kernfs: replace kernfs_node->u.completion with kernfs_root->deactivate_waitq

kernfs_node->u.completion is used to notify deactivation completion
from kernfs_put_active() to kernfs_deactivate().  We now allow
multiple racing removals of the same node and the current removal
scheme is no longer correct - kernfs_remove() invocation may return
before the node is properly deactivated if it races against another
removal.  The removal path will be restructured to address the issue.

To help such restructure which requires supporting multiple waiters,
this patch replaces kernfs_node->u.completion with
kernfs_root->deactivate_waitq.  This makes deactivation event
notifications share a per-root waitqueue_head; however, the wait path
is quite cold and this will also allow shaving one pointer off
kernfs_node.

Signed-off-by: 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 510b5062ef302184736503ec076d9ffafdb136aa..ed62de6cdf8fd2d1fd2caf0a90a36882fad86d55 100644 (file)
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -8,6 +8,7 @@
  * This file is released under the GPLv2.
  */
 
+#include <linux/sched.h>
 #include <linux/fs.h>
 #include <linux/namei.h>
 #include <linux/idr.h>
@@ -151,6 +152,7 @@ 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))
@@ -162,11 +164,7 @@ void kernfs_put_active(struct kernfs_node *kn)
        if (likely(v != KN_DEACTIVATED_BIAS))
                return;
 
-       /*
-        * atomic_dec_return() is a mb(), we'll always see the updated
-        * kn->u.completion.
-        */
-       complete(kn->u.completion);
+       wake_up_all(&root->deactivate_waitq);
 }
 
 /**
@@ -177,26 +175,22 @@ void kernfs_put_active(struct kernfs_node *kn)
  */
 static void kernfs_deactivate(struct kernfs_node *kn)
 {
-       DECLARE_COMPLETION_ONSTACK(wait);
-       int v;
+       struct kernfs_root *root = kernfs_root(kn);
 
        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);
 
-       if (v != KN_DEACTIVATED_BIAS) {
+       atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
+
+       if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
                lock_contended(&kn->dep_map, _RET_IP_);
-               wait_for_completion(&wait);
-       }
+
+       wait_event(root->deactivate_waitq,
+                  atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
 
        lock_acquired(&kn->dep_map, _RET_IP_);
        rwsem_release(&kn->dep_map, 1, _RET_IP_);
@@ -613,6 +607,7 @@ 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 d2c439db4efa2b7e8654608834858e4521d7970b..232f1a632383f537363eabda683c851fc0a4c486 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/completion.h>
+#include <linux/wait.h>
 
 struct file;
 struct iattr;
@@ -91,7 +91,6 @@ struct kernfs_node {
        struct rb_node          rb;
 
        union {
-               struct completion       *completion;
                struct kernfs_node      *removed_list;
        } u;
 
@@ -132,6 +131,7 @@ 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 {