From a7c8655b073d89303911c89d0fd9fc4be7631fbe Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 30 Nov 2017 15:36:35 -0800 Subject: [PATCH] sched/isolation: Eliminate NO_HZ_FULL_ALL Commit 6f1982fedd59 ("sched/isolation: Handle the nohz_full= parameter") broke CONFIG_NO_HZ_FULL_ALL=y kernels. This breakage is due to the code under CONFIG_NO_HZ_FULL_ALL failing to invoke the shiny new housekeeping functions. This means that rcutorture scenario TREE04 now emits RCU CPU stall warnings due to the RCU grace-period kthreads not being awakened at a time of their choosing, or perhaps even not at all: [ 27.731422] rcu_bh kthread starved for 21001 jiffies! g18446744073709551369 c18446744073709551368 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=3 [ 27.731423] rcu_bh I14936 9 2 0x80080000 [ 27.731435] Call Trace: [ 27.731440] __schedule+0x31a/0x6d0 [ 27.731442] schedule+0x31/0x80 [ 27.731446] schedule_timeout+0x15a/0x320 [ 27.731453] ? call_timer_fn+0x130/0x130 [ 27.731457] rcu_gp_kthread+0x66c/0xea0 [ 27.731458] ? rcu_gp_kthread+0x66c/0xea0 Because no one has complained about CONFIG_NO_HZ_FULL_ALL=y being broken, I hypothesize that no one is in fact using it, other than rcutorture. This commit therefore eliminates CONFIG_NO_HZ_FULL_ALL and updates rcutorture's config files to instead use the nohz_full= kernel parameter to put the desired CPUs into nohz_full mode. Fixes: 6f1982fedd59 ("sched/isolation: Handle the nohz_full= parameter") Reported-by: kernel test robot Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Cc: Thomas Gleixner Cc: Chris Metcalf Cc: Christoph Lameter Cc: Linus Torvalds Cc: Luiz Capitulino Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Rik van Riel Cc: Wanpeng Li Cc: Ingo Molnar Cc: John Stultz Cc: Jonathan Corbet --- Documentation/timers/NO_HZ.txt | 7 ------ kernel/time/Kconfig | 10 --------- kernel/time/tick-sched.c | 22 ++----------------- .../selftests/rcutorture/configs/rcu/TASKS03 | 1 - .../rcutorture/configs/rcu/TASKS03.boot | 2 +- .../selftests/rcutorture/configs/rcu/TREE04 | 1 - .../rcutorture/configs/rcu/TREE04.boot | 2 +- .../selftests/rcutorture/configs/rcu/TREE07 | 1 - 8 files changed, 4 insertions(+), 42 deletions(-) diff --git a/Documentation/timers/NO_HZ.txt b/Documentation/timers/NO_HZ.txt index 2dcaf9adb7a7..9591092da5e0 100644 --- a/Documentation/timers/NO_HZ.txt +++ b/Documentation/timers/NO_HZ.txt @@ -131,13 +131,6 @@ error message, and the boot CPU will be removed from the mask. Note that this means that your system must have at least two CPUs in order for CONFIG_NO_HZ_FULL=y to do anything for you. -Alternatively, the CONFIG_NO_HZ_FULL_ALL=y Kconfig parameter specifies -that all CPUs other than the boot CPU are adaptive-ticks CPUs. This -Kconfig parameter will be overridden by the "nohz_full=" boot parameter, -so that if both the CONFIG_NO_HZ_FULL_ALL=y Kconfig parameter and -the "nohz_full=1" boot parameter is specified, the boot parameter will -prevail so that only CPU 1 will be an adaptive-ticks CPU. - Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded. This is covered in the "RCU IMPLICATIONS" section below. diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index f6b5f19223d6..78eabc41eaa6 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -113,16 +113,6 @@ config NO_HZ_FULL endchoice -config NO_HZ_FULL_ALL - bool "Full dynticks system on all CPUs by default (except CPU 0)" - depends on NO_HZ_FULL - help - If the user doesn't pass the nohz_full boot option to - define the range of full dynticks CPUs, consider that all - CPUs in the system are full dynticks by default. - Note the boot CPU will still be kept outside the range to - handle the timekeeping duty. - config NO_HZ bool "Old Idle dynticks config" depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 29a5733eff83..ccd3782da0bf 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -405,30 +405,12 @@ static int tick_nohz_cpu_down(unsigned int cpu) return 0; } -static int tick_nohz_init_all(void) -{ - int err = -1; - -#ifdef CONFIG_NO_HZ_FULL_ALL - if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) { - WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n"); - return err; - } - err = 0; - cpumask_setall(tick_nohz_full_mask); - tick_nohz_full_running = true; -#endif - return err; -} - void __init tick_nohz_init(void) { int cpu, ret; - if (!tick_nohz_full_running) { - if (tick_nohz_init_all() < 0) - return; - } + if (!tick_nohz_full_running) + return; /* * Full dynticks uses irq work to drive the tick rescheduling on safe diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TASKS03 b/tools/testing/selftests/rcutorture/configs/rcu/TASKS03 index c70c51d5ded1..28568b72a31b 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TASKS03 +++ b/tools/testing/selftests/rcutorture/configs/rcu/TASKS03 @@ -9,5 +9,4 @@ CONFIG_PREEMPT=y CONFIG_HZ_PERIODIC=n CONFIG_NO_HZ_IDLE=n CONFIG_NO_HZ_FULL=y -CONFIG_NO_HZ_FULL_ALL=y #CHECK#CONFIG_RCU_EXPERT=n diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot b/tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot index cd2a188eeb6d..838297c58318 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot +++ b/tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot @@ -1 +1 @@ -rcutorture.torture_type=tasks +rcutorture.torture_type=tasks nohz_full=1 diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE04 b/tools/testing/selftests/rcutorture/configs/rcu/TREE04 index 27d22695d64c..24c9f6012e35 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE04 +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE04 @@ -7,7 +7,6 @@ CONFIG_PREEMPT=n CONFIG_HZ_PERIODIC=n CONFIG_NO_HZ_IDLE=n CONFIG_NO_HZ_FULL=y -CONFIG_NO_HZ_FULL_ALL=y CONFIG_RCU_FAST_NO_HZ=y CONFIG_RCU_TRACE=y CONFIG_HOTPLUG_CPU=n diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot index e34c33430447..e6071bb96c7d 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot @@ -1 +1 @@ -rcutorture.torture_type=rcu_bh rcutree.rcu_fanout_leaf=4 +rcutorture.torture_type=rcu_bh rcutree.rcu_fanout_leaf=4 nohz_full=1-7 diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE07 b/tools/testing/selftests/rcutorture/configs/rcu/TREE07 index 0f4759f4232e..d7afb271a586 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE07 +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE07 @@ -7,7 +7,6 @@ CONFIG_PREEMPT=n CONFIG_HZ_PERIODIC=n CONFIG_NO_HZ_IDLE=n CONFIG_NO_HZ_FULL=y -CONFIG_NO_HZ_FULL_ALL=n CONFIG_RCU_FAST_NO_HZ=n CONFIG_RCU_TRACE=y CONFIG_HOTPLUG_CPU=y -- 2.45.2