From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <frederic@kernel.org>,
Yunfeng Ye <yeyunfeng@huawei.com>
Subject: [patch 1/7] tick/broadcast: Serialize access to tick_next_period
Date: Tue, 17 Nov 2020 14:19:43 +0100 [thread overview]
Message-ID: <20201117132006.061341507@linutronix.de> (raw)
In-Reply-To: 20201117131942.515430545@linutronix.de
tick_broadcast_setup_oneshot() accesses tick_next_period twice without any
serialization. This is wrong in two aspects:
- Reading it twice might make the broadcast data inconsistent if the
variable is updated concurrently.
- On 32bit systems the access might see an partial update
Protect it with jiffies_lock. That's safe as none of the callchains leading
up to this function can create a lock ordering violation:
timer interrupt
run_local_timers()
hrtimer_run_queues()
hrtimer_switch_to_hres()
tick_init_highres()
tick_switch_to_oneshot()
tick_broadcast_switch_to_oneshot()
or
tick_check_oneshot_change()
tick_nohz_switch_to_nohz()
tick_switch_to_oneshot()
tick_broadcast_switch_to_oneshot()
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/tick-broadcast.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -877,6 +877,22 @@ static void tick_broadcast_init_next_eve
}
}
+static inline ktime_t tick_get_next_period(void)
+{
+ ktime_t next;
+
+ /*
+ * Protect against concurrent updates (store /load tearing on
+ * 32bit). It does not matter if the time is already in the
+ * past. The broadcast device which is about to be programmed will
+ * fire in any case.
+ */
+ raw_spin_lock(&jiffies_lock);
+ next = tick_next_period;
+ raw_spin_unlock(&jiffies_lock);
+ return next;
+}
+
/**
* tick_broadcast_setup_oneshot - setup the broadcast device
*/
@@ -905,10 +921,11 @@ static void tick_broadcast_setup_oneshot
tick_broadcast_oneshot_mask, tmpmask);
if (was_periodic && !cpumask_empty(tmpmask)) {
+ ktime_t nextevt = tick_get_next_period();
+
clockevents_switch_state(bc, CLOCK_EVT_STATE_ONESHOT);
- tick_broadcast_init_next_event(tmpmask,
- tick_next_period);
- tick_broadcast_set_event(bc, cpu, tick_next_period);
+ tick_broadcast_init_next_event(tmpmask, nextevt);
+ tick_broadcast_set_event(bc, cpu, nextevt);
} else
bc->next_event = KTIME_MAX;
} else {
next prev parent reply other threads:[~2020-11-17 14:24 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-17 13:19 [patch 0/7] tick: Cleanups and reduce jiffies_seq held times Thomas Gleixner
2020-11-17 13:19 ` Thomas Gleixner [this message]
2020-11-19 9:55 ` [tip: timers/core] tick/broadcast: Serialize access to tick_next_period tip-bot2 for Thomas Gleixner
2020-11-17 13:19 ` [patch 2/7] tick: Document protections for tick related data Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-11-17 13:19 ` [patch 3/7] tick/sched: Use tick_next_period for lockless quick check Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-11-17 13:19 ` [patch 4/7] tick/sched: Reduce seqcount held scope in tick_do_update_jiffies64() Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Yunfeng Ye
2020-11-17 13:19 ` [patch 5/7] tick/sched: Optimize tick_do_update_jiffies64() further Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-11-17 13:19 ` [patch 6/7] tick/sched: Release seqcount before invoking calc_load_global() Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Yunfeng Ye
2020-11-17 13:19 ` [patch 7/7] tick: Get rid of tick_period Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
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