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Subject[PATCH 5/6] vfs: reorganize do_lookup
Date
From: Miklos Szeredi <mszeredi@suse.cz>

do_lookup's uncached lookup part basically open codes __lookup_hash so use that
instead.

This also eliminates the weird retry loop, that could, in theory, retry the
cached lookup any number of times (very unlikely scenario: needs two parallel
do_lookups and d_revalidate always returning zero).

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
fs/namei.c | 136 +++++++++++++++++++++++++----------------------------------
1 files changed, 58 insertions(+), 78 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 482992e..d500cb0 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1112,6 +1112,46 @@ static struct dentry *d_inode_lookup(struct dentry *parent, struct dentry *dentr
return dentry;
}

+static struct dentry *__lookup_hash(struct qstr *name, struct dentry *base,
+ struct nameidata *nd)
+{
+ struct dentry *dentry;
+
+ dentry = d_lookup(base, name);
+
+ if (dentry && d_need_lookup(dentry)) {
+ /*
+ * __lookup_hash is called with the parent dir's i_mutex already
+ * held, so we are good to go here.
+ */
+ return d_inode_lookup(base, dentry, nd);
+ }
+
+ if (dentry && (dentry->d_flags & DCACHE_OP_REVALIDATE)) {
+ int status = d_revalidate(dentry, nd);
+ if (unlikely(status <= 0)) {
+ /*
+ * The dentry failed validation.
+ * If d_revalidate returned 0 attempt to invalidate
+ * the dentry otherwise d_revalidate is asking us
+ * to return a fail status.
+ */
+ if (status < 0) {
+ dput(dentry);
+ return ERR_PTR(status);
+ } else if (!d_invalidate(dentry)) {
+ dput(dentry);
+ dentry = NULL;
+ }
+ }
+ }
+
+ if (!dentry)
+ dentry = d_alloc_and_lookup(base, name, nd);
+
+ return dentry;
+}
+
/*
* It's more convoluted than I'd like it to be, but... it's still fairly
* small and for now I'd prefer to have fast path as straight as possible.
@@ -1167,37 +1207,12 @@ unlazy:
dentry = __d_lookup(parent, name);
}

- if (dentry && unlikely(d_need_lookup(dentry))) {
- dput(dentry);
- dentry = NULL;
- }
-retry:
- if (unlikely(!dentry)) {
- struct inode *dir = parent->d_inode;
- BUG_ON(nd->inode != dir);
+ if (unlikely(!dentry))
+ goto need_lookup;

- 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;
- } else if (unlikely(d_need_lookup(dentry))) {
- dentry = d_inode_lookup(parent, dentry, 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);
+ if (unlikely(d_need_lookup(dentry))) {
+ dput(dentry);
+ goto need_lookup;
}
if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval)
status = d_revalidate(dentry, nd);
@@ -1208,12 +1223,11 @@ retry:
}
if (!d_invalidate(dentry)) {
dput(dentry);
- dentry = NULL;
- need_reval = 1;
- goto retry;
+ goto need_lookup;
}
}

+success:
path->mnt = mnt;
path->dentry = dentry;
err = follow_managed(path, nd);
@@ -1223,6 +1237,17 @@ retry:
}
*inode = path->dentry->d_inode;
return 0;
+
+need_lookup:
+ BUG_ON(nd->inode != parent->d_inode);
+
+ mutex_lock(&parent->d_inode->i_mutex);
+ dentry = __lookup_hash(name, parent, nd);
+ mutex_unlock(&parent->d_inode->i_mutex);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+
+ goto success;
}

static inline int may_lookup(struct nameidata *nd)
@@ -1725,51 +1750,6 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
return err;
}

-static struct dentry *__lookup_hash(struct qstr *name,
- struct dentry *base, struct nameidata *nd)
-{
- struct dentry *dentry;
-
- /*
- * Don't bother with __d_lookup: callers are for creat as
- * well as unlink, so a lot of the time it would cost
- * a double lookup.
- */
- dentry = d_lookup(base, name);
-
- if (dentry && d_need_lookup(dentry)) {
- /*
- * __lookup_hash is called with the parent dir's i_mutex already
- * held, so we are good to go here.
- */
- return d_inode_lookup(base, dentry, nd);
- }
-
- if (dentry && (dentry->d_flags & DCACHE_OP_REVALIDATE)) {
- int status = d_revalidate(dentry, nd);
- if (unlikely(status <= 0)) {
- /*
- * The dentry failed validation.
- * If d_revalidate returned 0 attempt to invalidate
- * the dentry otherwise d_revalidate is asking us
- * to return a fail status.
- */
- if (status < 0) {
- dput(dentry);
- return ERR_PTR(status);
- } else if (!d_invalidate(dentry)) {
- dput(dentry);
- dentry = NULL;
- }
- }
- }
-
- if (!dentry)
- dentry = d_alloc_and_lookup(base, name, nd);
-
- return dentry;
-}
-
/*
* Restricted form of lookup. Doesn't follow links, single-component only,
* needs parent already locked. Doesn't follow mounts.
--
1.7.7


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