linux-kernel - Re: [PATCH tip/core/rcu 6/8] rcutorture: Print symbolic name for ->gp

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Message-ID: <20151205010421.GC27128@cloud>
Date:	Fri, 4 Dec 2015 17:04:21 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 6/8] rcutorture: Print symbolic name for
 ->gp_state

On Fri, Dec 04, 2015 at 04:23:50PM -0800, Paul E. McKenney wrote:
> Currently, ->gp_state is printed as an integer, which slows debugging.
> This commit therefore prints a symbolic name in addition to the integer.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> [ Updated to fix relational operator called out by Dan Carpenter. ]
> ---
>  kernel/rcu/tree.c | 15 +++++++++++++--
>  kernel/rcu/tree.h |  9 +++++++++
>  2 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 7b78c88e19a3..491c99a73996 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1187,6 +1187,16 @@ static void record_gp_stall_check_time(struct rcu_state *rsp)
>  }
>  
>  /*
> + * Convert a ->gp_state value to a character string.
> + */
> +static char *gp_state_getname(short gs)

Same comment about "const char *"

> +{
> +	if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
> +		return "???";
> +	return gp_state_names[gs];
> +}
> +
> +/*
>   * Complain about starvation of grace-period kthread.
>   */
>  static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
> @@ -1197,10 +1207,11 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
>  	j = jiffies;
>  	gpa = READ_ONCE(rsp->gp_activity);
>  	if (j - gpa > 2 * HZ) {
> -		pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x s%d ->state=%#lx\n",
> +		pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx\n",
>  		       rsp->name, j - gpa,
>  		       rsp->gpnum, rsp->completed,
> -		       rsp->gp_flags, rsp->gp_state,
> +		       rsp->gp_flags,
> +		       gp_state_getname(rsp->gp_state), rsp->gp_state,
>  		       rsp->gp_kthread ? rsp->gp_kthread->state : ~0);
>  		if (rsp->gp_kthread)
>  			sched_show_task(rsp->gp_kthread);
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index f32bebb6bc90..f0304988e3f8 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -544,6 +544,15 @@ struct rcu_state {
>  #define RCU_GP_DOING_FQS 4	/* Wait done for force-quiescent-state time. */
>  #define RCU_GP_CLEANUP   5	/* Grace-period cleanup started. */
>  #define RCU_GP_CLEANED   6	/* Grace-period cleanup complete. */
> +static char * const gp_state_names[] = {

Same comment about "const char * const", but also, should this really go
in a header file?  Do any circumstances exist where this header could
get included in more than one source file in a given build?  If so,
multiple copies of this array could potentially end up in the binary, if
the compiler fails to merge them.

> +	"RCU_GP_IDLE",
> +	"RCU_GP_WAIT_GPS",
> +	"RCU_GP_DONE_GPS",
> +	"RCU_GP_WAIT_FQS",
> +	"RCU_GP_DOING_FQS",
> +	"RCU_GP_CLEANUP",
> +	"RCU_GP_CLEANED",
> +};
>  
>  extern struct list_head rcu_struct_flavors;
>  
> -- 
> 2.5.2
> 
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