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Message-ID: <fb8d80434b2148e78c0032c6c70a8b4d@huawei.com>
Date: Fri, 10 Feb 2023 09:50:58 +0000
From: "liujian (CE)" <liujian56@...wei.com>
To: "jstultz@...gle.com" <jstultz@...gle.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"sboyd@...nel.org" <sboyd@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "liujian (CE)" <liujian56@...wei.com>
Subject: [Question] softlockup in run_timer_softirq
Hi,
During the syz test, we encountered many problems with various timer handler
functions softlockup.
We analyze __run_timers() and find the following problem.
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.
The following extreme test case can be used to reproduce the problem.
An extreme test case[1] is constructed to reproduce the problem.
Is this a problem or an unreasonable use?
Can we limit the running time of __run_timers() [2]?
Does anyone have a good idea to solve this problem?
Thank you.
[1]
#include <linux/module.h>
#include <linux/slab.h>
#include <asm-generic/delay.h>
static int stop = 1;
// timer num
static int size = 1000;
module_param(size, int, 0644);
MODULE_PARM_DESC(size, "size");
// Timeout of the timer
static int interval = 100;
module_param(interval, int, 0644);
MODULE_PARM_DESC(interval, "");
//elapsed time
static int dt = 200;
module_param(dt, int, 0644);
MODULE_PARM_DESC(dt, "");
struct wrapper {
struct timer_list timer;
spinlock_t lock;
};
struct wrapper *wr;
static void timer_func(struct timer_list *t)
{
struct wrapper *w = from_timer(w, t, timer);
spin_lock_bh(&(w->lock));
if (stop == 0) {
udelay(dt); // elapsed time
}
spin_unlock_bh(&(w->lock));
if (stop == 0) {
mod_timer(&(w->timer), jiffies + interval);
}
}
static int __init maint_init(void)
{
int i;
wr = (struct wrapper *)kzalloc(size*sizeof(struct wrapper), GFP_KERNEL);
for (i = 0; i < size; i++) {
struct wrapper *w = &wr[i];
spin_lock_init(&(w->lock));
timer_setup(&(w->timer), timer_func, 0);
mod_timer(&(w->timer), jiffies + 20);
}
stop = 0;
return 0;
}
static void __exit maint_exit(void)
{
int i;
stop = 1;
udelay(100);
for (i = 0; i < size; i++) {
struct wrapper *w = &wr[i];
del_timer_sync(&(w->timer));
}
kfree(wr);
}
module_init(maint_init);
module_exit(maint_exit);
MODULE_LICENSE("GPL");
insmod timer_test.ko size=1000 interval=100 dt=200
[2]
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 63a8ce7177dd..a215916f26cf 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -223,6 +223,9 @@ static DEFINE_MUTEX(timer_keys_mutex);
static void timer_update_keys(struct work_struct *work);
static DECLARE_WORK(timer_update_work, timer_update_keys);
+static unsigned int sysctl_timer_time_limit = 0;
+
+#ifdef CONFIG_SYSCTL
#ifdef CONFIG_SMP
static unsigned int sysctl_timer_migration = 1;
@@ -236,7 +239,6 @@ static void timers_update_migration(void)
static_branch_disable(&timers_migration_enabled);
}
-#ifdef CONFIG_SYSCTL
static int timer_migration_handler(struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
@@ -249,8 +251,12 @@ static int timer_migration_handler(struct ctl_table *table, int write,
mutex_unlock(&timer_keys_mutex);
return ret;
}
+#else
+static inline void timers_update_migration(void) { }
+#endif /* !CONFIG_SMP */
static struct ctl_table timer_sysctl[] = {
+#ifdef CONFIG_SMP
{
.procname = "timer_migration",
.data = &sysctl_timer_migration,
@@ -260,6 +266,15 @@ static struct ctl_table timer_sysctl[] = {
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
+#endif
+ {
+ .procname = "timer_time_limit",
+ .data = &sysctl_timer_time_limit,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ },
{}
};
@@ -270,9 +285,6 @@ static int __init timer_sysctl_init(void)
}
device_initcall(timer_sysctl_init);
#endif /* CONFIG_SYSCTL */
-#else /* CONFIG_SMP */
-static inline void timers_update_migration(void) { }
-#endif /* !CONFIG_SMP */
static void timer_update_keys(struct work_struct *work)
{
@@ -1992,7 +2004,7 @@ 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, unsigned long time_limit)
{
struct hlist_head heads[LVL_DEPTH];
int levels;
@@ -2020,6 +2032,13 @@ static inline void __run_timers(struct timer_base *base)
while (levels--)
expire_timers(base, heads + levels);
+
+ if (unlikely(time_limit &&
+ time_after_eq(jiffies, time_limit))) {
+ if (time_after_eq(jiffies, base->next_expiry))
+ raise_softirq(TIMER_SOFTIRQ);
+ break;
+ }
}
raw_spin_unlock_irq(&base->lock);
timer_base_unlock_expiry(base);
@@ -2031,10 +2050,14 @@ static inline void __run_timers(struct timer_base *base)
static __latent_entropy void run_timer_softirq(struct softirq_action *h)
{
struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
+ unsigned long time_limit = 0;
+
+ if (sysctl_timer_time_limit)
+ time_limit = jiffies + msecs_to_jiffies(sysctl_timer_time_limit);
- __run_timers(base);
+ __run_timers(base, time_limit);
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]), time_limit);
}
/*
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