untangle do_lookup()
That thing has devolved into rats nest of gotos; sane use of unlikely()
gets rid of that horror and gives much more readable structure:
* make a fast attempt to find a dentry; false negatives are OK.
In RCU mode if everything went fine, we are done, otherwise just drop
out of RCU. If we'd done (RCU) ->d_revalidate() and it had not refused
outright (i.e. didn't give us -ECHILD), remember its result.
* now we are not in RCU mode and hopefully have a dentry. If we
do not, lock parent, do full d_lookup() and if that has not found anything,
allocate and call ->lookup(). If we'd done that ->lookup(), remember that
dentry is good and we don't need to revalidate it.
* now we have a dentry. If it has ->d_revalidate() and we can't
skip it, call it.
* hopefully dentry is good; if not, either fail (in case of error)
or try to invalidate it. If d_invalidate() has succeeded, drop it and
retry everything as if original attempt had not found a dentry.
* now we can finish it up - deal with mountpoint crossing and
automount.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namei.c b/fs/namei.c
index ca9a06a..0bebd13 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -589,29 +589,6 @@
return dentry;
}
-static inline struct dentry *
-do_revalidate_rcu(struct dentry *dentry, struct nameidata *nd)
-{
- int status = d_revalidate(dentry, nd);
- if (likely(status > 0))
- return dentry;
- if (status == -ECHILD) {
- if (nameidata_dentry_drop_rcu(nd, dentry))
- return ERR_PTR(-ECHILD);
- return do_revalidate(dentry, nd);
- }
- if (status < 0)
- return ERR_PTR(status);
- /* Don't d_invalidate in rcu-walk mode */
- if (nameidata_dentry_drop_rcu(nd, dentry))
- return ERR_PTR(-ECHILD);
- if (!d_invalidate(dentry)) {
- dput(dentry);
- dentry = NULL;
- }
- return dentry;
-}
-
/*
* handle_reval_path - force revalidation of a dentry
*
@@ -1213,7 +1190,8 @@
{
struct vfsmount *mnt = nd->path.mnt;
struct dentry *dentry, *parent = nd->path.dentry;
- struct inode *dir;
+ int need_reval = 1;
+ int status = 1;
int err;
/*
@@ -1223,48 +1201,74 @@
*/
if (nd->flags & LOOKUP_RCU) {
unsigned seq;
-
*inode = nd->inode;
dentry = __d_lookup_rcu(parent, name, &seq, inode);
- if (!dentry) {
- if (nameidata_drop_rcu(nd))
- return -ECHILD;
- goto need_lookup;
- }
+ if (!dentry)
+ goto unlazy;
+
/* Memory barrier in read_seqcount_begin of child is enough */
if (__read_seqcount_retry(&parent->d_seq, nd->seq))
return -ECHILD;
-
nd->seq = seq;
+
if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
- dentry = do_revalidate_rcu(dentry, nd);
- if (!dentry)
- goto need_lookup;
- if (IS_ERR(dentry))
- goto fail;
- if (!(nd->flags & LOOKUP_RCU))
- goto done;
+ status = d_revalidate(dentry, nd);
+ if (unlikely(status <= 0)) {
+ if (status != -ECHILD)
+ need_reval = 0;
+ goto unlazy;
+ }
}
path->mnt = mnt;
path->dentry = dentry;
if (likely(__follow_mount_rcu(nd, path, inode, false)))
return 0;
- if (nameidata_drop_rcu(nd))
- return -ECHILD;
- /* fallthru */
+unlazy:
+ if (dentry) {
+ if (nameidata_dentry_drop_rcu(nd, dentry))
+ return -ECHILD;
+ } else {
+ if (nameidata_drop_rcu(nd))
+ return -ECHILD;
+ }
+ } else {
+ dentry = __d_lookup(parent, name);
}
- dentry = __d_lookup(parent, name);
- if (!dentry)
- goto need_lookup;
-found:
- if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
- dentry = do_revalidate(dentry, nd);
- if (!dentry)
- goto need_lookup;
- if (IS_ERR(dentry))
- goto fail;
+
+retry:
+ if (unlikely(!dentry)) {
+ struct inode *dir = parent->d_inode;
+ BUG_ON(nd->inode != dir);
+
+ mutex_lock(&dir->i_mutex);
+ dentry = d_lookup(parent, name);
+ if (likely(!dentry)) {
+ dentry = d_alloc_and_lookup(parent, name, nd);
+ if (IS_ERR(dentry)) {
+ mutex_unlock(&dir->i_mutex);
+ return PTR_ERR(dentry);
+ }
+ /* known good */
+ need_reval = 0;
+ status = 1;
+ }
+ mutex_unlock(&dir->i_mutex);
}
-done:
+ if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval)
+ status = d_revalidate(dentry, nd);
+ if (unlikely(status <= 0)) {
+ if (status < 0) {
+ dput(dentry);
+ return status;
+ }
+ if (!d_invalidate(dentry)) {
+ dput(dentry);
+ dentry = NULL;
+ need_reval = 1;
+ goto retry;
+ }
+ }
+
path->mnt = mnt;
path->dentry = dentry;
err = follow_managed(path, nd->flags);
@@ -1274,39 +1278,6 @@
}
*inode = path->dentry->d_inode;
return 0;
-
-need_lookup:
- dir = parent->d_inode;
- BUG_ON(nd->inode != dir);
-
- mutex_lock(&dir->i_mutex);
- /*
- * First re-do the cached lookup just in case it was created
- * while we waited for the directory semaphore, or the first
- * lookup failed due to an unrelated rename.
- *
- * This could use version numbering or similar to avoid unnecessary
- * cache lookups, but then we'd have to do the first lookup in the
- * non-racy way. However in the common case here, everything should
- * be hot in cache, so would it be a big win?
- */
- dentry = d_lookup(parent, name);
- if (likely(!dentry)) {
- dentry = d_alloc_and_lookup(parent, name, nd);
- mutex_unlock(&dir->i_mutex);
- if (IS_ERR(dentry))
- goto fail;
- goto done;
- }
- /*
- * Uhhuh! Nasty case: the cache was re-populated while
- * we waited on the semaphore. Need to revalidate.
- */
- mutex_unlock(&dir->i_mutex);
- goto found;
-
-fail:
- return PTR_ERR(dentry);
}
static inline int may_lookup(struct nameidata *nd)