fs: rcu-walk aware d_revalidate method
Require filesystems be aware of .d_revalidate being called in rcu-walk
mode (nd->flags & LOOKUP_RCU). For now do a simple push down, returning
-ECHILD from all implementations.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index bdad641..e90ffe6 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -9,7 +9,7 @@
--------------------------- dentry_operations --------------------------
prototypes:
- int (*d_revalidate)(struct dentry *, int);
+ int (*d_revalidate)(struct dentry *, struct nameidata *);
int (*d_hash)(const struct dentry *, const struct inode *,
struct qstr *);
int (*d_compare)(const struct dentry *, const struct inode *,
@@ -21,14 +21,14 @@
char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
locking rules:
- rename_lock ->d_lock may block
-d_revalidate: no no yes
-d_hash no no no
-d_compare: yes no no
-d_delete: no yes no
-d_release: no no yes
-d_iput: no no yes
-d_dname: no no no
+ rename_lock ->d_lock may block rcu-walk
+d_revalidate: no no yes (ref-walk) maybe
+d_hash no no no maybe
+d_compare: yes no no maybe
+d_delete: no yes no no
+d_release: no no yes no
+d_iput: no no yes no
+d_dname: no no no no
--------------------------- inode_operations ---------------------------
prototypes:
diff --git a/Documentation/filesystems/path-lookup.txt b/Documentation/filesystems/path-lookup.txt
index 09b2878..8789d18 100644
--- a/Documentation/filesystems/path-lookup.txt
+++ b/Documentation/filesystems/path-lookup.txt
@@ -317,11 +317,10 @@
The cases where rcu-walk cannot continue are:
* NULL dentry (ie. any uncached path element)
* parent with d_inode->i_op->permission or ACLs
-* dentries with d_revalidate
* Following links
-In future patches, permission checks and d_revalidate become rcu-walk aware. It
-may be possible eventually to make following links rcu-walk aware.
+In future patches, permission checks become rcu-walk aware. It may be possible
+eventually to make following links rcu-walk aware.
Uncached path elements will always require dropping to ref-walk mode, at the
very least because i_mutex needs to be grabbed, and objects allocated.
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index ccf0ce7..cd9756a 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -360,3 +360,23 @@
INIT_LIST_HEAD(&inode->i_dentry);
must be done in the RCU callback.
+
+--
+[recommended]
+ vfs now tries to do path walking in "rcu-walk mode", which avoids
+atomic operations and scalability hazards on dentries and inodes (see
+Documentation/filesystems/path-walk.txt). d_hash and d_compare changes (above)
+are examples of the changes required to support this. For more complex
+filesystem callbacks, the vfs drops out of rcu-walk mode before the fs call, so
+no changes are required to the filesystem. However, this is costly and loses
+the benefits of rcu-walk mode. We will begin to add filesystem callbacks that
+are rcu-walk aware, shown below. Filesystems should take advantage of this
+where possible.
+
+--
+[mandatory]
+ d_revalidate is a callback that is made on every path element (if
+the filesystem provides it), which requires dropping out of rcu-walk mode. This
+may now be called in rcu-walk mode (nd->flags & LOOKUP_RCU). -ECHILD should be
+returned if the filesystem cannot handle rcu-walk. See
+Documentation/filesystems/vfs.txt for more details.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 69b10ff..c936b49 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -863,6 +863,15 @@
dcache. Most filesystems leave this as NULL, because all their
dentries in the dcache are valid
+ d_revalidate may be called in rcu-walk mode (nd->flags & LOOKUP_RCU).
+ If in rcu-walk mode, the filesystem must revalidate the dentry without
+ blocking or storing to the dentry, d_parent and d_inode should not be
+ used without care (because they can go NULL), instead nd->inode should
+ be used.
+
+ If a situation is encountered that rcu-walk cannot handle, return
+ -ECHILD and it will be called again in ref-walk mode.
+
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. The inode is the dentry's inode.