xattr: add rcu_head and rhash_head to struct simple_xattr

In preparation for converting simple_xattrs from rbtree to rhashtable,
add rhash_head and rcu_head members to struct simple_xattr. The
rhashtable implementation will use rhash_head for hash table linkage
and RCU-based lockless reads, requiring that replaced or removed xattr
entries be freed via call_rcu() rather than immediately.

Add simple_xattr_free_rcu() which schedules RCU-deferred freeing of an
xattr entry.  This will be used by callers of simple_xattr_set() once
they switch to the rhashtable-based xattr store.

No functional changes.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-1-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/xattr.c b/fs/xattr.c
index 3e49e612e1badc0b3a7c5ab1bf92e0559625bc00..9cbb1917bcb20435351067a1263d6f2478225892 100644 (file)
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -1197,6 +1197,29 @@ void simple_xattr_free(struct simple_xattr *xattr)
        kvfree(xattr);
 }
 
+static void simple_xattr_rcu_free(struct rcu_head *head)
+{
+       struct simple_xattr *xattr;
+
+       xattr = container_of(head, struct simple_xattr, rcu);
+       simple_xattr_free(xattr);
+}
+
+/**
+ * simple_xattr_free_rcu - free an xattr object after an RCU grace period
+ * @xattr: the xattr object
+ *
+ * Schedule RCU-deferred freeing of an xattr entry. This is used by
+ * rhashtable-based callers of simple_xattr_set() that replace or remove
+ * an existing entry while concurrent RCU readers may still be accessing
+ * it.
+ */
+void simple_xattr_free_rcu(struct simple_xattr *xattr)
+{
+       if (xattr)
+               call_rcu(&xattr->rcu, simple_xattr_rcu_free);
+}
+
 /**
  * simple_xattr_alloc - allocate new xattr object
  * @value: value of the xattr object

diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index 296b5ee5c979ec58c85e5c2c21d62a602f46119a..fdbd2095414a43d5ad684dd2ea644e5cc72d562a 100644 (file)
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -16,6 +16,7 @@
 #include <linux/types.h>
 #include <linux/spinlock.h>
 #include <linux/mm.h>
+#include <linux/rhashtable-types.h>
 #include <linux/user_namespace.h>
 #include <uapi/linux/xattr.h>
 
@@ -112,6 +113,8 @@ struct simple_xattrs {
 
 struct simple_xattr {
        struct rb_node rb_node;
+       struct rhash_head hash_node;
+       struct rcu_head rcu;
        char *name;
        size_t size;
        char value[] __counted_by(size);
@@ -122,6 +125,7 @@ void simple_xattrs_free(struct simple_xattrs *xattrs, size_t *freed_space);
 size_t simple_xattr_space(const char *name, size_t size);
 struct simple_xattr *simple_xattr_alloc(const void *value, size_t size);
 void simple_xattr_free(struct simple_xattr *xattr);
+void simple_xattr_free_rcu(struct simple_xattr *xattr);
 int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
                     void *buffer, size_t size);
 struct simple_xattr *simple_xattr_set(struct simple_xattrs *xattrs,