From 6ccd2ecd422644277b7d8b37222e3af3f43ea9ae Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 11 Dec 2014 10:20:59 -0800 Subject: rcu: Improve diagnostics for spurious RCU CPU stall warnings The current RCU CPU stall warning code will print "Stall ended before state dump start" any time that the stall-warning code is triggered on a CPU that has already reported a quiescent state for the current grace period and if all quiescent states have been reported for the current grace period. However, a true stall can result in these symptoms, for example, by preventing RCU's grace-period kthreads from ever running This commit therefore checks for this condition, reporting the end of the stall only if one of the grace-period counters has actually advanced. Otherwise, it reports the last time that the grace-period kthread made meaningful progress. (In normal situations, the grace-period kthread should make meaningful progress at least every jiffies_till_next_fqs jiffies.) Reported-by: Miroslav Benes Signed-off-by: Paul E. McKenney Tested-by: Miroslav Benes --- kernel/rcu/tree.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'kernel/rcu/tree.h') diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index e300848..5ec81cf 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -488,6 +488,8 @@ struct rcu_state { /* due to no GP active. */ unsigned long gp_start; /* Time at which GP started, */ /* but in jiffies. */ + unsigned long gp_activity; /* Time of last GP kthread */ + /* activity in jiffies. */ unsigned long jiffies_stall; /* Time at which to check */ /* for CPU stalls. */ unsigned long jiffies_resched; /* Time at which to resched */ -- cgit v1.1