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 ed62de6cdf8fd2d1fd2caf0a90a36882fad86d55..510b5062ef302184736503ec076d9ffafdb136aa 100644 (file)
--- 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 @@ struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
  */
 void kernfs_put_active(struct kernfs_node *kn)
 {
-       struct kernfs_root *root = kernfs_root(kn);
        int v;
 
        if (unlikely(!kn))
@@ -164,7 +162,11 @@ void kernfs_put_active(struct kernfs_node *kn)
        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 @@ void kernfs_put_active(struct kernfs_node *kn)
  */
 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;
 
-       rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
+       kn->u.completion = (void *)&wait;
 
-       atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
+       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);
 
-       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 @@ struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
 
        root->dir_ops = kdops;
        root->kn = kn;
-       init_waitqueue_head(&root->deactivate_waitq);
 
        return root;
 }

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 232f1a632383f537363eabda683c851fc0a4c486..d2c439db4efa2b7e8654608834858e4521d7970b 100644 (file)
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -15,7 +15,7 @@
 #include <linux/lockdep.h>
 #include <linux/rbtree.h>
 #include <linux/atomic.h>
-#include <linux/wait.h>
+#include <linux/completion.h>
 
 struct file;
 struct iattr;
@@ -91,6 +91,7 @@ struct kernfs_node {
        struct rb_node          rb;
 
        union {
+               struct completion       *completion;
                struct kernfs_node      *removed_list;
        } u;
 
@@ -131,7 +132,6 @@ struct kernfs_root {
        /* private fields, do not use outside kernfs proper */
        struct ida              ino_ida;
        struct kernfs_dir_ops   *dir_ops;
-       wait_queue_head_t       deactivate_waitq;
 };
 
 struct kernfs_open_file {