @pos's
 		 * base ref could have been put by someone else by the time
 		 * the function returns.  Make sure it doesn't go away
 		 * underneath us.
@@ -1371,9 +1371,9 @@ static void __kernfs_remove(struct kernfs_node *kn)
  */
 void kernfs_remove(struct kernfs_node *kn)
 {
-	mutex_lock(&kernfs_mutex);
+	down_write(&kernfs_rwsem);
 	__kernfs_remove(kn);
-	mutex_unlock(&kernfs_mutex);
+	up_write(&kernfs_rwsem);
 }
 
 /**
@@ -1460,17 +1460,17 @@ bool kernfs_remove_self(struct kernfs_node *kn)
 {
 	bool ret;
 
-	mutex_lock(&kernfs_mutex);
+	down_write(&kernfs_rwsem);
 	kernfs_break_active_protection(kn);
 
 	/*
 	 * SUICIDAL is used to arbitrate among competing invocations.  Only
 	 * the first one will actually perform removal.  When the removal
 	 * is complete, SUICIDED is set and the active ref is restored
-	 * while holding kernfs_mutex.  The ones which lost arbitration
-	 * waits for SUICDED && drained which can happen only after the
-	 * enclosing kernfs operation which executed the winning instance
-	 * of kernfs_remove_self() finished.
+	 * while kernfs_rwsem for held exclusive.  The ones which lost
+	 * arbitration waits for SUICIDED && drained which can happen only
+	 * after the enclosing kernfs operation which executed the winning
+	 * instance of kernfs_remove_self() finished.
 	 */
 	if (!(kn->flags & KERNFS_SUICIDAL)) {
 		kn->flags |= KERNFS_SUICIDAL;
@@ -1488,9 +1488,9 @@ bool kernfs_remove_self(struct kernfs_node *kn)
 			    atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
 				break;
 
-			mutex_unlock(&kernfs_mutex);
+			up_write(&kernfs_rwsem);
 			schedule();
-			mutex_lock(&kernfs_mutex);
+			down_write(&kernfs_rwsem);
 		}
 		finish_wait(waitq, &wait);
 		WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
@@ -1498,12 +1498,12 @@ bool kernfs_remove_self(struct kernfs_node *kn)
 	}
 
 	/*
-	 * This must be done while holding kernfs_mutex; otherwise, waiting
-	 * for SUICIDED && deactivated could finish prematurely.
+	 * This must be done while kernfs_rwsem held exclusive; otherwise,
+	 * waiting for SUICIDED && deactivated could finish prematurely.
 	 */
 	kernfs_unbreak_active_protection(kn);
 
-	mutex_unlock(&kernfs_mutex);
+	up_write(&kernfs_rwsem);
 	return ret;
 }
 
@@ -1527,13 +1527,13 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
 		return -ENOENT;
 	}
 
-	mutex_lock(&kernfs_mutex);
+	down_write(&kernfs_rwsem);
 
 	kn = kernfs_find_ns(parent, name, ns);
 	if (kn)
 		__kernfs_remove(kn);
 
-	mutex_unlock(&kernfs_mutex);
+	up_write(&kernfs_rwsem);
 
 	if (kn)
 		return 0;
@@ -1559,7 +1559,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 	if (!kn->parent)
 		return -EINVAL;
 
-	mutex_lock(&kernfs_mutex);
+	down_write(&kernfs_rwsem);
 
 	error = -ENOENT;
 	if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
@@ -1613,7 +1613,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 
 	error = 0;
  out:
-	mutex_unlock(&kernfs_mutex);
+	up_write(&kernfs_rwsem);
 	return error;
 }
 
@@ -1688,7 +1688,7 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
 
 	if (!dir_emit_dots(file, ctx))
 		return 0;
-	mutex_lock(&kernfs_mutex);
+	down_read(&kernfs_rwsem);
 
 	if (kernfs_ns_enabled(parent))
 		ns = kernfs_info(dentry->d_sb)->ns;
@@ -1705,12 +1705,12 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
 		file->private_data = pos;
 		kernfs_get(pos);
 
-		mutex_unlock(&kernfs_mutex);
+		up_read(&kernfs_rwsem);
 		if (!dir_emit(ctx, name, len, ino, type))
 			return 0;
-		mutex_lock(&kernfs_mutex);
+		down_read(&kernfs_rwsem);
 	}
-	mutex_unlock(&kernfs_mutex);
+	up_read(&kernfs_rwsem);
 	file->private_data = NULL;
 	ctx->pos = INT_MAX;
 	return 0;