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kernfs: Remove reference counting for kernfs_open_node. 

The decision to free kernfs_open_node object in kernfs_put_open_node can
be taken based on whether kernfs_open_node->files list is empty or not. As
far as kernfs_drain_open_files is concerned it can't overlap with
kernfs_fops_open and hence can check for ->attr.open optimistically
(if ->attr.open is NULL) or under kernfs_open_file_mutex (if it needs to
traverse the ->files list.) Thus kernfs_drain_open_files can work w/o ref
counting involved kernfs_open_node as well.
So remove ->refcnt and modify the above mentioned users accordingly.

Suggested by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Link: https://lore.kernel.org/r/20220324103040.584491-2-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Imran Khan 2022-03-24 21:30:39 +11:00 committed by Greg Kroah-Hartman
parent 6423d29510
commit bd900901b8
1 changed files with 9 additions and 14 deletions
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23
fs/kernfs/file.c
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@ -33,7 +33,6 @@ static DEFINE_SPINLOCK(kernfs_open_node_lock);
static DEFINE_MUTEX(kernfs_open_file_mutex);
struct kernfs_open_node {
atomic_t refcnt;
atomic_t event;
wait_queue_head_t poll;
struct list_head files; /* goes through kernfs_open_file.list */
@ -530,10 +529,8 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
}
on = kn->attr.open;
if (on) {
atomic_inc(&on->refcnt);
if (on)
list_add_tail(&of->list, &on->files);
}
spin_unlock_irq(&kernfs_open_node_lock);
mutex_unlock(&kernfs_open_file_mutex);
@ -548,7 +545,6 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
if (!new_on)
return -ENOMEM;
atomic_set(&new_on->refcnt, 0);
atomic_set(&new_on->event, 1);
init_waitqueue_head(&new_on->poll);
INIT_LIST_HEAD(&new_on->files);
@ -557,11 +553,12 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
/**
* kernfs_put_open_node - put kernfs_open_node
* @kn: target kernfs_nodet
* @kn: target kernfs_node
* @of: associated kernfs_open_file
*
* Put @kn->attr.open and unlink @of from the files list. If
* reference count reaches zero, disassociate and free it.
* list of associated open files becomes empty, disassociate and
* free kernfs_open_node.
*
* LOCKING:
* None.
@ -578,7 +575,7 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
if (of)
list_del(&of->list);
if (atomic_dec_and_test(&on->refcnt))
if (list_empty(&on->files))
kn->attr.open = NULL;
else
on = NULL;
@ -768,15 +765,15 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
return;
spin_lock_irq(&kernfs_open_node_lock);
on = kn->attr.open;
if (on)
atomic_inc(&on->refcnt);
spin_unlock_irq(&kernfs_open_node_lock);
if (!on)
return;
mutex_lock(&kernfs_open_file_mutex);
if (!kn->attr.open) {
mutex_unlock(&kernfs_open_file_mutex);
return;
}
list_for_each_entry(of, &on->files, list) {
struct inode *inode = file_inode(of->file);
@ -789,8 +786,6 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
}
mutex_unlock(&kernfs_open_file_mutex);
kernfs_put_open_node(kn, NULL);
}
/*