linux-kernel - [PATCH 9/9] softirq, timer: Use softirq_needs

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Date:   Fri, 5 May 2023 19:33:15 +0800
From:   Liu Jian <liujian56@...wei.com>
To:     <corbet@....net>, <paulmck@...nel.org>, <frederic@...nel.org>,
        <quic_neeraju@...cinc.com>, <joel@...lfernandes.org>,
        <josh@...htriplett.org>, <boqun.feng@...il.com>,
        <rostedt@...dmis.org>, <mathieu.desnoyers@...icios.com>,
        <jiangshanlai@...il.com>, <qiang1.zhang@...el.com>,
        <jstultz@...gle.com>, <tglx@...utronix.de>, <sboyd@...nel.org>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <peterz@...radead.org>, <frankwoo@...gle.com>,
        <Rhinewuwu@...gle.com>
CC:     <liujian56@...wei.com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <rcu@...r.kernel.org>,
        <netdev@...r.kernel.org>
Subject: [PATCH 9/9] softirq, timer: Use softirq_needs_break()

In the while loop of __run_timers(), because there are too many timers or
improper timer handler functions, if the processing time of the expired
timers is always greater than the time wheel's next_expiry, the function
will loop infinitely.

To prevent this, use the timeout/break logic provided by SoftIRQs. If the
running time exceeds the limit, break the loop and an additional
TIMER_SOFTIRQ is triggered.

Signed-off-by: Liu Jian <liujian56@...wei.com>
---
 kernel/time/timer.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 63a8ce7177dd..70744a469a39 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1992,7 +1992,7 @@ void timer_clear_idle(void)
  * __run_timers - run all expired timers (if any) on this CPU.
  * @base: the timer vector to be processed.
  */
-static inline void __run_timers(struct timer_base *base)
+static inline void __run_timers(struct timer_base *base, struct softirq_action *h)
 {
 	struct hlist_head heads[LVL_DEPTH];
 	int levels;
@@ -2020,6 +2020,12 @@ static inline void __run_timers(struct timer_base *base)
 
 		while (levels--)
 			expire_timers(base, heads + levels);
+
+		if (softirq_needs_break(h)) {
+			if (time_after_eq(jiffies, base->next_expiry))
+				__raise_softirq_irqoff(TIMER_SOFTIRQ);
+			break;
+		}
 	}
 	raw_spin_unlock_irq(&base->lock);
 	timer_base_unlock_expiry(base);
@@ -2032,9 +2038,9 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h)
 {
 	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
 
-	__run_timers(base);
+	__run_timers(base, h);
 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON))
-		__run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
+		__run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]), h);
 }
 
 /*
-- 
2.34.1