On Thu, Jul 17, 2014 at 08:11:01PM -0400, Pranith Kumar wrote:
> On 07/17/2014 07:49 PM, Paul E. McKenney wrote:
> > On Thu, Jul 17, 2014 at 05:30:11PM -0400, Pranith Kumar wrote:
> >> Hi Paul,
> >>
> >> This is something similar to what you found yesterday with tick_nohz_full
> >> mask.
> >>
> >> --
> >> Pranith
> >>
> >> If we configure a kernel with CONFIG_NOCB_CPU=y,
> >> CONFIG_RCU_NOCB_CPU_NONE=y and
> >> CONFIG_CPUMASK_OFFSTACK=n and do not pass in a rcu_nocb= boot parameter,
> >> the
> >> cpumask rcu_nocb_mask can be garbage instead of NULL.
> >>
> >> Hence this commit replaces checks for rcu_nocb_mask == NULL with a check
> >> for
> >> have_rcu_nocb_mask.
> >>
> >> Signed-off-by: Pranith Kumar <bobby.pr...@gmail.com>
> >
> > Good catch! Could you please forward-port this to current rcu/dev?
> > This now includes the fix you mentioned above, which generates conflicts.
> >
> > Could you please also fix the use in rcu_is_nocb_cpu()?
> >
> > And please see the comment below.
> >
>
> Please find the fixed patch.
>
> --
> Pranith
>
>
> From: Pranith Kumar <bobby.pr...@gmail.com>
> Date: Thu, 17 Jul 2014 20:02:54 -0400
> Subject: [PATCH 1/1] rcu: Feedback comments
>
> If we configure a kernel with CONFIG_NOCB_CPU=y, CONFIG_RCU_NOCB_CPU_NONE=y
> and
> CONFIG_CPUMASK_OFFSTACK=n and do not pass in a rcu_nocb= boot parameter, the
> cpumask rcu_nocb_mask can be garbage instead of NULL.
>
> Hence this commit replaces checks for rcu_nocb_mask == NULL with a check for
> have_rcu_nocb_mask.
>
> Signed-off-by: Pranith Kumar <bobby.pr...@gmail.com>
> ---
> kernel/rcu/tree_plugin.h | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index ce8c331..8f987c1 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2053,9 +2053,10 @@ static void rcu_init_one_nocb(struct rcu_node *rnp)
> /* Is the specified CPU a no-CBs CPU? */
> bool rcu_is_nocb_cpu(int cpu)
> {
> - if (have_rcu_nocb_mask)
> - return cpumask_test_cpu(cpu, rcu_nocb_mask);
> - return false;
> + if (!have_rcu_nocb_mask)
> + return false;
> +
> + return cpumask_test_cpu(cpu, rcu_nocb_mask);
Hmmm... That was a subtle way to tell me that my feedback was bogus. ;-)
I guess I need to stop reviewing patches at 2AM local time.
Anyway, you are correct, this was OK to start with, so I am dropping
this hunk.
I queued the other two for 3.18.
Thanx, Paul
> }
> #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
>
> @@ -2540,7 +2541,7 @@ static void __init rcu_organize_nocb_kthreads(struct
> rcu_state *rsp)
> struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
> struct rcu_data *rdp_prev = NULL;
>
> - if (rcu_nocb_mask == NULL)
> + if (!have_rcu_nocb_mask)
> return;
> #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
> if (tick_nohz_full_running)
> @@ -2574,9 +2575,9 @@ static void __init rcu_organize_nocb_kthreads(struct
> rcu_state *rsp)
> /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
> static bool init_nocb_callback_list(struct rcu_data *rdp)
> {
> - if (rcu_nocb_mask == NULL ||
> - !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
> + if (!rcu_is_nocb_cpu(rdp->cpu))
> return false;
> +
> rdp->nxttail[RCU_NEXT_TAIL] = NULL;
> return true;
> }
> --
> 1.9.1
>
>
> --
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