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Message-Id: <1524450747-22778-3-git-send-email-paulmck@linux.vnet.ibm.com> Date: Sun, 22 Apr 2018 19:32:08 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com, oleg@...hat.com, joel.opensrc@...il.com, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: [PATCH tip/core/rcu 03/22] rcu: Don't allocate rcu_nocb_mask if no one needs it Commit 44c65ff2e3b0 ("rcu: Eliminate NOCBs CPU-state Kconfig options") made allocation of rcu_nocb_mask depend only on the rcu_nocbs=, nohz_full=, or isolcpus= kernel boot parameters. However, it failed to change the initial value of rcu_init_nohz()'s local variable need_rcu_nocb_mask to false, which can result in useless allocation of an all-zero rcu_nocb_mask. This commit therefore fixes this bug by changing the initial value of need_rcu_nocb_mask to false. While we are in the area, also correct the error message that is printed when someone specifies that can-never-exist CPUs should be NOCBs CPUs. Reported-by: Byungchul Park <byungchul.park@....com> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> Acked-by: Byungchul Park <byungchul.park@....com> --- kernel/rcu/tree_plugin.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 6c5df18bbf2f..3566e4f6dfcc 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2283,7 +2283,7 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp) void __init rcu_init_nohz(void) { int cpu; - bool need_rcu_nocb_mask = true; + bool need_rcu_nocb_mask = false; struct rcu_state *rsp; #if defined(CONFIG_NO_HZ_FULL) @@ -2306,7 +2306,7 @@ void __init rcu_init_nohz(void) #endif /* #if defined(CONFIG_NO_HZ_FULL) */ if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { - pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); + pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); cpumask_and(rcu_nocb_mask, cpu_possible_mask, rcu_nocb_mask); } -- 2.5.2
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