[PATCH] rculist: Add build check for single optional list argument

* [PATCH] rculist: Add build check for single optional list argument
@ 2019-07-16  4:07 Joel Fernandes (Google)
  0 siblings, 0 replies; only message in thread
From: Joel Fernandes (Google) @ 2019-07-16  4:07 UTC (permalink / raw)
  To: linux-kernel
  Cc: Joel Fernandes (Google),
	Paul McKenney, Alexey Kuznetsov, Bjorn Helgaas, Borislav Petkov,
	c0d1n61at3, David S. Miller, edumazet, Greg Kroah-Hartman,
	Hideaki YOSHIFUJI, H. Peter Anvin, Ingo Molnar, Jonathan Corbet,
	Josh Triplett, keescook, kernel-hardening, kernel-team,
	Lai Jiangshan, Len Brown, linux-acpi, linux-doc, linux-pci,
	linux-pm, Mathieu Desnoyers, neilb, netdev, Oleg Nesterov,
	Paul E. McKenney, Pavel Machek, peterz, Rafael J. Wysocki,
	Rasmus Villemoes, rcu, Steven Rostedt, Tejun Heo,
	Thomas Gleixner, will,
	maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)

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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