kernfs: switch global kernfs_rwsem lock to per-fs lock

The kernfs implementation has big lock granularity(kernfs_rwsem) so
every kernfs-based(e.g., sysfs, cgroup) fs are able to compete the
lock. It makes trouble for some cases to wait the global lock
for a long time even though they are totally independent contexts
each other.

A general example is process A goes under direct reclaim with holding
the lock when it accessed the file in sysfs and process B is waiting
the lock with exclusive mode and then process C is waiting the lock
until process B could finish the job after it gets the lock from
process A.

This patch switches the global kernfs_rwsem to per-fs lock, which
put the rwsem into kernfs_root.

Suggested-by: Tejun Heo <tj@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Link: https://lore.kernel.org/r/20211118230008.2679780-1-minchan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 8e0a137..13cae0c 100644 (file)
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -17,7 +17,6 @@
 
 #include "kernfs-internal.h"
 
-DECLARE_RWSEM(kernfs_rwsem);
 static DEFINE_SPINLOCK(kernfs_rename_lock);    /* kn->parent and ->name */
 static char kernfs_pr_cont_buf[PATH_MAX];      /* protected by rename_lock */
 static DEFINE_SPINLOCK(kernfs_idr_lock);       /* root->ino_idr */
@@ -26,7 +25,7 @@ static DEFINE_SPINLOCK(kernfs_idr_lock);      /* root->ino_idr */
 
 static bool kernfs_active(struct kernfs_node *kn)
 {
-       lockdep_assert_held(&kernfs_rwsem);
+       lockdep_assert_held(&kernfs_root(kn)->kernfs_rwsem);
        return atomic_read(&kn->active) >= 0;
 }
 
@@ -457,14 +456,15 @@ void kernfs_put_active(struct kernfs_node *kn)
  * return after draining is complete.
  */
 static void kernfs_drain(struct kernfs_node *kn)
-       __releases(&kernfs_rwsem) __acquires(&kernfs_rwsem)
+       __releases(&kernfs_root(kn)->kernfs_rwsem)
+       __acquires(&kernfs_root(kn)->kernfs_rwsem)
 {
        struct kernfs_root *root = kernfs_root(kn);
 
-       lockdep_assert_held_write(&kernfs_rwsem);
+       lockdep_assert_held_write(&root->kernfs_rwsem);
        WARN_ON_ONCE(kernfs_active(kn));
 
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
 
        if (kernfs_lockdep(kn)) {
                rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
@@ -483,7 +483,7 @@ static void kernfs_drain(struct kernfs_node *kn)
 
        kernfs_drain_open_files(kn);
 
-       down_write(&kernfs_rwsem);
+       down_write(&root->kernfs_rwsem);
 }
 
 /**
@@ -718,11 +718,12 @@ err_unlock:
 int kernfs_add_one(struct kernfs_node *kn)
 {
        struct kernfs_node *parent = kn->parent;
+       struct kernfs_root *root = kernfs_root(parent);
        struct kernfs_iattrs *ps_iattr;
        bool has_ns;
        int ret;
 
-       down_write(&kernfs_rwsem);
+       down_write(&root->kernfs_rwsem);
 
        ret = -EINVAL;
        has_ns = kernfs_ns_enabled(parent);
@@ -753,7 +754,7 @@ int kernfs_add_one(struct kernfs_node *kn)
                ps_iattr->ia_mtime = ps_iattr->ia_ctime;
        }
 
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
 
        /*
         * Activate the new node unless CREATE_DEACTIVATED is requested.
@@ -767,7 +768,7 @@ int kernfs_add_one(struct kernfs_node *kn)
        return 0;
 
 out_unlock:
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
        return ret;
 }
 
@@ -788,7 +789,7 @@ static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
        bool has_ns = kernfs_ns_enabled(parent);
        unsigned int hash;
 
-       lockdep_assert_held(&kernfs_rwsem);
+       lockdep_assert_held(&kernfs_root(parent)->kernfs_rwsem);
 
        if (has_ns != (bool)ns) {
                WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
@@ -820,7 +821,7 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
        size_t len;
        char *p, *name;
 
