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![Minchan Kim](/assets/img/avatar_default.png)
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>
400 lines
9.7 KiB
C
400 lines
9.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* fs/kernfs/mount.c - kernfs mount implementation
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*
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* Copyright (c) 2001-3 Patrick Mochel
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* Copyright (c) 2007 SUSE Linux Products GmbH
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* Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
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*/
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#include <linux/fs.h>
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#include <linux/mount.h>
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#include <linux/init.h>
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#include <linux/magic.h>
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#include <linux/slab.h>
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#include <linux/pagemap.h>
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#include <linux/namei.h>
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#include <linux/seq_file.h>
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#include <linux/exportfs.h>
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#include "kernfs-internal.h"
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struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
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static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
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{
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struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
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struct kernfs_syscall_ops *scops = root->syscall_ops;
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if (scops && scops->show_options)
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return scops->show_options(sf, root);
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return 0;
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}
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static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
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{
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struct kernfs_node *node = kernfs_dentry_node(dentry);
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struct kernfs_root *root = kernfs_root(node);
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struct kernfs_syscall_ops *scops = root->syscall_ops;
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if (scops && scops->show_path)
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return scops->show_path(sf, node, root);
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seq_dentry(sf, dentry, " \t\n\\");
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return 0;
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}
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const struct super_operations kernfs_sops = {
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.statfs = simple_statfs,
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.drop_inode = generic_delete_inode,
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.evict_inode = kernfs_evict_inode,
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.show_options = kernfs_sop_show_options,
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.show_path = kernfs_sop_show_path,
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};
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static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
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struct inode *parent)
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{
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struct kernfs_node *kn = inode->i_private;
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if (*max_len < 2) {
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*max_len = 2;
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return FILEID_INVALID;
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}
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*max_len = 2;
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*(u64 *)fh = kn->id;
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return FILEID_KERNFS;
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}
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static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
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struct fid *fid, int fh_len,
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int fh_type, bool get_parent)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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struct kernfs_node *kn;
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struct inode *inode;
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u64 id;
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if (fh_len < 2)
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return NULL;
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switch (fh_type) {
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case FILEID_KERNFS:
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id = *(u64 *)fid;
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break;
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case FILEID_INO32_GEN:
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case FILEID_INO32_GEN_PARENT:
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/*
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* blk_log_action() exposes "LOW32,HIGH32" pair without
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* type and userland can call us with generic fid
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* constructed from them. Combine it back to ID. See
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* blk_log_action().
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*/
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id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
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break;
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default:
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return NULL;
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}
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kn = kernfs_find_and_get_node_by_id(info->root, id);
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if (!kn)
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return ERR_PTR(-ESTALE);
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if (get_parent) {
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struct kernfs_node *parent;
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parent = kernfs_get_parent(kn);
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kernfs_put(kn);
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kn = parent;
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if (!kn)
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return ERR_PTR(-ESTALE);
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}
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inode = kernfs_get_inode(sb, kn);
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kernfs_put(kn);
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if (!inode)
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return ERR_PTR(-ESTALE);
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return d_obtain_alias(inode);
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}
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static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
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struct fid *fid, int fh_len,
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int fh_type)
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{
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return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
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}
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static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
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struct fid *fid, int fh_len,
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int fh_type)
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{
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return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
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}
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static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
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{
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struct kernfs_node *kn = kernfs_dentry_node(child);
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return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
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}
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static const struct export_operations kernfs_export_ops = {
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.encode_fh = kernfs_encode_fh,
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.fh_to_dentry = kernfs_fh_to_dentry,
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.fh_to_parent = kernfs_fh_to_parent,
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.get_parent = kernfs_get_parent_dentry,
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};
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/**
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* kernfs_root_from_sb - determine kernfs_root associated with a super_block
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* @sb: the super_block in question
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*
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* Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
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* %NULL is returned.
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*/
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struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
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{
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if (sb->s_op == &kernfs_sops)
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return kernfs_info(sb)->root;
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return NULL;
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}
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/*
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* find the next ancestor in the path down to @child, where @parent was the
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* ancestor whose descendant we want to find.
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*
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* Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
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* node. If @parent is b, then we return the node for c.
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* Passing in d as @parent is not ok.
