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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-01-08 07:43:50 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-02-23 19:59:55 -0800
commit9de630c4f264dec48e61edd871cb98b8e1b58250 (patch)
treee11bfe739aeb1e90d2a0fb31df4339bf39d2ced2 /include/linux/srcu.h
parent9fc9204ef9fdbe550fd81a554abce2b210e63e49 (diff)
rcu: Document unique-name limitation for DEFINE_STATIC_SRCU()
SRCU uses per-CPU variables, and DEFINE_STATIC_SRCU() uses a static per-CPU variable. However, per-CPU variables have significant restrictions, for example, names of per-CPU variables must be globally unique, even if declared static. These restrictions carry over to DEFINE_STATIC_SRCU(), and this commit therefore documents these restrictions. Reported-by: Stephen Rothwell <sfr@canb.auug.org.au> Reported-by: kbuild test robot <fengguang.wu@intel.com> Suggested-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'include/linux/srcu.h')
-rw-r--r--include/linux/srcu.h19
1 files changed, 17 insertions, 2 deletions
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index f5f80c5643ac..dc8eb63c6568 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -99,8 +99,23 @@ void process_srcu(struct work_struct *work);
}
/*
- * define and init a srcu struct at build time.
- * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it.
+ * Define and initialize a srcu struct at build time.
+ * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
+ *
+ * Note that although DEFINE_STATIC_SRCU() hides the name from other
+ * files, the per-CPU variable rules nevertheless require that the
+ * chosen name be globally unique. These rules also prohibit use of
+ * DEFINE_STATIC_SRCU() within a function. If these rules are too
+ * restrictive, declare the srcu_struct manually. For example, in
+ * each file:
+ *
+ * static struct srcu_struct my_srcu;
+ *
+ * Then, before the first use of each my_srcu, manually initialize it:
+ *
+ * init_srcu_struct(&my_srcu);
+ *
+ * See include/linux/percpu-defs.h for the rules on per-CPU variables.
*/
#define __DEFINE_SRCU(name, is_static) \
static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\