linux-kernel - Re: [PATCH 2/3] rcu: Create rcu

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Message-ID: <20131003193206.GA17796@redhat.com>
Date:	Thu, 3 Oct 2013 21:32:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] rcu: Create rcu_sync infrastructure

On 10/03, Paul E. McKenney wrote:
>
> On Thu, Oct 03, 2013 at 08:47:19PM +0200, Oleg Nesterov wrote:
> >
> > Yes, but...
> >
> > I think it would be better to start with the patch below, this way
> > it would be easier a) to add the new ops (we need more anyway) and b)
> > use CONFIG_PROVE_RCU to avoid the unused members even if this is
> > really minor.
>
> I am fine with this as well, but I don't see the code that checks for
> the required RCU read-side critical section.

Because I believe this needs another patch ;) see below, didn't test
it yet.

(and yes, until I saw the patch from Peter I didn't realize we already
 have all necessary helpers as functions, somehow I tought that they
 are macros).

Oleg.

rcusync: add the CONFIG_PROVE_RCU checks

CHANGELOG
---

diff --git a/include/linux/rcusync.h b/include/linux/rcusync.h
index 30c6037..aa7e9e0 100644
--- a/include/linux/rcusync.h
+++ b/include/linux/rcusync.h
@@ -7,6 +7,9 @@
 struct rcu_sync_ops {
 	void (*sync)(void);
 	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+#ifdef CONFIG_PROVE_RCU
+	bool (*held)(void);
+#endif
 };
 
 struct rcu_sync_struct {
@@ -22,6 +25,9 @@ struct rcu_sync_struct {
 
 static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss)
 {
+#ifdef CONFIG_PROVE_RCU
+	WARN_ON(!rss->ops->held());
+#endif
 	return !rss->gp_state; /* GP_IDLE */
 }
 
diff --git a/kernel/rcusync.c b/kernel/rcusync.c
index 1cefb83..21f191f 100644
--- a/kernel/rcusync.c
+++ b/kernel/rcusync.c
@@ -6,18 +6,27 @@ enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
 
 #define	rss_lock	gp_wait.lock
 
+#ifdef CONFIG_PROVE_RCU
+#define __INIT_HELD(func)	.held = func,
+#else
+#define	__INIT_HELD(func)
+#endif
+
 struct rcu_sync_ops rcu_sync_ops_array[] = {
 	[RCU_SYNC] = {
 		.sync = synchronize_rcu,
 		.call = call_rcu,
+		__INIT_HELD(rcu_read_lock_held)
 	},
 	[RCU_SCHED_SYNC] = {
 		.sync = synchronize_sched,
 		.call = call_rcu_sched,
+		__INIT_HELD(rcu_read_lock_sched_held)
 	},
 	[RCU_BH_SYNC] = {
 		.sync = synchronize_rcu_bh,
 		.call = call_rcu_bh,
+		__INIT_HELD(rcu_read_lock_bh_held)
 	},
 };
 

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