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namei: make unlazy_walk and terminate_walk handle nd->stack, add unlazy_link 

We are almost done - primitives for leaving RCU mode are aware of nd->stack
now, a new primitive for going to non-RCU mode when we have a symlink on hands
added.

The thing we are heavily relying upon is that *any* unlazy failure will be
shortly followed by terminate_walk(), with no access to nameidata in between.
So it's enough to leave the things in a state terminate_walk() would cope with.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2015-05-09 12:55:43 -04:00
parent 0450b2d120
commit 7973387a2f
1 changed files with 100 additions and 38 deletions
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138
fs/namei.c
View File

@ -554,6 +554,68 @@ static inline int nd_alloc_stack(struct nameidata *nd)
return __nd_alloc_stack(nd);
}
static void drop_links(struct nameidata *nd)
{
int i = nd->depth;
while (i--) {
struct saved *last = nd->stack + i;
struct inode *inode = last->inode;
if (last->cookie && inode->i_op->put_link) {
inode->i_op->put_link(inode, last->cookie);
last->cookie = NULL;
}
}
}
static void terminate_walk(struct nameidata *nd)
{
drop_links(nd);
if (!(nd->flags & LOOKUP_RCU)) {
int i;
path_put(&nd->path);
for (i = 0; i < nd->depth; i++)
path_put(&nd->stack[i].link);
} else {
nd->flags &= ~LOOKUP_RCU;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
rcu_read_unlock();
}
nd->depth = 0;
}
/* path_put is needed afterwards regardless of success or failure */
static bool legitimize_path(struct nameidata *nd,
struct path *path, unsigned seq)
{
int res = __legitimize_mnt(path->mnt, nd->m_seq);
if (unlikely(res)) {
if (res > 0)
path->mnt = NULL;
path->dentry = NULL;
return false;
}
if (unlikely(!lockref_get_not_dead(&path->dentry->d_lockref))) {
path->dentry = NULL;
return false;
}
return !read_seqcount_retry(&path->dentry->d_seq, seq);
}
static bool legitimize_links(struct nameidata *nd)
{
int i;
for (i = 0; i < nd->depth; i++) {
struct saved *last = nd->stack + i;
if (unlikely(!legitimize_path(nd, &last->link, last->seq))) {
drop_links(nd);
nd->depth = i + 1;
return false;
}
}
return true;
}
/*
* Path walking has 2 modes, rcu-walk and ref-walk (see
* Documentation/filesystems/path-lookup.txt). In situations when we can't
@ -575,6 +637,8 @@ static inline int nd_alloc_stack(struct nameidata *nd)
* unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
* for ref-walk mode. @dentry must be a path found by a do_lookup call on
* @nd or NULL. Must be called from rcu-walk context.
* Nothing should touch nameidata between unlazy_walk() failure and
* terminate_walk().
*/
static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq)
{
@ -583,22 +647,13 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq
BUG_ON(!(nd->flags & LOOKUP_RCU));
/*
* After legitimizing the bastards, terminate_walk()
* will do the right thing for non-RCU mode, and all our
* subsequent exit cases should rcu_read_unlock()
* before returning. Do vfsmount first; if dentry
* can't be legitimized, just set nd->path.dentry to NULL
* and rely on dput(NULL) being a no-op.
*/
if (!legitimize_mnt(nd->path.mnt, nd->m_seq))
return -ECHILD;
nd->flags &= ~LOOKUP_RCU;
if (!lockref_get_not_dead(&parent->d_lockref)) {
nd->path.dentry = NULL;
goto out;
}
if (unlikely(!legitimize_links(nd)))
goto out2;
if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))
goto out2;
if (unlikely(!lockref_get_not_dead(&parent->d_lockref)))
goto out1;
/*
* For a negative lookup, the lookup sequence point is the parents
@ -628,8 +683,10 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq
*/
if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
spin_lock(&fs->lock);
if (nd->root.mnt != fs->root.mnt || nd->root.dentry != fs->root.dentry)
goto unlock_and_drop_dentry;
if (unlikely(!path_equal(&nd->root, &fs->root))) {
spin_unlock(&fs->lock);
goto drop_dentry;
}
path_get(&nd->root);
spin_unlock(&fs->lock);
}
@ -637,12 +694,14 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq
rcu_read_unlock();
return 0;
unlock_and_drop_dentry:
spin_unlock(&fs->lock);
drop_dentry:
rcu_read_unlock();
dput(dentry);
goto drop_root_mnt;
out2:
nd->path.mnt = NULL;
out1:
nd->path.dentry = NULL;
out:
rcu_read_unlock();
drop_root_mnt:
@ -651,6 +710,24 @@ drop_root_mnt:
return -ECHILD;
}
static int unlazy_link(struct nameidata *nd, struct path *link, unsigned seq)
{
if (unlikely(!legitimize_path(nd, link, seq))) {
drop_links(nd);
nd->depth = 0;
nd->flags &= ~LOOKUP_RCU;
nd->path.mnt = NULL;
nd->path.dentry = NULL;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
rcu_read_unlock();
} else if (likely(unlazy_walk(nd, NULL, 0)) == 0) {
return 0;
}
path_put(link);
return -ECHILD;
}
static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
{
return dentry->d_op->d_revalidate(dentry, flags);
@ -1537,20 +1614,6 @@ static inline int handle_dots(struct nameidata *nd, int type)
return 0;
}
static void terminate_walk(struct nameidata *nd)
{
if (!(nd->flags & LOOKUP_RCU)) {
path_put(&nd->path);
} else {
nd->flags &= ~LOOKUP_RCU;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
rcu_read_unlock();
}
while (unlikely(nd->depth))
put_link(nd);
}
static int pick_link(struct nameidata *nd, struct path *link,
struct inode *inode, unsigned seq)
{
@ -1561,13 +1624,12 @@ static int pick_link(struct nameidata *nd, struct path *link,
return -ELOOP;
}
if (nd->flags & LOOKUP_RCU) {
if (unlikely(nd->path.mnt != link->mnt ||
unlazy_walk(nd, link->dentry, seq))) {
if (unlikely(unlazy_link(nd, link, seq)))
return -ECHILD;
}
} else {
if (link->mnt == nd->path.mnt)
mntget(link->mnt);
}
if (link->mnt == nd->path.mnt)
mntget(link->mnt);
error = nd_alloc_stack(nd);
if (unlikely(error)) {
path_put(link);