VFS: Impose ordering on accesses of d_inode and d_flags
Impose ordering on accesses of d_inode and d_flags to avoid the need to do
this:
if (!dentry->d_inode || d_is_negative(dentry)) {
when this:
if (d_is_negative(dentry)) {
should suffice.
This check is especially problematic if a dentry can have its type field set
to something other than DENTRY_MISS_TYPE when d_inode is NULL (as in
unionmount).
What we really need to do is stick a write barrier between setting d_inode and
setting d_flags and a read barrier between reading d_flags and reading
d_inode.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index e83768e..df334cb 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -404,26 +404,11 @@
/*
* Directory cache entry type accessor functions.
*/
-static inline void __d_set_type(struct dentry *dentry, unsigned type)
-{
- dentry->d_flags = (dentry->d_flags & ~DCACHE_ENTRY_TYPE) | type;
-}
-
-static inline void __d_clear_type(struct dentry *dentry)
-{
- __d_set_type(dentry, DCACHE_MISS_TYPE);
-}
-
-static inline void d_set_type(struct dentry *dentry, unsigned type)
-{
- spin_lock(&dentry->d_lock);
- __d_set_type(dentry, type);
- spin_unlock(&dentry->d_lock);
-}
-
static inline unsigned __d_entry_type(const struct dentry *dentry)
{
- return dentry->d_flags & DCACHE_ENTRY_TYPE;
+ unsigned type = READ_ONCE(dentry->d_flags);
+ smp_rmb();
+ return type & DCACHE_ENTRY_TYPE;
}
static inline bool d_is_miss(const struct dentry *dentry)