-       lockdep_assert_held_read(&kernfs_rwsem);
+       lockdep_assert_held_read(&kernfs_root(parent)->kernfs_rwsem);
 
        /* grab kernfs_rename_lock to piggy back on kernfs_pr_cont_buf */
        spin_lock_irq(&kernfs_rename_lock);
@@ -859,11 +860,12 @@ struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
                                           const char *name, const void *ns)
 {
        struct kernfs_node *kn;
+       struct kernfs_root *root = kernfs_root(parent);
 
-       down_read(&kernfs_rwsem);
+       down_read(&root->kernfs_rwsem);
        kn = kernfs_find_ns(parent, name, ns);
        kernfs_get(kn);
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
 
        return kn;
 }
@@ -883,11 +885,12 @@ struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
                                           const char *path, const void *ns)
 {
        struct kernfs_node *kn;
+       struct kernfs_root *root = kernfs_root(parent);
 
-       down_read(&kernfs_rwsem);
+       down_read(&root->kernfs_rwsem);
        kn = kernfs_walk_ns(parent, path, ns);
        kernfs_get(kn);
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
 
        return kn;
 }
@@ -912,6 +915,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
                return ERR_PTR(-ENOMEM);
 
        idr_init(&root->ino_idr);
+       init_rwsem(&root->kernfs_rwsem);
        INIT_LIST_HEAD(&root->supers);
 
        /*
@@ -1035,6 +1039,7 @@ struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
 static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
 {
        struct kernfs_node *kn;
+       struct kernfs_root *root;
 
        if (flags & LOOKUP_RCU)
                return -ECHILD;
@@ -1046,18 +1051,19 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
                /* If the kernfs parent node has changed discard and
                 * proceed to ->lookup.
                 */
-               down_read(&kernfs_rwsem);
                spin_lock(&dentry->d_lock);
                parent = kernfs_dentry_node(dentry->d_parent);
                if (parent) {
+                       spin_unlock(&dentry->d_lock);
+                       root = kernfs_root(parent);
+                       down_read(&root->kernfs_rwsem);
                        if (kernfs_dir_changed(parent, dentry)) {
-                               spin_unlock(&dentry->d_lock);
-                               up_read(&kernfs_rwsem);
+                               up_read(&root->kernfs_rwsem);
                                return 0;
                        }
-               }
-               spin_unlock(&dentry->d_lock);
-               up_read(&kernfs_rwsem);
+                       up_read(&root->kernfs_rwsem);
+               } else
+                       spin_unlock(&dentry->d_lock);
 
                /* The kernfs parent node hasn't changed, leave the
                 * dentry negative and return success.
@@ -1066,7 +1072,8 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
        }
 
        kn = kernfs_dentry_node(dentry);
-       down_read(&kernfs_rwsem);
+       root = kernfs_root(kn);
+       down_read(&root->kernfs_rwsem);
 
        /* The kernfs node has been deactivated */
        if (!kernfs_active(kn))
@@ -1085,10 +1092,10 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
            kernfs_info(dentry->d_sb)->ns != kn->ns)
                goto out_bad;
 
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
        return 1;
 out_bad:
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
        return 0;
 }
 
@@ -1102,10 +1109,12 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
 {
        struct kernfs_node *parent = dir->i_private;
        struct kernfs_node *kn;
+       struct kernfs_root *root;
        struct inode *inode = NULL;
        const void *ns = NULL;
 
-       down_read(&kernfs_rwsem);
+       root = kernfs_root(parent);
+       down_read(&root->kernfs_rwsem);
        if (kernfs_ns_enabled(parent))
                ns = kernfs_info(dir->i_sb)->ns;
 
