rcu: Document unique-name limitation for DEFINE_STATIC_SRCU() (9de630c4) · Commits · 戴 / test

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>

include/linux/srcu.h

+17 −2

Original line number	Diff line number	Diff line
		@@ -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);\

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