Revert "kernfs: replace kernfs_node->u.completion with kernfs_root->deactivate_waitq"
This reverts commit ea1c472dfeada211a0100daa7976e8e8e779b858.
Tejun writes:
I'm sorry but can you please revert the whole series?
get_active() waiting while a node is deactivated has potential
to lead to deadlock and that deactivate/reactivate interface is
something fundamentally flawed and that cgroup will have to work
with the remove_self() like everybody else. IOW, I think the
first posting was correct.
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index ed62de6..510b506 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -8,7 +8,6 @@
* This file is released under the GPLv2.
*/
-#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/idr.h>
@@ -152,7 +151,6 @@
*/
void kernfs_put_active(struct kernfs_node *kn)
{
- struct kernfs_root *root = kernfs_root(kn);
int v;
if (unlikely(!kn))
@@ -164,7 +162,11 @@
if (likely(v != KN_DEACTIVATED_BIAS))
return;
- wake_up_all(&root->deactivate_waitq);
+ /*
+ * atomic_dec_return() is a mb(), we'll always see the updated
+ * kn->u.completion.
+ */
+ complete(kn->u.completion);
}
/**
@@ -175,22 +177,26 @@
*/
static void kernfs_deactivate(struct kernfs_node *kn)
{
- struct kernfs_root *root = kernfs_root(kn);
+ DECLARE_COMPLETION_ONSTACK(wait);
+ int v;
BUG_ON(!(kn->flags & KERNFS_REMOVED));
if (!(kernfs_type(kn) & KERNFS_ACTIVE_REF))
return;
+ kn->u.completion = (void *)&wait;
+
rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
+ /* atomic_add_return() is a mb(), put_active() will always see
+ * the updated kn->u.completion.
+ */
+ v = atomic_add_return(KN_DEACTIVATED_BIAS, &kn->active);
- atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
-
- if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
+ if (v != KN_DEACTIVATED_BIAS) {
lock_contended(&kn->dep_map, _RET_IP_);
-
- wait_event(root->deactivate_waitq,
- atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
+ wait_for_completion(&wait);
+ }
lock_acquired(&kn->dep_map, _RET_IP_);
rwsem_release(&kn->dep_map, 1, _RET_IP_);
@@ -607,7 +613,6 @@
root->dir_ops = kdops;
root->kn = kn;
- init_waitqueue_head(&root->deactivate_waitq);
return root;
}