@@ -1116,7 +1125,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
                 * create a negative.
                 */
                if (!kernfs_active(kn)) {
-                       up_read(&kernfs_rwsem);
+                       up_read(&root->kernfs_rwsem);
                        return NULL;
                }
                inode = kernfs_get_inode(dir->i_sb, kn);
@@ -1131,7 +1140,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
         */
        if (!IS_ERR(inode))
                kernfs_set_rev(parent, dentry);
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
 
        /* instantiate and hash (possibly negative) dentry */
        return d_splice_alias(inode, dentry);
@@ -1254,7 +1263,7 @@ static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
 {
        struct rb_node *rbn;
 
-       lockdep_assert_held_write(&kernfs_rwsem);
+       lockdep_assert_held_write(&kernfs_root(root)->kernfs_rwsem);
 
        /* if first iteration, visit leftmost descendant which may be root */
        if (!pos)
@@ -1289,8 +1298,9 @@ static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
 void kernfs_activate(struct kernfs_node *kn)
 {
        struct kernfs_node *pos;
+       struct kernfs_root *root = kernfs_root(kn);
 
-       down_write(&kernfs_rwsem);
+       down_write(&root->kernfs_rwsem);
 
        pos = NULL;
        while ((pos = kernfs_next_descendant_post(pos, kn))) {
@@ -1304,14 +1314,14 @@ void kernfs_activate(struct kernfs_node *kn)
                pos->flags |= KERNFS_ACTIVATED;
        }
 
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
 }
 
 static void __kernfs_remove(struct kernfs_node *kn)
 {
        struct kernfs_node *pos;
 
-       lockdep_assert_held_write(&kernfs_rwsem);
+       lockdep_assert_held_write(&kernfs_root(kn)->kernfs_rwsem);
 
        /*
         * Short-circuit if non-root @kn has already finished removal.
@@ -1381,9 +1391,11 @@ static void __kernfs_remove(struct kernfs_node *kn)
  */
 void kernfs_remove(struct kernfs_node *kn)
 {
-       down_write(&kernfs_rwsem);
+       struct kernfs_root *root = kernfs_root(kn);
+
+       down_write(&root->kernfs_rwsem);
        __kernfs_remove(kn);
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
 }
 
 /**
@@ -1469,8 +1481,9 @@ void kernfs_unbreak_active_protection(struct kernfs_node *kn)
 bool kernfs_remove_self(struct kernfs_node *kn)
 {
        bool ret;
+       struct kernfs_root *root = kernfs_root(kn);
 
-       down_write(&kernfs_rwsem);
+       down_write(&root->kernfs_rwsem);
        kernfs_break_active_protection(kn);
 
        /*
@@ -1498,9 +1511,9 @@ bool kernfs_remove_self(struct kernfs_node *kn)
                            atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
                                break;
 
-                       up_write(&kernfs_rwsem);
+                       up_write(&root->kernfs_rwsem);
                        schedule();
-                       down_write(&kernfs_rwsem);
+                       down_write(&root->kernfs_rwsem);
                }
                finish_wait(waitq, &wait);
                WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
@@ -1513,7 +1526,7 @@ bool kernfs_remove_self(struct kernfs_node *kn)
         */
        kernfs_unbreak_active_protection(kn);
 
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
        return ret;
 }
 
@@ -1530,6 +1543,7 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
                             const void *ns)
 {
        struct kernfs_node *kn;
+       struct kernfs_root *root;
 
        if (!parent) {
                WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory\n",
@@ -1537,13 +1551,14 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
                return -ENOENT;
        }
 
-       down_write(&kernfs_rwsem);
+       root = kernfs_root(parent);
+       down_write(&root->kernfs_rwsem);
 
        kn = kernfs_find_ns(parent, name, ns);
        if (kn)
                __kernfs_remove(kn);
 
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
 
        if (kn)
                return 0;
@@ -1562,6 +1577,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
                     const char *new_name, const void *new_ns)
 {
        struct kernfs_node *old_parent;
+       struct kernfs_root *root;
        const char *old_name = NULL;
        int error;
 
@@ -1569,7 +1585,8 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
        if (!kn->parent)
                return -EINVAL;
 
