From 51816e9e113934281b44f1a352852ef7631e75ea Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Fri, 24 May 2019 15:42:22 -0400 Subject: locking/lock_events: Use this_cpu_add() when necessary The kernel test robot has reported that the use of __this_cpu_add() causes bug messages like: BUG: using __this_cpu_add() in preemptible [00000000] code: ... Given the imprecise nature of the count and the possibility of resetting the count and doing the measurement again, this is not really a big problem to use the unprotected __this_cpu_*() functions. To make the preemption checking code happy, the this_cpu_*() functions will be used if CONFIG_DEBUG_PREEMPT is defined. The imprecise nature of the locking counts are also documented with the suggestion that we should run the measurement a few times with the counts reset in between to get a better picture of what is going on under the hood. Fixes: a8654596f0371 ("locking/rwsem: Enable lock event counting") Suggested-by: Linus Torvalds Signed-off-by: Waiman Long Signed-off-by: Linus Torvalds --- kernel/locking/lock_events.h | 42 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 40 insertions(+), 2 deletions(-) (limited to 'kernel/locking') diff --git a/kernel/locking/lock_events.h b/kernel/locking/lock_events.h index feb1acc54611..46b71af8eef2 100644 --- a/kernel/locking/lock_events.h +++ b/kernel/locking/lock_events.h @@ -30,13 +30,51 @@ enum lock_events { */ DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]); +/* + * The purpose of the lock event counting subsystem is to provide a low + * overhead way to record the number of specific locking events by using + * percpu counters. It is the percpu sum that matters, not specifically + * how many of them happens in each cpu. + * + * It is possible that the same percpu counter may be modified in both + * the process and interrupt contexts. For architectures that perform + * percpu operation with multiple instructions, it is possible to lose + * count if a process context percpu update is interrupted in the middle + * and the same counter is updated in the interrupt context. Therefore, + * the generated percpu sum may not be precise. The error, if any, should + * be small and insignificant. + * + * For those architectures that do multi-instruction percpu operation, + * preemption in the middle and moving the task to another cpu may cause + * a larger error in the count. Again, this will be few and far between. + * Given the imprecise nature of the count and the possibility of resetting + * the count and doing the measurement again, this is not really a big + * problem. + * + * To get a better picture of what is happening under the hood, it is + * suggested that a few measurements should be taken with the counts + * reset in between to stamp out outliner because of these possible + * error conditions. + * + * To minimize overhead, we use __this_cpu_*() in all cases except when + * CONFIG_DEBUG_PREEMPT is defined. In this particular case, this_cpu_*() + * will be used to avoid the appearance of unwanted BUG messages. + */ +#ifdef CONFIG_DEBUG_PREEMPT +#define lockevent_percpu_inc(x) this_cpu_inc(x) +#define lockevent_percpu_add(x, v) this_cpu_add(x, v) +#else +#define lockevent_percpu_inc(x) __this_cpu_inc(x) +#define lockevent_percpu_add(x, v) __this_cpu_add(x, v) +#endif + /* * Increment the PV qspinlock statistical counters */ static inline void __lockevent_inc(enum lock_events event, bool cond) { if (cond) - __this_cpu_inc(lockevents[event]); + lockevent_percpu_inc(lockevents[event]); } #define lockevent_inc(ev) __lockevent_inc(LOCKEVENT_ ##ev, true) @@ -44,7 +82,7 @@ static inline void __lockevent_inc(enum lock_events event, bool cond) static inline void __lockevent_add(enum lock_events event, int inc) { - __this_cpu_add(lockevents[event], inc); + lockevent_percpu_add(lockevents[event], inc); } #define lockevent_add(ev, c) __lockevent_add(LOCKEVENT_ ##ev, c) -- cgit v1.2.3 From c942fddf8793b2013be8c901b47d0a8dc02bf99f Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 27 May 2019 08:55:06 +0200 Subject: treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 Based on 3 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public license as published by the free software foundation either version 2 of the license or at your option any later version this program is distributed in the hope that it will be useful but without any warranty without even the implied warranty of merchantability or fitness for a particular purpose see the gnu general public license for more details this program is free software you can redistribute it and or modify it under the terms of the gnu general public license as published by the free software foundation either version 2 of the license or at your option any later version [author] [kishon] [vijay] [abraham] [i] [kishon]@[ti] [com] this program is distributed in the hope that it will be useful but without any warranty without even the implied warranty of merchantability or fitness for a particular purpose see the gnu general public license for more details this program is free software you can redistribute it and or modify it under the terms of the gnu general public license as published by the free software foundation either version 2 of the license or at your option any later version [author] [graeme] [gregory] [gg]@[slimlogic] [co] [uk] [author] [kishon] [vijay] [abraham] [i] [kishon]@[ti] [com] [based] [on] [twl6030]_[usb] [c] [author] [hema] [hk] [hemahk]@[ti] [com] this program is distributed in the hope that it will be useful but without any warranty without even the implied warranty of merchantability or fitness for a particular purpose see the gnu general public license for more details extracted by the scancode license scanner the SPDX license identifier GPL-2.0-or-later has been chosen to replace the boilerplate/reference in 1105 file(s). Signed-off-by: Thomas Gleixner Reviewed-by: Allison Randal Reviewed-by: Richard Fontana Reviewed-by: Kate Stewart Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190527070033.202006027@linutronix.de Signed-off-by: Greg Kroah-Hartman --- kernel/locking/qrwlock.c | 11 +---------- kernel/locking/qspinlock.c | 11 +---------- kernel/locking/qspinlock_stat.h | 10 +--------- 3 files changed, 3 insertions(+), 29 deletions(-) (limited to 'kernel/locking') diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c index c7471c3fb798..fe9ca92faa2a 100644 --- a/kernel/locking/qrwlock.c +++ b/kernel/locking/qrwlock.c @@ -1,16 +1,7 @@ +// SPDX-License-Identifier: GPL-2.0-or-later /* * Queued read/write locks * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. * * Authors: Waiman Long diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index e14b32c69639..2473f10c6956 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -1,16 +1,7 @@ +// SPDX-License-Identifier: GPL-2.0-or-later /* * Queued spinlock * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P. * (C) Copyright 2013-2014,2018 Red Hat, Inc. * (C) Copyright 2015 Intel Corp. diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h index 54152670ff24..e625bb410aa2 100644 --- a/kernel/locking/qspinlock_stat.h +++ b/kernel/locking/qspinlock_stat.h @@ -1,13 +1,5 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ /* - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. * * Authors: Waiman Long */ -- cgit v1.2.3