fs: change d_hash for rcu-walk

Change d_hash so it may be called from lock-free RCU lookups. See similar
patch for d_compare for details.

For in-tree filesystems, this is just a mechanical change.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

3 files changed, 16 insertions, 4 deletions

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 9a76f8d8bf95..a15ee207b449 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -10,7 +10,8 @@ be able to use diff(1).
 --------------------------- dentry_operations --------------------------
 prototypes:
         int (*d_revalidate)(struct dentry *, int);
-        int (*d_hash) (struct dentry *, struct qstr *);
+        int (*d_hash)(const struct dentry *, const struct inode *,
+                        struct qstr *);
         int (*d_compare)(const struct dentry *, const struct inode *,
                         const struct dentry *, const struct inode *,
                         unsigned int, const char *, const struct qstr *);
@@ -22,7 +23,7 @@ prototypes:
 locking rules:
                 dcache_lock     rename_lock     ->d_lock        may block
 d_revalidate:   no              no              no              yes
-d_hash          no              no              no              yes
+d_hash          no              no              no              no
 d_compare:      no              yes             no              no 
 d_delete:       yes             no              yes             no
 d_release:      no              no              no              yes
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index d44511e20828..9fd31940a8ef 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -333,3 +333,10 @@ unreferenced dentries, and is now only called when the dentry refcount goes to
         .d_compare() calling convention and locking rules are significantly
 changed. Read updated documentation in Documentation/filesystems/vfs.txt (and
 look at examples of other filesystems) for guidance.
+
+---
+[mandatory]
+
+        .d_hash() calling convention and locking rules are significantly
+changed. Read updated documentation in Documentation/filesystems/vfs.txt (and
+look at examples of other filesystems) for guidance.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 250681b8c7cc..69b10ff5ec81 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -847,7 +847,8 @@ defined:
 
 struct dentry_operations {
         int (*d_revalidate)(struct dentry *, struct nameidata *);
-        int (*d_hash)(struct dentry *, struct qstr *);
+        int (*d_hash)(const struct dentry *, const struct inode *,
+                        struct qstr *);
         int (*d_compare)(const struct dentry *, const struct inode *,
                         const struct dentry *, const struct inode *,
                         unsigned int, const char *, const struct qstr *);
@@ -864,7 +865,10 @@ struct dentry_operations {
 
   d_hash: called when the VFS adds a dentry to the hash table. The first
         dentry passed to d_hash is the parent directory that the name is
-        to be hashed into.
+        to be hashed into. The inode is the dentry's inode.
+
+        Same locking and synchronisation rules as d_compare regarding
+        what is safe to dereference etc.
 
   d_compare: called to compare a dentry name with a given name. The first
         dentry is the parent of the dentry to be compared, the second is