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Message-ID: <20230128020051.2328465-1-liaoyu15@huawei.com> Date: Sat, 28 Jan 2023 10:00:51 +0800 From: Yu Liao <liaoyu15@...wei.com> To: <fweisbec@...il.com>, <tglx@...utronix.de>, <mingo@...nel.org> CC: <liaoyu15@...wei.com>, <liwei391@...wei.com>, <adobriyan@...il.com>, <mirsad.todorovac@....unizg.hr>, <linux-kernel@...r.kernel.org> Subject: [PATCH RFC] tick/nohz: fix data races in get_cpu_idle_time_us() selftest/proc/proc-uptime-001 complains: Euler:/mnt # while true; do ./proc-uptime-001; done proc-uptime-001: proc-uptime-001.c:41: main: Assertion `i1 >= i0' failed. proc-uptime-001: proc-uptime-001.c:41: main: Assertion `i1 >= i0' failed. /proc/uptime should be monotonically increasing. This occurs because the data races between get_cpu_idle_time_us and tick_nohz_stop_idle/tick_nohz_start_idle, for example: CPU0 CPU1 get_cpu_idle_time_us tick_nohz_idle_exit now = ktime_get(); tick_nohz_stop_idle update_ts_time_stats delta = ktime_sub(now, ts->idle_entrytime); ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta) ts->idle_entrytime = now now = ktime_get(); if (ts->idle_active && !nr_iowait_cpu(cpu)) { ktime_t delta = ktime_sub(now, ts->idle_entrytime); idle = ktime_add(ts->idle_sleeptime, delta); //idle is slightly greater than the actual value } else { idle = ts->idle_sleeptime; } ts->idle_active = 0 After this, idle = idle_sleeptime(actual idle value) + now(CPU0) - now(CPU1). If get_cpu_idle_time_us() is called immediately after ts->idle_active = 0, only ts->idle_sleeptime is returned, which is smaller than the previously read one, resulting in a non-monotonically increasing idle time. In addition, there are other data race scenarios not listed here. This patch introduce a lock to prevent data races. Fixes: a130e8fbc7de ("fs/proc/uptime.c: Fix idle time reporting in /proc/uptime") Signed-off-by: Yu Liao <liaoyu15@...wei.com> --- kernel/time/tick-sched.c | 15 ++++++++++++++- kernel/time/tick-sched.h | 1 + 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index b0e3c9205946..ad7d47098a58 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -36,7 +36,9 @@ /* * Per-CPU nohz control structure */ -static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); +static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched) = { + .idle_time_lock = __SPIN_LOCK_UNLOCKED(tick_cpu_sched.idle_time_lock), +}; struct tick_sched *tick_get_tick_sched(int cpu) { @@ -661,16 +663,24 @@ update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_upda static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) { + unsigned long flags; + + spin_lock_irqsave(&ts->idle_time_lock, flags); update_ts_time_stats(smp_processor_id(), ts, now, NULL); ts->idle_active = 0; + spin_unlock_irqrestore(&ts->idle_time_lock, flags); sched_clock_idle_wakeup_event(); } static void tick_nohz_start_idle(struct tick_sched *ts) { + unsigned long flags; + + spin_lock_irqsave(&ts->idle_time_lock, flags); ts->idle_entrytime = ktime_get(); ts->idle_active = 1; + spin_unlock_irqrestore(&ts->idle_time_lock, flags); sched_clock_idle_sleep_event(); } @@ -691,12 +701,14 @@ static void tick_nohz_start_idle(struct tick_sched *ts) u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); + unsigned long flags; ktime_t now, idle; if (!tick_nohz_active) return -1; now = ktime_get(); + spin_lock_irqsave(&ts->idle_time_lock, flags); if (last_update_time) { update_ts_time_stats(cpu, ts, now, last_update_time); idle = ts->idle_sleeptime; @@ -709,6 +721,7 @@ u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) idle = ts->idle_sleeptime; } } + spin_unlock_irqrestore(&ts->idle_time_lock, flags); return ktime_to_us(idle); diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h index 504649513399..a64d4781e7af 100644 --- a/kernel/time/tick-sched.h +++ b/kernel/time/tick-sched.h @@ -81,6 +81,7 @@ struct tick_sched { atomic_t tick_dep_mask; unsigned long last_tick_jiffies; unsigned int stalled_jiffies; + spinlock_t idle_time_lock; }; extern struct tick_sched *tick_get_tick_sched(int cpu); -- 2.25.1
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