From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Sat, 7 Jul 2012 12:57:03 +0000 (-0700)
Subject: rcu: Add random PROVE_RCU_DELAY to grace-period initialization
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=661a85dc0d2ec0404e3b80909e413a9d5e42a239;p=GitHub%2FLineageOS%2Fandroid_kernel_samsung_universal7580.git

rcu: Add random PROVE_RCU_DELAY to grace-period initialization

Preemption greatly raised the probability of certain types of race
conditions, so this commit adds an anti-heisenbug to greatly increase
the collision cross section, also known as the probability of occurrence.

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

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 145f27fe3a1..f0f3a18c0a2 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -52,6 +52,7 @@
 #include <linux/prefetch.h>
 #include <linux/delay.h>
 #include <linux/stop_machine.h>
+#include <linux/random.h>
 
 #include "rcutree.h"
 #include <trace/events/rcu.h>
@@ -1087,6 +1088,10 @@ static int rcu_gp_init(struct rcu_state *rsp)
 					    rnp->level, rnp->grplo,
 					    rnp->grphi, rnp->qsmask);
 		raw_spin_unlock_irq(&rnp->lock);
+#ifdef CONFIG_PROVE_RCU_DELAY
+		if ((random32() % (rcu_num_nodes * 8)) == 0)
+			schedule_timeout_uninterruptible(2);
+#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
 		cond_resched();
 	}