Sometimes we might have a RCU managed credential pointer and don't want
to use locking to handle it. Add a function that will take a reference
to the cred iff the refcount is not already zero. Callers can dereference
the pointer under the rcu_read_lock and use that function to take a
reference only if the cred is not on its way to destruction.
Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
---
include/linux/sunrpc/auth.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index 16bd8f8fef8c..6f36b2bf3e05 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -206,5 +206,23 @@ struct rpc_cred * get_rpccred(struct rpc_cred *cred)
return cred;
}
+/**
+ * get_rpccred_rcu - get a reference to a cred using rcu-protected pointer
+ * @cred: cred of which to take a reference
+ *
+ * In some cases, we may have a pointer to a credential to which we
+ * want to take a reference, but don't already have one. Because these
+ * objects are freed using RCU, we can access the cr_count while its
+ * on its way to destruction and only take a reference if it's not already
+ * zero.
+ */
+static inline struct rpc_cred *
+get_rpccred_rcu(struct rpc_cred *cred)
+{
+ if (atomic_inc_not_zero(&cred->cr_count))
+ return cred;
+ return NULL;
+}
+
#endif /* __KERNEL__ */
#endif /* _LINUX_SUNRPC_AUTH_H */
--
2.5.5
--
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