linux-kernel - Re: [PATCH] percpu/module resevation: change resevation size iff X86

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Date:   Wed, 13 Mar 2019 14:22:55 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Barret Rhoden <brho@...gle.com>,
        Christopher Lameter <cl@...ux.com>,
        Dennis Zhou <dennis@...nel.org>,
        Eial Czerwacki <eial@...lemp.com>,
        linux-kernel@...r.kernel.org, Shai Fultheim <shai@...lemp.com>,
        Oren Twaig <oren@...lemp.com>
Subject: Re: [PATCH] percpu/module resevation: change resevation size iff
 X86_VSMP is set

On Wed, Mar 13, 2019 at 01:26:40PM -0700, Tejun Heo wrote:
> Hello,
> 
> On Wed, Mar 13, 2019 at 03:40:04PM -0400, Barret Rhoden wrote:
> > Are there any other alternatives?  Not using static SRCU in any code
> > that could be built as a module seems a little harsh.
> 
> Yes, allocate the srcu dynamically on module init and destroy on
> module exit.  That's how the other similar case got solved too.  We
> can't keep bumping up reserved size by the number of static SRCUs in
> modules.  It's mostly there to make trivial small things easier.  We
> don't lose anything meaningful by allocating srcu dynamically.

Should I define DEFINE_SRCU() and DEFINE_STATIC_SRCU() only if
!defined(MODULE)?

Untested (probably doesn't even build) patch below.

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 7f7c8c050f63..a979da9cf71f 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -105,6 +105,8 @@ struct srcu_struct {
  * Define and initialize a srcu struct at build time.
  * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
  *
+ * Build-time srcu_struct definition is not allowed in modules.
+ *
  * 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
@@ -120,11 +122,13 @@ struct srcu_struct {
  *
  * 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_data, name##_srcu_data);\
+#ifndef MODULE
+#  define __DEFINE_SRCU(name, is_static)				\
+	static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data);	\
 	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name##_srcu_data)
-#define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
-#define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
+#  define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
+#  define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
+#endif
 
 void synchronize_srcu_expedited(struct srcu_struct *ssp);
 void srcu_barrier(struct srcu_struct *ssp);
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 5ff797fd3715..7cf1e3aed695 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -496,9 +496,18 @@ static struct rcu_torture_ops rcu_busted_ops = {
  * Definitions for srcu torture testing.
  */
 
-DEFINE_STATIC_SRCU(srcu_ctl);
 static struct srcu_struct srcu_ctld;
-static struct srcu_struct *srcu_ctlp = &srcu_ctl;
+static struct srcu_struct *srcu_ctlp;
+
+#ifndef MODULE
+DEFINE_STATIC_SRCU(srcu_ctl);
+
+static void srcu_torture_init(void)
+{
+	rcu_sync_torture_init();
+	srcu_ctlp = &srcu_ctl;
+}
+#endif
 
 static int srcu_torture_read_lock(void) __acquires(srcu_ctlp)
 {
@@ -565,9 +574,10 @@ static void srcu_torture_synchronize_expedited(void)
 	synchronize_srcu_expedited(srcu_ctlp);
 }
 
+#ifndef MODULE
 static struct rcu_torture_ops srcu_ops = {
 	.ttype		= SRCU_FLAVOR,
-	.init		= rcu_sync_torture_init,
+	.init		= srcu_torture_init,
 	.readlock	= srcu_torture_read_lock,
 	.read_delay	= srcu_read_delay,
 	.readunlock	= srcu_torture_read_unlock,
@@ -581,25 +591,25 @@ static struct rcu_torture_ops srcu_ops = {
 	.irq_capable	= 1,
 	.name		= "srcu"
 };
+#endif
 
-static void srcu_torture_init(void)
+static void srcud_torture_init(void)
 {
 	rcu_sync_torture_init();
 	WARN_ON(init_srcu_struct(&srcu_ctld));
 	srcu_ctlp = &srcu_ctld;
 }
 
-static void srcu_torture_cleanup(void)
+static void srcud_torture_cleanup(void)
 {
 	cleanup_srcu_struct(&srcu_ctld);
-	srcu_ctlp = &srcu_ctl; /* In case of a later rcutorture run. */
 }
 
 /* As above, but dynamically allocated. */
 static struct rcu_torture_ops srcud_ops = {
 	.ttype		= SRCU_FLAVOR,
-	.init		= srcu_torture_init,
-	.cleanup	= srcu_torture_cleanup,
+	.init		= srcud_torture_init,
+	.cleanup	= srcud_torture_cleanup,
 	.readlock	= srcu_torture_read_lock,
 	.read_delay	= srcu_read_delay,
 	.readunlock	= srcu_torture_read_unlock,
@@ -617,8 +627,8 @@ static struct rcu_torture_ops srcud_ops = {
 /* As above, but broken due to inappropriate reader extension. */
 static struct rcu_torture_ops busted_srcud_ops = {
 	.ttype		= SRCU_FLAVOR,
-	.init		= srcu_torture_init,
-	.cleanup	= srcu_torture_cleanup,
+	.init		= srcud_torture_init,
+	.cleanup	= srcud_torture_cleanup,
 	.readlock	= srcu_torture_read_lock,
 	.read_delay	= rcu_read_delay,
 	.readunlock	= srcu_torture_read_unlock,