Re: [PATCH 2/2] tracefs: Don't overlay 'struct inode'
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2024-08-07 15:49:51
Also in:
lkml
Subsystem:
filesystems (vfs and infrastructure), the rest, tracing · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
On Wed, 7 Aug 2024 14:44:53 +0100 Al Viro [off-list ref] wrote:
On Wed, Aug 07, 2024 at 09:35:45AM -0400, Steven Rostedt wrote:quoted
Perhaps:diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h index f704d8348357..ab6d6c3d835d 100644 --- a/fs/tracefs/internal.h +++ b/fs/tracefs/internal.h@@ -10,12 +10,12 @@ enum { }; struct tracefs_inode { + struct inode vfs_inode; + /* The below gets initialized with memset_after(ti, 0, vfs_inode) */ union { - struct inode vfs_inode; + struct list_head list; struct rcu_head rcu; }; - /* The below gets initialized with memset_after(ti, 0, vfs_inode) */ - struct list_head list; unsigned long flags; void *private; };Your current variant gives you an RCU-delayed call of tracefs_free_inode(), which schedules an RCU-delayed call of tracefs_free_inode_rcu(). Do you really need that double RCU delay to start with? Because if you do not, just do that list_del_rcu() in ->destroy_inode() (which is called without an RCU delay) and have kmem_cache_free() in ->free_inode() (which is called *with* RCU delay started after the call of ->destroy_inode()).
Thanks, I didn't know about these. So I could use destroy_inode() for the removing of the link list, and then free_inode to free it. Something like:
diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 1028ab6d9a74..ae2cb2221acd 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c@@ -53,15 +53,14 @@ static struct inode *tracefs_alloc_inode(struct super_block *sb) return &ti->vfs_inode; } -static void tracefs_free_inode_rcu(struct rcu_head *rcu) +static void tracefs_free_inode(struct inode *inode) { - struct tracefs_inode *ti; + struct tracefs_inode *ti = get_tracefs(inode); - ti = container_of(rcu, struct tracefs_inode, rcu); kmem_cache_free(tracefs_inode_cachep, ti); } -static void tracefs_free_inode(struct inode *inode) +static void tracefs_destroy_inode(struct inode *inode) { struct tracefs_inode *ti = get_tracefs(inode); unsigned long flags;
@@ -69,8 +68,6 @@ static void tracefs_free_inode(struct inode *inode) spin_lock_irqsave(&tracefs_inode_lock, flags); list_del_rcu(&ti->list); spin_unlock_irqrestore(&tracefs_inode_lock, flags); - - call_rcu(&ti->rcu, tracefs_free_inode_rcu); } static ssize_t default_read_file(struct file *file, char __user *buf,
@@ -437,6 +434,7 @@ static int tracefs_drop_inode(struct inode *inode) static const struct super_operations tracefs_super_operations = { .alloc_inode = tracefs_alloc_inode, .free_inode = tracefs_free_inode, + .destroy_inode = tracefs_destroy_inode, .drop_inode = tracefs_drop_inode, .statfs = simple_statfs, .show_options = tracefs_show_options,
diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index f704d8348357..d83c2a25f288 100644
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h@@ -10,10 +10,7 @@ enum { }; struct tracefs_inode { - union { - struct inode vfs_inode; - struct rcu_head rcu; - }; + struct inode vfs_inode; /* The below gets initialized with memset_after(ti, 0, vfs_inode) */ struct list_head list; unsigned long flags;
I'll run this under some more tests and see if it doesn't crash. I'll apply the first patch of this series too, and then probably use this one. -- Steve