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Date: Fri, 18 Jul 2014 23:10:21 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Pranith Kumar <bobby.prani@...il.com> Cc: Josh Triplett <josh@...htriplett.org>, Steven Rostedt <rostedt@...dmis.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Lai Jiangshan <laijs@...fujitsu.com>, "open list:READ-COPY UPDATE..." <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 1/1] rcu: Check for have_rcu_nocb_mask instead of rcu_nocb_mask 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.prani@...il.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.prani@...il.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.prani@...il.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 > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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