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*/
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static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
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struct kernfs_node *parent)
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{
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if (child == parent) {
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pr_crit_once("BUG in find_next_ancestor: called with parent == child");
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return NULL;
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}
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while (child->parent != parent) {
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if (!child->parent)
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return NULL;
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child = child->parent;
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}
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return child;
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}
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/**
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* kernfs_node_dentry - get a dentry for the given kernfs_node
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* @kn: kernfs_node for which a dentry is needed
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* @sb: the kernfs super_block
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*/
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struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
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struct super_block *sb)
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{
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struct dentry *dentry;
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struct kernfs_node *knparent = NULL;
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BUG_ON(sb->s_op != &kernfs_sops);
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dentry = dget(sb->s_root);
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/* Check if this is the root kernfs_node */
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if (!kn->parent)
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return dentry;
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knparent = find_next_ancestor(kn, NULL);
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if (WARN_ON(!knparent)) {
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dput(dentry);
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return ERR_PTR(-EINVAL);
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}
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do {
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struct dentry *dtmp;
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struct kernfs_node *kntmp;
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if (kn == knparent)
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return dentry;
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kntmp = find_next_ancestor(kn, knparent);
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if (WARN_ON(!kntmp)) {
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dput(dentry);
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return ERR_PTR(-EINVAL);
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}
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dtmp = lookup_positive_unlocked(kntmp->name, dentry,
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strlen(kntmp->name));
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dput(dentry);
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if (IS_ERR(dtmp))
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return dtmp;
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knparent = kntmp;
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dentry = dtmp;
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} while (true);
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}
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static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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struct kernfs_root *kf_root = kfc->root;
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struct inode *inode;
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struct dentry *root;
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info->sb = sb;
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/* Userspace would break if executables or devices appear on sysfs */
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sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
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sb->s_blocksize = PAGE_SIZE;
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sb->s_blocksize_bits = PAGE_SHIFT;
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sb->s_magic = kfc->magic;
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sb->s_op = &kernfs_sops;
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sb->s_xattr = kernfs_xattr_handlers;
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if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
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sb->s_export_op = &kernfs_export_ops;
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sb->s_time_gran = 1;
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/* sysfs dentries and inodes don't require IO to create */
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sb->s_shrink.seeks = 0;
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/* get root inode, initialize and unlock it */
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down_read(&kf_root->kernfs_rwsem);
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inode = kernfs_get_inode(sb, info->root->kn);
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up_read(&kf_root->kernfs_rwsem);
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if (!inode) {
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pr_debug("kernfs: could not get root inode\n");
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return -ENOMEM;
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}
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/* instantiate and link root dentry */
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root = d_make_root(inode);
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if (!root) {
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pr_debug("%s: could not get root dentry!\n", __func__);
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return -ENOMEM;
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}
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sb->s_root = root;
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sb->s_d_op = &kernfs_dops;
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return 0;
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}
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static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
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{
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struct kernfs_super_info *sb_info = kernfs_info(sb);
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struct kernfs_super_info *info = fc->s_fs_info;
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return sb_info->root == info->root && sb_info->ns == info->ns;
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}
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static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
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{
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struct kernfs_fs_context *kfc = fc->fs_private;
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kfc->ns_tag = NULL;
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return set_anon_super_fc(sb, fc);
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}
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/**
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* kernfs_super_ns - determine the namespace tag of a kernfs super_block
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* @sb: super_block of interest
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*
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* Return the namespace tag associated with kernfs super_block @sb.
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*/
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const void *kernfs_super_ns(struct super_block *sb)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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return info->ns;
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}
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/**
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* kernfs_get_tree - kernfs filesystem access/retrieval helper
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* @fc: The filesystem context.
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*
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* This is to be called from each kernfs user's fs_context->ops->get_tree()
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* implementation, which should set the specified ->@fs_type and ->@flags, and
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* specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
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* respectively.
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*/
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int kernfs_get_tree(struct fs_context *fc)
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{
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struct kernfs_fs_context *kfc = fc->fs_private;
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struct super_block *sb;
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struct kernfs_super_info *info;
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int error;
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info = kzalloc(sizeof(*info), GFP_KERNEL);
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if (!info)
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return -ENOMEM;
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info->root = kfc->root;
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info->ns = kfc->ns_tag;
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INIT_LIST_HEAD(&info->node);
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fc->s_fs_info = info;
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sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
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if (IS_ERR(sb))
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return PTR_ERR(sb);
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if (!sb->s_root) {
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struct kernfs_super_info *info = kernfs_info(sb);
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struct kernfs_root *root = kfc->root;
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kfc->new_sb_created = true;
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error = kernfs_fill_super(sb, kfc);
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if (error) {
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deactivate_locked_super(sb);
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return error;
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}
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sb->s_flags |= SB_ACTIVE;
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down_write(&root->kernfs_rwsem);
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list_add(&info->node, &info->root->supers);
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up_write(&root->kernfs_rwsem);
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}
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fc->root = dget(sb->s_root);
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return 0;
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}
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void kernfs_free_fs_context(struct fs_context *fc)
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{
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/* Note that we don't deal with kfc->ns_tag here. */
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kfree(fc->s_fs_info);
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fc->s_fs_info = NULL;
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}
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/**
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* kernfs_kill_sb - kill_sb for kernfs
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* @sb: super_block being killed
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*
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* This can be used directly for file_system_type->kill_sb(). If a kernfs
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* user needs extra cleanup, it can implement its own kill_sb() and call
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* this function at the end.
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*/
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void kernfs_kill_sb(struct super_block *sb)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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struct kernfs_root *root = info->root;
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down_write(&root->kernfs_rwsem);
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list_del(&info->node);
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up_write(&root->kernfs_rwsem);
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/*
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* Remove the superblock from fs_supers/s_instances
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* so we can't find it, before freeing kernfs_super_info.
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*/
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kill_anon_super(sb);
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kfree(info);
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}
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void __init kernfs_init(void)
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{
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kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
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sizeof(struct kernfs_node),
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0, SLAB_PANIC, NULL);
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/* Creates slab cache for kernfs inode attributes */
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kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
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sizeof(struct kernfs_iattrs),
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0, SLAB_PANIC, NULL);
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}
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