rcu: tiny: Record kvfree_call_rcu() call stack for KASAN

When running KASAN with Tiny RCU (e.g. under ARCH=um, where
a working KASAN patch is now available), we don't get any
information on the original kfree_rcu() (or similar) caller
when a problem is reported, as Tiny RCU doesn't record this.

Add the recording, which required pulling kvfree_call_rcu()
out of line for the KASAN case since the recording function
(kasan_record_aux_stack_noalloc) is neither exported, nor
can we include kasan.h into rcutiny.h.

without KASAN, the patch has no size impact (ARCH=um kernel):
    text       data         bss         dec        hex    filename
 6151515    4423154    33148520    43723189    29b29b5    linux
 6151515    4423154    33148520    43723189    29b29b5    linux + patch

with KASAN, the impact on my build was minimal:
    text       data         bss         dec        hex    filename
13915539    7388050    33282304    54585893    340ea25    linux
13911266    7392114    33282304    54585684    340e954    linux + patch
   -4273      +4064         +-0        -209

Acked-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

2 files changed, 24 insertions, 1 deletions

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 5fed476f977f..d84e13f2c384 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -38,7 +38,7 @@ static inline void synchronize_rcu_expedited(void)
  */
 extern void kvfree(const void *addr);
 
-static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+static inline void __kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
 	if (head) {
 		call_rcu(head, func);
@@ -51,6 +51,15 @@ static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 	kvfree((void *) func);
 }
 
+#ifdef CONFIG_KASAN_GENERIC
+void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
+#else
+static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+{
+	__kvfree_call_rcu(head, func);
+}
+#endif
+
 void rcu_qs(void);
 
 static inline void rcu_softirq_qs(void)
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 340b3f8b090d..58ff3721d975 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -217,6 +217,20 @@ bool poll_state_synchronize_rcu(unsigned long oldstate)
 }
 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
 
+#ifdef CONFIG_KASAN_GENERIC
+void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+{
+	if (head) {
+		void *ptr = (void *) head - (unsigned long) func;
+
+		kasan_record_aux_stack_noalloc(ptr);
+	}
+
+	__kvfree_call_rcu(head, func);
+}
+EXPORT_SYMBOL_GPL(kvfree_call_rcu);
+#endif
+
 void __init rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);