linux-kernel - [for-next][PATCH 05/12] eventfs: Remove "is

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Date:   Wed, 01 Nov 2023 17:37:23 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org, Ajay Kaher <akaher@...are.com>
Subject: [for-next][PATCH 05/12] eventfs: Remove "is_freed" union with rcu head

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

The eventfs_inode->is_freed was a union with the rcu_head with the
assumption that when it was on the srcu list the head would contain a
pointer which would make "is_freed" true. But that was a wrong assumption
as the rcu head is a single link list where the last element is NULL.

Instead, split the nr_entries integer so that "is_freed" is one bit and
the nr_entries is the next 31 bits. As there shouldn't be more than 10
(currently there's at most 5 to 7 depending on the config), this should
not be a problem.

Link: https://lkml.kernel.org/r/20231101172649.049758712@goodmis.org

Cc: stable@...r.kernel.org
Cc: Mark Rutland <mark.rutland@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ajay Kaher <akaher@...are.com>
Fixes: 63940449555e7 ("eventfs: Implement eventfs lookup, read, open functions")
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 fs/tracefs/event_inode.c | 2 ++
 fs/tracefs/internal.h    | 6 +++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 9f612a8f009d..1ce73acf3df0 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -824,6 +824,8 @@ static void eventfs_remove_rec(struct eventfs_inode *ei, struct list_head *head,
 		eventfs_remove_rec(ei_child, head, level + 1);
 	}
 
+	ei->is_freed = 1;
+
 	list_del_rcu(&ei->list);
 	list_add_tail(&ei->del_list, head);
 }
diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index 64fde9490f52..c7d88aaa949f 100644
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h
@@ -23,6 +23,7 @@ struct tracefs_inode {
  * @d_parent:   pointer to the parent's dentry
  * @d_children: The array of dentries to represent the files when created
  * @data:	The private data to pass to the callbacks
+ * @is_freed:	Flag set if the eventfs is on its way to be freed
  * @nr_entries: The number of items in @entries
  */
 struct eventfs_inode {
@@ -38,14 +39,13 @@ struct eventfs_inode {
 	 * Union - used for deletion
 	 * @del_list:	list of eventfs_inode to delete
 	 * @rcu:	eventfs_inode to delete in RCU
-	 * @is_freed:	node is freed if one of the above is set
 	 */
 	union {
 		struct list_head	del_list;
 		struct rcu_head		rcu;
-		unsigned long		is_freed;
 	};
-	int				nr_entries;
+	unsigned int			is_freed:1;
+	unsigned int			nr_entries:31;
 };
 
 static inline struct tracefs_inode *get_tracefs(const struct inode *inode)
-- 
2.42.0