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

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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>
This commit is contained in:
Tejun Heo 2014-01-10 08:57:19 -05:00 committed by Greg Kroah-Hartman
parent d92d2e6bd7
commit ea1c472dfe
2 changed files with 13 additions and 18 deletions
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27
fs/kernfs/dir.c
View File

@ -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;
}

4
include/linux/kernfs.h
View File

@ -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 {