-       down_write(&kernfs_rwsem);
+       root = kernfs_root(kn);
+       down_write(&root->kernfs_rwsem);
 
        error = -ENOENT;
        if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
@@ -1623,7 +1640,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 
        error = 0;
  out:
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
        return error;
 }
 
@@ -1694,11 +1711,14 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
        struct dentry *dentry = file->f_path.dentry;
        struct kernfs_node *parent = kernfs_dentry_node(dentry);
        struct kernfs_node *pos = file->private_data;
+       struct kernfs_root *root;
        const void *ns = NULL;
 
        if (!dir_emit_dots(file, ctx))
                return 0;
-       down_read(&kernfs_rwsem);
+
+       root = kernfs_root(parent);
+       down_read(&root->kernfs_rwsem);
 
        if (kernfs_ns_enabled(parent))
                ns = kernfs_info(dentry->d_sb)->ns;
@@ -1715,12 +1735,12 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
                file->private_data = pos;
                kernfs_get(pos);
 
-               up_read(&kernfs_rwsem);
+               up_read(&root->kernfs_rwsem);
                if (!dir_emit(ctx, name, len, ino, type))
                        return 0;
-               down_read(&kernfs_rwsem);
+               down_read(&root->kernfs_rwsem);
        }
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
        file->private_data = NULL;
        ctx->pos = INT_MAX;
        return 0;

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 60e2a86..9414a7a 100644 (file)
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -847,6 +847,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
 {
        struct kernfs_node *kn;
        struct kernfs_super_info *info;
+       struct kernfs_root *root;
 repeat:
        /* pop one off the notify_list */
        spin_lock_irq(&kernfs_notify_lock);
@@ -859,8 +860,9 @@ repeat:
        kn->attr.notify_next = NULL;
        spin_unlock_irq(&kernfs_notify_lock);
 
+       root = kernfs_root(kn);
        /* kick fsnotify */
-       down_write(&kernfs_rwsem);
+       down_write(&root->kernfs_rwsem);
 
        list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
                struct kernfs_node *parent;
@@ -898,7 +900,7 @@ repeat:
                iput(inode);
        }
 
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
        kernfs_put(kn);
        goto repeat;
 }

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index c0eae17..3d783d8 100644 (file)
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -99,10 +99,11 @@ int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
 int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
 {
        int ret;
+       struct kernfs_root *root = kernfs_root(kn);
 
-       down_write(&kernfs_rwsem);
+       down_write(&root->kernfs_rwsem);
        ret = __kernfs_setattr(kn, iattr);
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
        return ret;
 }
 
@@ -111,12 +112,14 @@ int kernfs_iop_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 {
        struct inode *inode = d_inode(dentry);
        struct kernfs_node *kn = inode->i_private;
+       struct kernfs_root *root;
        int error;
 
        if (!kn)
                return -EINVAL;
 
-       down_write(&kernfs_rwsem);
+       root = kernfs_root(kn);
+       down_write(&root->kernfs_rwsem);
        error = setattr_prepare(&init_user_ns, dentry, iattr);
        if (error)
                goto out;
@@ -129,7 +132,7 @@ int kernfs_iop_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
        setattr_copy(&init_user_ns, inode, iattr);
 
 out:
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
        return error;
 }
 
@@ -184,13 +187,14 @@ int kernfs_iop_getattr(struct user_namespace *mnt_userns,
 {
        struct inode *inode = d_inode(path->dentry);
        struct kernfs_node *kn = inode->i_private;
+       struct kernfs_root *root = kernfs_root(kn);
 
-       down_read(&kernfs_rwsem);
+       down_read(&root->kernfs_rwsem);
        spin_lock(&inode->i_lock);
        kernfs_refresh_inode(kn, inode);
        generic_fillattr(&init_user_ns, inode, stat);
        spin_unlock(&inode->i_lock);
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
 
        return 0;
 }
@@ -274,19 +278,21 @@ int kernfs_iop_permission(struct user_namespace *mnt_userns,
                          struct inode *inode, int mask)
 {
        struct kernfs_node *kn;
+       struct kernfs_root *root;
        int ret;
 
        if (mask & MAY_NOT_BLOCK)
                return -ECHILD;
 
        kn = inode->i_private;
+       root = kernfs_root(kn);
 
