From 7bda799fa26399160183b2df0c96a76f4a1e0a58 Mon Sep 17 00:00:00 2001 From: Yunfeng Ye Date: Wed, 29 Dec 2021 12:12:55 +0800 Subject: [PATCH] tick/sched: Reduce seqcount held scope in tick_do_update_jiffies64() mainline inclusion from mainline-5.11-rc1 commit 94ad2e3cedb82af034f6d97c58022f162b669f9b category: feature feature: Deep isolation bugzilla: https://gitee.com/openeuler/kernel/issues/I4N00D CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=94ad2e3cedb82af034f6d97c58022f162b669f9b -------------------------------- If jiffies are up to date already (caller lost the race against another CPU) there is no point to change the sequence count. Doing that just forces other CPUs into the seqcount retry loop in tick_nohz_next_event() for nothing. Just bail out early. [ tglx: Rewrote most of it ] Signed-off-by: Yunfeng Ye Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20201117132006.462195901@linutronix.de Reviewed-by: Chao Liu Reviewed-by: Chen Hui Acked-by: Xie XiuQi Signed-off-by: Zheng Zengkai --- kernel/time/tick-sched.c | 47 +++++++++++++++++++--------------------- 1 file changed, 22 insertions(+), 25 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 82a56b8bcd60..a2a26a8feae6 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -84,38 +84,35 @@ static void tick_do_update_jiffies64(ktime_t now) /* Reevaluate with jiffies_lock held */ raw_spin_lock(&jiffies_lock); + if (ktime_before(now, tick_next_period)) { + raw_spin_unlock(&jiffies_lock); + return; + } + write_seqcount_begin(&jiffies_seq); - delta = ktime_sub(now, last_jiffies_update); - if (delta >= tick_period) { + last_jiffies_update = ktime_add(last_jiffies_update, tick_period); - delta = ktime_sub(delta, tick_period); - last_jiffies_update = ktime_add(last_jiffies_update, - tick_period); + delta = ktime_sub(now, tick_next_period); + if (unlikely(delta >= tick_period)) { + /* Slow path for long idle sleep times */ + s64 incr = ktime_to_ns(tick_period); - /* Slow path for long timeouts */ - if (unlikely(delta >= tick_period)) { - s64 incr = ktime_to_ns(tick_period); + ticks = ktime_divns(delta, incr); - ticks = ktime_divns(delta, incr); + last_jiffies_update = ktime_add_ns(last_jiffies_update, + incr * ticks); + } - last_jiffies_update = ktime_add_ns(last_jiffies_update, - incr * ticks); - } - do_timer(++ticks); + do_timer(++ticks); + + /* + * Keep the tick_next_period variable up to date. WRITE_ONCE() + * pairs with the READ_ONCE() in the lockless quick check above. + */ + WRITE_ONCE(tick_next_period, + ktime_add(last_jiffies_update, tick_period)); - /* - * Keep the tick_next_period variable up to date. - * WRITE_ONCE() pairs with the READ_ONCE() in the lockless - * quick check above. - */ - WRITE_ONCE(tick_next_period, - ktime_add(last_jiffies_update, tick_period)); - } else { - write_seqcount_end(&jiffies_seq); - raw_spin_unlock(&jiffies_lock); - return; - } write_seqcount_end(&jiffies_seq); raw_spin_unlock(&jiffies_lock); update_wall_time(); -- GitLab