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Subject[PATCH] rculist: Add build check for single optional list argument
Date
In a previous patch series [1], we added an optional lockdep expression
argument to list_for_each_entry_rcu() and the hlist equivalent. This
also meant more than one optional argument can be passed to them with
that error going unnoticed. To fix this, let us force a compiler error
more than one optional argument is passed.

[1] https://lore.kernel.org/patchwork/project/lkml/list/?series=402150

Suggested-by: Paul McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
include/linux/rculist.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 1048160625bb..86659f6d72dc 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -44,14 +44,18 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
* 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, ...) \
+#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, ...) ({})
+#define __list_check_rcu(dummy, cond, extra...) \
+ ({ check_arg_count_one(extra); })
#endif

/*
--
2.22.0.510.g264f2c817a-goog
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