Existing kernfs_xattr_get() locks iattr_mutex, so it cannot be used in
RCU critical sections. Introduce __kernfs_xattr_get(), which reads xattr
under RCU read lock. This can be used by BPF programs to access cgroupfs
xattrs.
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
fs/kernfs/inode.c | 14 ++++++++++++++
include/linux/kernfs.h | 2 ++
2 files changed, 16 insertions(+)
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index b83054da68b3..0ca231d2012c 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -302,6 +302,20 @@ int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
return simple_xattr_get(&attrs->xattrs, name, value, size);
}
+int __kernfs_xattr_get(struct kernfs_node *kn, const char *name,
+ void *value, size_t size)
+{
+ struct kernfs_iattrs *attrs;
+
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
+ attrs = rcu_dereference(kn->iattr);
+ if (!attrs)
+ return -ENODATA;
+
+ return simple_xattr_get(&attrs->xattrs, name, value, size);
+}
+
int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
const void *value, size_t size, int flags)
{
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index b5a5f32fdfd1..8536ffc5c9f1 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -456,6 +456,8 @@ void kernfs_notify(struct kernfs_node *kn);
int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
void *value, size_t size);
+int __kernfs_xattr_get(struct kernfs_node *kn, const char *name,
+ void *value, size_t size);
int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
const void *value, size_t size, int flags);
--
2.47.1
