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authorAl Viro <viro@zeniv.linux.org.uk>2019-11-04 22:30:52 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2019-11-15 13:49:04 -0500
commitd41efb522e902364ab09c782d511c1bedc388ddd (patch)
treeb68fc238833ef18e63add150a3217e82f0af450b
parent3e5aeec0e267d4422a4e740ce723549a3098a4d1 (diff)
fs/namei.c: pull positivity check into follow_managed()
There are 4 callers; two proceed to check if result is positive and fail with ENOENT if it isn't; one (in handle_lookup_down()) is guaranteed to yield positive and one (in lookup_fast()) is _preceded_ by positivity check. However, follow_managed() on a negative dentry is a (fairly cheap) no-op on anything other than autofs. And negative autofs dentries are never hashed, so lookup_fast() is not going to run into one of those. Moreover, successful follow_managed() on a _positive_ dentry never yields a negative one (and we significantly rely upon that in callers of lookup_fast()). In other words, we can easily transpose the positivity check and the call of follow_managed() in lookup_fast(). And that allows to fold the positivity check *into* follow_managed(), simplifying life for the code downstream of its calls. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/namei.c34
-rw-r--r--include/linux/dcache.h5
2 files changed, 16 insertions, 23 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 671c3c1a3425..ef55155d152f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1206,25 +1206,25 @@ static int follow_automount(struct path *path, struct nameidata *nd,
* - Flagged as automount point
*
* This may only be called in refwalk mode.
+ * On success path->dentry is known positive.
*
* Serialization is taken care of in namespace.c
*/
static int follow_managed(struct path *path, struct nameidata *nd)
{
struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */
- unsigned managed;
+ unsigned flags;
bool need_mntput = false;
int ret = 0;
/* Given that we're not holding a lock here, we retain the value in a
* local variable for each dentry as we look at it so that we don't see
* the components of that value change under us */
- while (managed = READ_ONCE(path->dentry->d_flags),
- managed &= DCACHE_MANAGED_DENTRY,
- unlikely(managed != 0)) {
+ while (flags = READ_ONCE(path->dentry->d_flags),
+ unlikely(flags & DCACHE_MANAGED_DENTRY)) {
/* Allow the filesystem to manage the transit without i_mutex
* being held. */
- if (managed & DCACHE_MANAGE_TRANSIT) {
+ if (flags & DCACHE_MANAGE_TRANSIT) {
BUG_ON(!path->dentry->d_op);
BUG_ON(!path->dentry->d_op->d_manage);
ret = path->dentry->d_op->d_manage(path, false);
@@ -1233,7 +1233,7 @@ static int follow_managed(struct path *path, struct nameidata *nd)
}
/* Transit to a mounted filesystem. */
- if (managed & DCACHE_MOUNTED) {
+ if (flags & DCACHE_MOUNTED) {
struct vfsmount *mounted = lookup_mnt(path);
if (mounted) {
dput(path->dentry);
@@ -1252,7 +1252,7 @@ static int follow_managed(struct path *path, struct nameidata *nd)
}
/* Handle an automount point */
- if (managed & DCACHE_NEED_AUTOMOUNT) {
+ if (flags & DCACHE_NEED_AUTOMOUNT) {
ret = follow_automount(path, nd, &need_mntput);
if (ret < 0)
break;
@@ -1265,10 +1265,12 @@ static int follow_managed(struct path *path, struct nameidata *nd)
if (need_mntput && path->mnt == mnt)
mntput(path->mnt);
- if (ret == -EISDIR || !ret)
- ret = 1;
if (need_mntput)
nd->flags |= LOOKUP_JUMPED;
+ if (ret == -EISDIR || !ret)
+ ret = 1;
+ if (ret > 0 && unlikely(d_flags_negative(flags)))
+ ret = -ENOENT;
if (unlikely(ret < 0))
path_put_conditional(path, nd);
return ret;
@@ -1617,10 +1619,6 @@ static int lookup_fast(struct nameidata *nd,
dput(dentry);
return status;
}
- if (unlikely(d_is_negative(dentry))) {
- dput(dentry);
- return -ENOENT;
- }
path->mnt = mnt;
path->dentry = dentry;
@@ -1807,11 +1805,6 @@ static int walk_component(struct nameidata *nd, int flags)
if (unlikely(err < 0))
return err;
- if (unlikely(d_is_negative(path.dentry))) {
- path_to_nameidata(&path, nd);
- return -ENOENT;
- }
-
seq = 0; /* we are already out of RCU mode */
inode = d_backing_inode(path.dentry);
}
@@ -3352,11 +3345,6 @@ static int do_last(struct nameidata *nd,
if (unlikely(error < 0))
return error;
- if (unlikely(d_is_negative(path.dentry))) {
- path_to_nameidata(&path, nd);
- return -ENOENT;
- }
-
/*
* create/update audit record if it already exists.
*/
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 10090f11ab95..c1488cc84fd9 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -440,6 +440,11 @@ static inline bool d_is_negative(const struct dentry *dentry)
return d_is_miss(dentry);
}
+static inline bool d_flags_negative(unsigned flags)
+{
+ return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE;
+}
+
static inline bool d_is_positive(const struct dentry *dentry)
{
return !d_is_negative(dentry);