[ovs-dev] [PATCH 1/2] compat: rcu: Add support for consolidated-RCU reader checking

[Greg Rose]

From: "Joel Fernandes (Google)" <joel at joelfernandes.org>

Upstream commit:
    commit 28875945ba98d1b47a8a706812b6494d165bb0a0
    Author: Joel Fernandes (Google) <joel at joelfernandes.org>
    Date:   Tue Jul 16 18:12:22 2019 -0400

    rcu: Add support for consolidated-RCU reader checking

    This commit adds RCU-reader checks to list_for_each_entry_rcu() and
    hlist_for_each_entry_rcu().  These checks are optional, and are indicated
    by a lockdep expression passed to a new optional argument to these two
    macros.  If this optional lockdep expression is omitted, these two macros
    act as before, checking for an RCU read-side critical section.

    Signed-off-by: Joel Fernandes (Google) <joel at joelfernandes.org>
    [ paulmck: Update to eliminate return within macro and update comment. ]
    Signed-off-by: Paul E. McKenney <paulmck at linux.ibm.com>

Backport portion of upstream commit for hlist_for_each_entry_rcu() macro
so that it can be used in following bug fix.

Cc: Joel Fernandes (Google) <joel at joelfernandes.org>
Signed-off-by: Greg Rose <gvrose8192 at gmail.com>
---
 datapath/linux/compat/include/linux/rculist.h | 23 +++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/datapath/linux/compat/include/linux/rculist.h b/datapath/linux/compat/include/linux/rculist.h
index 8df8ad8a2..40fd5e171 100644
--- a/datapath/linux/compat/include/linux/rculist.h
+++ b/datapath/linux/compat/include/linux/rculist.h
@@ -9,9 +9,28 @@
 #define hlist_pprev_rcu(node)   (*((struct hlist_node __rcu **)((node)->pprev)))
 #endif
 
+/*
+ * Check during list traversal that we are within an RCU reader
+ */
+
+#define check_arg_count_one(dummy)
+
+#ifdef CONFIG_PROVE_RCU_LIST
+#define __list_check_rcu(dummy, cond, extra...)				\
+	({								\
+	check_arg_count_one(extra);					\
+	RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),		\
+			 "RCU-list traversed in non-reader section!");	\
+	 })
+#else
+#define __list_check_rcu(dummy, cond, extra...)				\
+	({ check_arg_count_one(extra); })
+#endif
+
 #undef hlist_for_each_entry_rcu
-#define hlist_for_each_entry_rcu(pos, head, member)			\
-	for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
+#define hlist_for_each_entry_rcu(pos, head, member, cond...)		\
+	for (__list_check_rcu(dummy, ## cond, 0),			\
+	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
 			typeof(*(pos)), member);			\
 		pos;							\
 		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
-- 
2.17.1