[PATCH v5 1/7] eventfs: Remove "is_freed" union with rcu head

Steven Rostedt
2023-10-31T22:34:28Z

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.

Cc: stable@vger.kernel.org
Fixes: 63940449555e7 ("eventfs: Implement eventfs lookup, read, open functions")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.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 754885dfe71c..2c2c75b2ad73 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