linux-kernel - [PATCH tip/core/rcu 09/19] rcu: Protect uses of ->jiffies_stall with ACCESS

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Date:	Mon, 28 Apr 2014 16:56:22 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	oleg@...hat.com, sbw@....edu,
	Himangi Saraogi <himangi774@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 09/19] rcu: Protect uses of ->jiffies_stall with ACCESS_ONCE()

From: Himangi Saraogi <himangi774@...il.com>

Some of the accesses to the rcu_state structure's ->jiffies_stall
field are unprotected. This patch protects them with ACCESS_ONCE().
The following coccinelle script was used to acheive this:
/* coccinelle script to protect uses of ->jiffies_stall with ACCESS_ONCE() */
@@
identifier a;
@@
(
	ACCESS_ONCE(a->jiffies_stall)
|
-	a->jiffies_stall
+	ACCESS_ONCE(a->jiffies_stall)
)

Signed-off-by: Himangi Saraogi <himangi774@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tiny_plugin.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
index 431528520562..858c56569127 100644
--- a/kernel/rcu/tiny_plugin.h
+++ b/kernel/rcu/tiny_plugin.h
@@ -144,7 +144,7 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
 		return;
 	rcp->ticks_this_gp++;
 	j = jiffies;
-	js = rcp->jiffies_stall;
+	js = ACCESS_ONCE(rcp->jiffies_stall);
 	if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
 		pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
 		       rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
@@ -152,17 +152,17 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
 		dump_stack();
 	}
 	if (*rcp->curtail && ULONG_CMP_GE(j, js))
-		rcp->jiffies_stall = jiffies +
+		ACCESS_ONCE(rcp->jiffies_stall) = jiffies +
 			3 * rcu_jiffies_till_stall_check() + 3;
 	else if (ULONG_CMP_GE(j, js))
-		rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
+		ACCESS_ONCE(rcp->jiffies_stall) = jiffies + rcu_jiffies_till_stall_check();
 }
 
 static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
 {
 	rcp->ticks_this_gp = 0;
 	rcp->gp_start = jiffies;
-	rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
+	ACCESS_ONCE(rcp->jiffies_stall) = jiffies + rcu_jiffies_till_stall_check();
 }
 
 static void check_cpu_stalls(void)
-- 
1.8.1.5

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