Re: [PATCH tip/core/rcu 27/45] rcutorture: Export RCU grace-period kthread wait state to rcutorture

[josh@joshtriplett.org]

On Mon, Apr 28, 2014 at 05:25:15PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> This commit allows rcutorture to print additional state for the
> RCU grace-period kthreads in cases where RCU seems reluctant to
> start a new grace period.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Should something reset gp_state after fqs finishes?

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

>  include/linux/rcutiny.h |  4 ++++
>  include/linux/rcutree.h |  1 +
>  kernel/rcu/rcutorture.c |  1 +
>  kernel/rcu/tree.c       | 17 +++++++++++++++++
>  kernel/rcu/tree.h       |  8 +++++++-
>  5 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 425c659d54e5..d40a6a451330 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -119,6 +119,10 @@ static inline void rcu_sched_force_quiescent_state(void)
>  {
>  }
>  
> +static inline void show_rcu_gp_kthreads(void)
> +{
> +}
> +
>  static inline void rcu_cpu_stall_reset(void)
>  {
>  }
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index a59ca05fd4e3..3e2f5d432743 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -84,6 +84,7 @@ extern unsigned long rcutorture_vernum;
>  long rcu_batches_completed(void);
>  long rcu_batches_completed_bh(void);
>  long rcu_batches_completed_sched(void);
> +void show_rcu_gp_kthreads(void);
>  
>  void rcu_force_quiescent_state(void);
>  void rcu_bh_force_quiescent_state(void);
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 50c26a7b6d97..15af04177e7e 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -1033,6 +1033,7 @@ rcu_torture_printk(char *page)
>  				"??? Writer stall state %d g%lu c%lu f%#x\n",
>  				rcu_torture_writer_state,
>  				gpnum, completed, flags);
> +		show_rcu_gp_kthreads();
>  		rcutorture_trace_dump();
>  	}
>  	rtcv_snap = rcu_torture_current_version;
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 032106df7391..3107bd935b2b 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -280,6 +280,21 @@ void rcu_bh_force_quiescent_state(void)
>  EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
>  
>  /*
> + * Show the state of the grace-period kthreads.
> + */
> +void show_rcu_gp_kthreads(void)
> +{
> +	struct rcu_state *rsp;
> +
> +	for_each_rcu_flavor(rsp) {
> +		pr_info("%s: wait state: %d ->state: %#lx\n",
> +			rsp->name, rsp->gp_state, rsp->gp_kthread->state);
> +		/* sched_show_task(rsp->gp_kthread); */
> +	}
> +}
> +EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
> +
> +/*
>   * Record the number of times rcutorture tests have been initiated and
>   * terminated.  This information allows the debugfs tracing stats to be
>   * correlated to the rcutorture messages, even when the rcutorture module
> @@ -1611,6 +1626,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
>  			trace_rcu_grace_period(rsp->name,
>  					       ACCESS_ONCE(rsp->gpnum),
>  					       TPS("reqwait"));
> +			rsp->gp_state = RCU_GP_WAIT_GPS;
>  			wait_event_interruptible(rsp->gp_wq,
>  						 ACCESS_ONCE(rsp->gp_flags) &
>  						 RCU_GP_FLAG_INIT);
> @@ -1638,6 +1654,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
>  			trace_rcu_grace_period(rsp->name,
>  					       ACCESS_ONCE(rsp->gpnum),
>  					       TPS("fqswait"));
> +			rsp->gp_state = RCU_GP_WAIT_FQS;
>  			ret = wait_event_interruptible_timeout(rsp->gp_wq,
>  					((gf = ACCESS_ONCE(rsp->gp_flags)) &
>  					 RCU_GP_FLAG_FQS) ||
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index 75dc3c39a02a..c2fd1e722879 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -406,7 +406,8 @@ struct rcu_state {
>  	unsigned long completed;		/* # of last completed gp. */
>  	struct task_struct *gp_kthread;		/* Task for grace periods. */
>  	wait_queue_head_t gp_wq;		/* Where GP task waits. */
> -	int gp_flags;				/* Commands for GP task. */
> +	short gp_flags;				/* Commands for GP task. */
> +	short gp_state;				/* GP kthread sleep state. */
>  
>  	/* End of fields guarded by root rcu_node's lock. */
>  
> @@ -469,6 +470,11 @@ struct rcu_state {
>  #define RCU_GP_FLAG_INIT 0x1	/* Need grace-period initialization. */
>  #define RCU_GP_FLAG_FQS  0x2	/* Need grace-period quiescent-state forcing. */
>  
> +/* Values for rcu_state structure's gp_flags field. */
> +#define RCU_GP_WAIT_INIT 0	/* Initial state. */
> +#define RCU_GP_WAIT_GPS  1	/* Wait for grace-period start. */
> +#define RCU_GP_WAIT_FQS  2	/* Wait for force-quiescent-state time. */
> +
>  extern struct list_head rcu_struct_flavors;
>  
>  /* Sequence through rcu_state structures for each RCU flavor. */
> -- 
> 1.8.1.5
>