Re: [PATCH tip/core/rcu 2/8] rcutorture: Dump stack when GP kthread stalls

Paul E. McKenney
2015-12-06T01:44:49Z

On Fri, Dec 04, 2015 at 04:59:48PM -0800, Josh Triplett wrote:
> On Fri, Dec 04, 2015 at 04:23:46PM -0800, Paul E. McKenney wrote:
> > This commit increases debug information in the case where the grace-period
> > kthread is being prevented from running by dumping that kthread's stack.
>
> That's not everything this patch does; see below.
>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > ---
> > kernel/rcu/tree.c | 7 +++++--
> > 1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 81aa1cdc6bc9..7b78c88e19a3 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1196,12 +1196,15 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
> >
> > j = jiffies;
> > gpa = READ_ONCE(rsp->gp_activity);
> > - if (j - gpa > 2 * HZ)
> > + if (j - gpa > 2 * HZ) {
> > 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_kthread ? rsp->gp_kthread->state : 0);
> > + rsp->gp_kthread ? rsp->gp_kthread->state : ~0);
>
> The commit message doesn't explain this change. Could you please 1)
> document this change in the commit message, and 2) split it into a
> separate patch unless it directly relates to the other change (which
> doesn't seem like the case)?

Good point, especially given that it took me some time to remember why
that change was necessary. It is now in a separate commit, with a commit
log stating that this disambiguates the case where there is no RCU GP
kthread from the case where there is a TASK_RUNNING RCU GP kthread.

Thanx, Paul

> > + if (rsp->gp_kthread)
> > + sched_show_task(rsp->gp_kthread);
> > + }
> > }
> >
> > /*
> > --
> > 2.5.2
> >
>