From d25ad38eafbcc11ec1807eb33e5c5ad804ce1a58 Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Tue, 14 May 2024 10:46:10 +0200
Subject: [PATCH] RCU Unwinder refactored from route table to a separate
 structure

---
 conf/conf.c     |  1 -
 lib/birdlib.h   |  1 +
 lib/locking.h   | 40 ++++++++++++++++++++++++++++++++++++++++
 nest/rt-table.c | 29 +++++++++--------------------
 proto/bgp/bgp.h |  1 -
 5 files changed, 50 insertions(+), 22 deletions(-)

diff --git a/conf/conf.c b/conf/conf.c
index 8fdf4b37..90dbb444 100644
--- a/conf/conf.c
+++ b/conf/conf.c
@@ -40,7 +40,6 @@
  * text to make the parser recognize only the rules corresponding to CLI commands.
  */
 
-#include <setjmp.h>
 #include <stdarg.h>
 
 #undef LOCAL_DEBUG
diff --git a/lib/birdlib.h b/lib/birdlib.h
index 96c9326b..9a1a3e6d 100644
--- a/lib/birdlib.h
+++ b/lib/birdlib.h
@@ -10,6 +10,7 @@
 #define _BIRD_BIRDLIB_H_
 
 #include <stddef.h>
+#include <setjmp.h>
 
 #include "sysdep/config.h"
 #include "lib/alloca.h"
diff --git a/lib/locking.h b/lib/locking.h
index e79730f1..56ed2651 100644
--- a/lib/locking.h
+++ b/lib/locking.h
@@ -10,6 +10,7 @@
 #define _BIRD_LOCKING_H_
 
 #include "lib/macro.h"
+#include "lib/rcu.h"
 
 struct domain_generic;
 struct pool;
@@ -337,4 +338,43 @@ static inline void locking_unwind(struct lock_order *desired)
 #define LOBJ_PRIV(_obj, _level) \
   ({ ASSERT_DIE(DOMAIN_IS_LOCKED(_level, (_obj)->lock)); &(_obj)->priv; })
 
+
+/*
+ * RCU retry unwinder
+ *
+ * Start a retriable operation with RCU_ANCHOR() and pass the _i object along
+ * with the code which may then call RCU_RETRY() to return back to RCU_ANCHOR
+ * and try again.
+ */
+
+struct rcu_unwinder {
+  struct lock_order locking_stack;
+  u64 retry;
+  jmp_buf buf;
+};
+
+static inline void _rcu_unwinder_unlock_(struct rcu_unwinder *o UNUSED)
+{
+  rcu_read_unlock();
+}
+
+#define RCU_UNWIND_WARN	4096
+
+#define RCU_ANCHOR(_i)	\
+  CLEANUP(_rcu_unwinder_unlock_) struct rcu_unwinder _s##_i = {};	\
+  struct rcu_unwinder *_i = &_s##_i;					\
+  if (setjmp(_i->buf)) {						\
+    rcu_read_unlock();							\
+    locking_unwind(&_i->locking_stack);					\
+    birdloop_yield();							\
+    if (!(++_i->retry % RCU_UNWIND_WARN))				\
+      log(L_WARN "Suspiciously many RCU_ANCHORs retried (%lu)"		\
+	 " at %s:%d", _i->retry, __FILE__, __LINE__);			\
+  }									\
+  _i->locking_stack = locking_stack;					\
+  rcu_read_lock();							\
+
+#define RCU_RETRY(_i) do { if (_i) longjmp(_i->buf, 1); else bug("No rcu retry allowed here"); } while (0)
+
+#define RCU_WONT_RETRY	((struct rcu_unwinder *) NULL)
 #endif
diff --git a/nest/rt-table.c b/nest/rt-table.c
index dd8ee7bc..6fb6eed7 100644
--- a/nest/rt-table.c
+++ b/nest/rt-table.c
@@ -215,9 +215,7 @@ static inline rtable *rt_pub_to_pub(rtable *tab) { return tab; }
  */
 struct rtable_reading {
   rtable *t;
-  struct lock_order locking_stack;
-  u64 retry;
-  jmp_buf buf;
+  struct rcu_unwinder *u;
 };
 
 static inline void _rt_rcu_unlock_(struct rtable_reading *o)
@@ -226,25 +224,17 @@ static inline void _rt_rcu_unlock_(struct rtable_reading *o)
     rcu_read_unlock();
 }
 
-#define RT_READ(_o, _i) \
-  CLEANUP(_rt_rcu_unlock_) struct rtable_reading _s##_i = { .t = _o };	\
-  struct rtable_reading *_i = &_s##_i;					\
-  if (setjmp(_i->buf)) {						\
-    rcu_read_unlock();							\
-    locking_unwind(&_i->locking_stack);					\
-    birdloop_yield();							\
-    if (!(++_i->retry % NET_GET_BLOCK_WARN))				\
-      log(L_WARN "Suspiciously many RT_READs retried (%lu) in table %s"	\
-	 " at %s:%d", _i->retry, _i->t->name, __FILE__, __LINE__);	\
-  }									\
-  _i->locking_stack = locking_stack;					\
-  rcu_read_lock();							\
+#define RT_READ_ANCHORED(_o, _i, _u)  \
+  struct rtable_reading _s##_i = { .t = _o, .u = _u, }, *_i = &_s##_i;
 
-#define RT_READ_RETRY(tr) do { if (RT_IS_LOCKED(tr->t)) bug("No obsolete route allowed here"); else longjmp(tr->buf, 1); } while (0)
+#define RT_READ(_o, _i) RCU_ANCHOR(_u##_i); RT_READ_ANCHORED(_o, _i, _u##_i);
+
+#define RT_READ_RETRY(tr) RCU_RETRY(tr->u)
 
 #define RT_READ_LOCKED(_o, _i) \
-  struct rtable_reading _s##_i = { .t = RT_PUB(_o) },	\
-  *_i = ({ ASSERT_DIE(RT_IS_LOCKED(_o)); &_s##_i; });	\
+  ASSERT_DIE(RT_IS_LOCKED(_o));	\
+  struct rtable_reading _s##_i = { .t = RT_PUB(_o), .u = RCU_WONT_RETRY, }, *_i = &_s##_i;
+
 
 #define RTE_IS_OBSOLETE(s)  ((s)->rte.flags & REF_OBSOLETE)
 #define RTE_OBSOLETE_CHECK(tr, _s) ({	\
@@ -253,7 +243,6 @@ static inline void _rt_rcu_unlock_(struct rtable_reading *o)
       RT_READ_RETRY(tr);		\
     s; })
 
-#define NET_GET_BLOCK_WARN  16384
 #define NET_READ_WALK_ROUTES(tr, n, ptr, r)						\
   for (struct rte_storage *r, * _Atomic *ptr = &(n)->routes;				\
       r = RTE_OBSOLETE_CHECK(tr, atomic_load_explicit(ptr, memory_order_acquire));	\
diff --git a/proto/bgp/bgp.h b/proto/bgp/bgp.h
index 913d8cfb..3d234fa2 100644
--- a/proto/bgp/bgp.h
+++ b/proto/bgp/bgp.h
@@ -12,7 +12,6 @@
 #define _BIRD_BGP_H_
 
 #include <stdint.h>
-#include <setjmp.h>
 #include "nest/bird.h"
 #include "nest/route.h"
 #include "nest/bfd.h"