Messages in this thread Patch in this message | | | Date | Fri, 3 Jun 2011 08:33:44 -0700 | From | "Paul E. McKenney" <> | Subject | Re: Mysterious CFQ crash and RCU |
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On Fri, Jun 03, 2011 at 09:45:14AM -0400, Vivek Goyal wrote: > On Thu, Jun 02, 2011 at 10:07:24PM -0700, Paul E. McKenney wrote: > > [..] > > > Thu May 26 10:47:20 CEST 2011 > > > /sys/kernel/debug/rcu/rcugp: > > > rcu_sched: completed=682249 gpnum=682250 > > > > 15 more seconds, a few thousand more grace periods. About 500 grace > > periods per second, which is quite reasonable on a single-CPU system. > > PaulB mentioned that crash happened at May 26 10:47:07. I am wondering > how are we able to sample the data after the crash. I am assuming > that above data gives information only before crash and does not > tell us anything about what happened just before crash. What am I missing. > > PaulM, in one of the mails you had mentioned that one could print > context switch id to make sure we did not block in rcu section. Would > you have quick pointer where is context switch id stored. May be > I can write a small patch for PaulB.
From what I can see, the task_struct nvcsw and nivcsw fields should do it, though I am not seeing where these are incremented.
So if these don't do what you need, the following (untested but trivial) patch will provide an rcu_switch_count in the task structure.
Thanx, Paul
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rcu: add diagnostic per-task context-switch count
Note that this is also incremented by softirqs.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/sched.h b/include/linux/sched.h index 2a8621c..5ef22e2 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1261,6 +1261,7 @@ struct task_struct { #ifdef CONFIG_RCU_BOOST struct rt_mutex *rcu_boost_mutex; #endif /* #ifdef CONFIG_RCU_BOOST */ + unsigned long rcu_switch_count; #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT) struct sched_info sched_info; diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 89419ff..080c6eb 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -154,6 +154,7 @@ void rcu_bh_qs(int cpu) */ void rcu_note_context_switch(int cpu) { + current->rcu_switch_count++; rcu_sched_qs(cpu); rcu_preempt_note_context_switch(cpu); }
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