linux-kernel - [PATCH rcu 09/19] srcu: Use export for srcu_struct defined by DEFINE_STATIC

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Message-Id: <20220204233902.1902-9-paulmck@kernel.org>
Date:   Fri,  4 Feb 2022 15:38:52 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, Alexander Aring <aahringo@...hat.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 09/19] srcu: Use export for srcu_struct defined by DEFINE_STATIC_SRCU()

From: Alexander Aring <aahringo@...hat.com>

If an srcu_struct structure defined by tree SRCU's DEFINE_STATIC_SRCU()
is used by a module, sparse will give the following diagnostic:

sparse: symbol '__srcu_struct_nodes_srcu' was not declared. Should it be static?

The problem is that a within-module DEFINE_STATIC_SRCU() must define
a non-static srcu_struct because it is exported by referencing it in a
special '__section("___srcu_struct_ptrs")'.  This reference is needed
so that module load and unloading can invoke init_srcu_struct() and
cleanup_srcu_struct(), respectively.  Unfortunately, sparse is unaware of
'__section("___srcu_struct_ptrs")', resulting in the above false-positive
diagnostic.  To avoid this false positive, this commit therefore creates
a prototype of the srcu_struct with an "extern" keyword.

Signed-off-by: Alexander Aring <aahringo@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 include/linux/srcutree.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 8501b6b459411..44e998643f483 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -131,6 +131,7 @@ struct srcu_struct {
 #ifdef MODULE
 # define __DEFINE_SRCU(name, is_static)					\
 	is_static struct srcu_struct name;				\
+	extern struct srcu_struct * const __srcu_struct_##name;		\
 	struct srcu_struct * const __srcu_struct_##name			\
 		__section("___srcu_struct_ptrs") = &name
 #else
-- 
2.31.1.189.g2e36527f23