rcu: Protect uses of ->jiffies_stall with ACCESS_ONCE()

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@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
index 4315285205626f7c27c38c774a4522a12b04adcf..858c5656912724c64e1ea20d5497edc9e8946b7d 100644 (file)
--- 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)