-       down_read(&kernfs_rwsem);
+       down_read(&root->kernfs_rwsem);
        spin_lock(&inode->i_lock);
        kernfs_refresh_inode(kn, inode);
        ret = generic_permission(&init_user_ns, inode, mask);
        spin_unlock(&inode->i_lock);
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
 
        return ret;
 }

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index f2f909d..cfa7971 100644 (file)
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -236,6 +236,7 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
 {
        struct kernfs_super_info *info = kernfs_info(sb);
+       struct kernfs_root *kf_root = kfc->root;
        struct inode *inode;
        struct dentry *root;
 
@@ -255,9 +256,9 @@ static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *k
        sb->s_shrink.seeks = 0;
 
        /* get root inode, initialize and unlock it */
-       down_read(&kernfs_rwsem);
+       down_read(&kf_root->kernfs_rwsem);
        inode = kernfs_get_inode(sb, info->root->kn);
-       up_read(&kernfs_rwsem);
+       up_read(&kf_root->kernfs_rwsem);
        if (!inode) {
                pr_debug("kernfs: could not get root inode\n");
                return -ENOMEM;
@@ -334,6 +335,7 @@ int kernfs_get_tree(struct fs_context *fc)
 
        if (!sb->s_root) {
                struct kernfs_super_info *info = kernfs_info(sb);
+               struct kernfs_root *root = kfc->root;
 
                kfc->new_sb_created = true;
 
@@ -344,9 +346,9 @@ int kernfs_get_tree(struct fs_context *fc)
                }
                sb->s_flags |= SB_ACTIVE;
 
-               down_write(&kernfs_rwsem);
+               down_write(&root->kernfs_rwsem);
                list_add(&info->node, &info->root->supers);
-               up_write(&kernfs_rwsem);
+               up_write(&root->kernfs_rwsem);
        }
 
        fc->root = dget(sb->s_root);
@@ -371,10 +373,11 @@ void kernfs_free_fs_context(struct fs_context *fc)
 void kernfs_kill_sb(struct super_block *sb)
 {
        struct kernfs_super_info *info = kernfs_info(sb);
+       struct kernfs_root *root = info->root;
 
-       down_write(&kernfs_rwsem);
+       down_write(&root->kernfs_rwsem);
        list_del(&info->node);
-       up_write(&kernfs_rwsem);
+       up_write(&root->kernfs_rwsem);
 
        /*
         * Remove the superblock from fs_supers/s_instances

diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c
index 19a6c71..0ab1382 100644 (file)
--- a/fs/kernfs/symlink.c
+++ b/fs/kernfs/symlink.c
@@ -113,11 +113,12 @@ static int kernfs_getlink(struct inode *inode, char *path)
        struct kernfs_node *kn = inode->i_private;
        struct kernfs_node *parent = kn->parent;
        struct kernfs_node *target = kn->symlink.target_kn;
+       struct kernfs_root *root = kernfs_root(parent);
        int error;
 
-       down_read(&kernfs_rwsem);
+       down_read(&root->kernfs_rwsem);
        error = kernfs_get_target_path(parent, target, path);
-       up_read(&kernfs_rwsem);
+       up_read(&root->kernfs_rwsem);
 
        return error;
 }

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 3ccce6f..9f65098 100644 (file)
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -16,6 +16,7 @@
 #include <linux/atomic.h>
 #include <linux/uidgid.h>
 #include <linux/wait.h>
+#include <linux/rwsem.h>
 
 struct file;
 struct dentry;
@@ -197,6 +198,7 @@ struct kernfs_root {
        struct list_head        supers;
 
        wait_queue_head_t       deactivate_waitq;
+       struct rw_semaphore     kernfs_rwsem;
 };
 
 struct kernfs_open_file {