linux-kernel - [tip: sched/psi] kernfs: Add KERNFS

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Date:   Fri, 09 Sep 2022 14:00:28 -0000
From:   "tip-bot2 for Tejun Heo" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Chengming Zhou <zhouchengming@...edance.com>,
        Tejun Heo <tj@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/psi] kernfs: Add KERNFS_REMOVING flags

The following commit has been merged into the sched/psi branch of tip:

Commit-ID:     c25491747b21536bd56dccb82a109754bbc8d52c
Gitweb:        https://git.kernel.org/tip/c25491747b21536bd56dccb82a109754bbc8d52c
Author:        Tejun Heo <tj@...nel.org>
AuthorDate:    Sat, 27 Aug 2022 19:04:37 -10:00
Committer:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CommitterDate: Thu, 01 Sep 2022 18:08:44 +02:00

kernfs: Add KERNFS_REMOVING flags

KERNFS_ACTIVATED tracks whether a given node has ever been activated. As a
node was only deactivated on removal, this was used for

 1. Drain optimization (removed by the previous patch).
 2. To hide !activated nodes
 3. To avoid double activations
 4. Reject adding children to a node being removed
 5. Skip activaing a node which is being removed.

We want to decouple deactivation from removal so that nodes can be
deactivated and hidden dynamically, which makes KERNFS_ACTIVATED useless for
all of the above purposes.

#1 is already gone. #2 and #3 can instead test whether the node is currently
active. A new flag KERNFS_REMOVING is added to explicitly mark nodes which
are being removed for #4 and #5.

While this leaves KERNFS_ACTIVATED with no users, leave it be as it will be
used in a following patch.

Cc: Chengming Zhou <zhouchengming@...edance.com>
Tested-by: Chengming Zhou <zhouchengming@...edance.com>
Reviewed-by: Chengming Zhou <zhouchengming@...edance.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
Link: https://lore.kernel.org/r/20220828050440.734579-7-tj@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/kernfs/dir.c        | 21 +++++++--------------
 include/linux/kernfs.h |  1 +
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index b3d2018..f8cbd05 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -705,13 +705,7 @@ struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
 			goto err_unlock;
 	}
 
-	/*
-	 * ACTIVATED is protected with kernfs_mutex but it was clear when
-	 * @kn was added to idr and we just wanna see it set.  No need to
-	 * grab kernfs_mutex.
-	 */
-	if (unlikely(!(kn->flags & KERNFS_ACTIVATED) ||
-		     !atomic_inc_not_zero(&kn->count)))
+	if (unlikely(!kernfs_active(kn) || !atomic_inc_not_zero(&kn->count)))
 		goto err_unlock;
 
 	spin_unlock(&kernfs_idr_lock);
@@ -753,10 +747,7 @@ int kernfs_add_one(struct kernfs_node *kn)
 		goto out_unlock;
 
 	ret = -ENOENT;
-	if (parent->flags & KERNFS_EMPTY_DIR)
-		goto out_unlock;
-
-	if ((parent->flags & KERNFS_ACTIVATED) && !kernfs_active(parent))
+	if (parent->flags & (KERNFS_REMOVING | KERNFS_EMPTY_DIR))
 		goto out_unlock;
 
 	kn->hash = kernfs_name_hash(kn->name, kn->ns);
@@ -1336,7 +1327,7 @@ void kernfs_activate(struct kernfs_node *kn)
 
 	pos = NULL;
 	while ((pos = kernfs_next_descendant_post(pos, kn))) {
-		if (pos->flags & KERNFS_ACTIVATED)
+		if (kernfs_active(pos) || (pos->flags & KERNFS_REMOVING))
 			continue;
 
 		WARN_ON_ONCE(pos->parent && RB_EMPTY_NODE(&pos->rb));
@@ -1368,11 +1359,13 @@ static void __kernfs_remove(struct kernfs_node *kn)
 
 	pr_debug("kernfs %s: removing\n", kn->name);
 
-	/* prevent any new usage under @kn by deactivating all nodes */
+	/* prevent new usage by marking all nodes removing and deactivating */
 	pos = NULL;
-	while ((pos = kernfs_next_descendant_post(pos, kn)))
+	while ((pos = kernfs_next_descendant_post(pos, kn))) {
+		pos->flags |= KERNFS_REMOVING;
 		if (kernfs_active(pos))
 			atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
+	}
 
 	/* deactivate and unlink the subtree node-by-node */
 	do {
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 367044d..b77d257 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -112,6 +112,7 @@ enum kernfs_node_flag {
 	KERNFS_SUICIDED		= 0x0800,
 	KERNFS_EMPTY_DIR	= 0x1000,
 	KERNFS_HAS_RELEASE	= 0x2000,
+	KERNFS_REMOVING		= 0x4000,
 };
 
 /* @flags for kernfs_create_root() */