Re: [PATCH v5 1/7] eventfs: Remove "is_freed" union with rcu head
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Date: 2023-11-01 12:20:09
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On Tue, 31 Oct 2023 18:33:27 -0400 Steven Rostedt [off-list ref] wrote:
From: "Steven Rostedt (Google)" <rostedt@goodmis.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.
Yeah, even 16 bit nr_entries is enough.. (maybe the biggest user is syscall event group) Looks good to me. Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Thank you,
quoted hunk ↗ jump to hunk
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
-- Masami Hiramatsu (Google) [off-list ref]