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

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Message-ID: <20151206015436.GM28602@linux.vnet.ibm.com>
Date:	Sat, 5 Dec 2015 17:54:36 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Josh Triplett <josh@...htriplett.org>
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 05:04:21PM -0800, Josh Triplett wrote:
> 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 *"

Good point, fixed!

> > +{
> > +	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.

I added the const.

However, I left the array in the .h file.  The issue is that the #defines
really have to be in the tree.h file.  Given that, if I move the array
elsewhere, they will very likely drift out of sync.  So this sounds like
a job for the compiler/linker...

Ah, but there is another approach.  It turns out that tree.h in included
only from tree.c and tree_trace.c.  And tree_trace.c defines a CPP symbol
RCU_TREE_NONCORE that is used elsewhere in tree.h to keep tree_trace.c's
mitts off a number of attractive but dangerous functions.  So I just put
the array under "#ifndef RCU_TREE_NONCORE".

Fair enough?

							Thanx, Paul

> > +	"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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