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namei.c: split unlazy_walk()

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In all but one case, the last two arguments are NULL and 0 resp.;
almost everyone just wants to switch nameidata to non-RCU mode.
The only exception is lookup_fast(), where we have a child dentry
we want to legitimize as well.  Split these two cases.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2017-01-09 22:29:15 -05:00
parent a89f833737
commit 4675ac39b5
1 changed files with 66 additions and 39 deletions
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105
fs/namei.c
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@ -672,52 +672,83 @@ static bool legitimize_links(struct nameidata *nd)
/**
* unlazy_walk - try to switch to ref-walk mode.
* @nd: nameidata pathwalk data
* @dentry: child of nd->path.dentry or NULL
* @seq: seq number to check dentry against
* Returns: 0 on success, -ECHILD on failure
*
* 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.
* unlazy_walk attempts to legitimize the current nd->path and nd->root
* for ref-walk mode.
* 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)
static int unlazy_walk(struct nameidata *nd)
{
struct dentry *parent = nd->path.dentry;
BUG_ON(!(nd->flags & LOOKUP_RCU));
nd->flags &= ~LOOKUP_RCU;
if (unlikely(!legitimize_links(nd)))
goto out2;
if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
goto out1;
if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq)))
goto out;
}
rcu_read_unlock();
BUG_ON(nd->inode != parent->d_inode);
return 0;
out2:
nd->path.mnt = NULL;
nd->path.dentry = NULL;
out1:
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
out:
rcu_read_unlock();
return -ECHILD;
}
/**
* unlazy_child - try to switch to ref-walk mode.
* @nd: nameidata pathwalk data
* @dentry: child of nd->path.dentry
* @seq: seq number to check dentry against
* Returns: 0 on success, -ECHILD on failure
*
* unlazy_child 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. Must be called from rcu-walk context.
* Nothing should touch nameidata between unlazy_child() failure and
* terminate_walk().
*/
static int unlazy_child(struct nameidata *nd, struct dentry *dentry, unsigned seq)
{
BUG_ON(!(nd->flags & LOOKUP_RCU));
nd->flags &= ~LOOKUP_RCU;
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)))
if (unlikely(!lockref_get_not_dead(&nd->path.dentry->d_lockref)))
goto out1;
/*
* For a negative lookup, the lookup sequence point is the parents
* sequence point, and it only needs to revalidate the parent dentry.
*
* For a positive lookup, we need to move both the parent and the
* dentry from the RCU domain to be properly refcounted. And the
* sequence number in the dentry validates *both* dentry counters,
* since we checked the sequence number of the parent after we got
* the child sequence number. So we know the parent must still
* be valid if the child sequence number is still valid.
* We need to move both the parent and the dentry from the RCU domain
* to be properly refcounted. And the sequence number in the dentry
* validates *both* dentry counters, since we checked the sequence
* number of the parent after we got the child sequence number. So we
* know the parent must still be valid if the child sequence number is
*/
if (!dentry) {
if (read_seqcount_retry(&parent->d_seq, nd->seq))
goto out;
BUG_ON(nd->inode != parent->d_inode);
} else {
if (!lockref_get_not_dead(&dentry->d_lockref))
goto out;
if (read_seqcount_retry(&dentry->d_seq, seq))
goto drop_dentry;
if (unlikely(!lockref_get_not_dead(&dentry->d_lockref)))
goto out;
if (unlikely(read_seqcount_retry(&dentry->d_seq, seq))) {
rcu_read_unlock();
dput(dentry);
goto drop_root_mnt;
}
/*
* Sequence counts matched. Now make sure that the root is
* still valid and get it if required.
@ -733,10 +764,6 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq
rcu_read_unlock();
return 0;
drop_dentry:
rcu_read_unlock();
dput(dentry);
goto drop_root_mnt;
out2:
nd->path.mnt = NULL;
out1:
@ -775,7 +802,7 @@ static int complete_walk(struct nameidata *nd)
if (nd->flags & LOOKUP_RCU) {
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
if (unlikely(unlazy_walk(nd, NULL, 0)))
if (unlikely(unlazy_walk(nd)))
return -ECHILD;
}
@ -1001,7 +1028,7 @@ const char *get_link(struct nameidata *nd)
touch_atime(&last->link);
cond_resched();
} else if (atime_needs_update_rcu(&last->link, inode)) {
if (unlikely(unlazy_walk(nd, NULL, 0)))
if (unlikely(unlazy_walk(nd)))
return ERR_PTR(-ECHILD);
touch_atime(&last->link);
}
@ -1020,7 +1047,7 @@ const char *get_link(struct nameidata *nd)
if (nd->flags & LOOKUP_RCU) {
res = get(NULL, inode, &last->done);
if (res == ERR_PTR(-ECHILD)) {
if (unlikely(unlazy_walk(nd, NULL, 0)))
if (unlikely(unlazy_walk(nd)))
return ERR_PTR(-ECHILD);
res = get(dentry, inode, &last->done);
}
@ -1529,7 +1556,7 @@ static int lookup_fast(struct nameidata *nd,
bool negative;
dentry = __d_lookup_rcu(parent, &nd->last, &seq);
if (unlikely(!dentry)) {
if (unlazy_walk(nd, NULL, 0))
if (unlazy_walk(nd))
return -ECHILD;
return 0;
}
@ -1567,7 +1594,7 @@ static int lookup_fast(struct nameidata *nd,
if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
return 1;
}
if (unlazy_walk(nd, dentry, seq))
if (unlazy_child(nd, dentry, seq))
return -ECHILD;
if (unlikely(status == -ECHILD))
/* we'd been told to redo it in non-rcu mode */
@ -1646,7 +1673,7 @@ static inline int may_lookup(struct nameidata *nd)
int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
if (err != -ECHILD)
return err;
if (unlazy_walk(nd, NULL, 0))
if (unlazy_walk(nd))
return -ECHILD;
}
return inode_permission(nd->inode, MAY_EXEC);
@ -1690,7 +1717,7 @@ static int pick_link(struct nameidata *nd, struct path *link,
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
rcu_read_unlock();
} else if (likely(unlazy_walk(nd, NULL, 0)) == 0)
} else if (likely(unlazy_walk(nd)) == 0)
error = nd_alloc_stack(nd);
}
if (error) {
@ -2108,7 +2135,7 @@ OK:
}
if (unlikely(!d_can_lookup(nd->path.dentry))) {
if (nd->flags & LOOKUP_RCU) {
if (unlazy_walk(nd, NULL, 0))
if (unlazy_walk(nd))
return -ECHILD;
}
return -ENOTDIR;
@ -2565,7 +2592,7 @@ mountpoint_last(struct nameidata *nd)
/* If we're in rcuwalk, drop out of it to handle last component */
if (nd->flags & LOOKUP_RCU) {
if (unlazy_walk(nd, NULL, 0))
if (unlazy_walk(nd))
return -ECHILD;
}