When rt_runtime is modified from -1 to a valid control value, it may cause
the task to be throttled all the time. Then the task cannot be killed.
E.g:
The FIFO task A execution while(1):
#define _GNU_SOURCE
#include <sched.h>
#include <unistd.h>
int main(int argc,char *argv[])
{
struct sched_param param;
int priority = sched_get_priority_min(SCHED_FIFO);
param.sched_priority = priority;
sched_setscheduler(getpid(), SCHED_FIFO, ¶m);
while(1) {}
return 0;
}
Following the steps:
lihua@octopus ~ # echo -1 > /proc/sys/kernel/sched_rt_runtime_us
lihua@octopus ~ # /bin/rt_throttled &
lihua@octopus ~ # echo 950000 > /proc/sys/kernel/sched_rt_runtime_us
lihua@octopus ~ # ps aux | grep rt_throttled
root 7026 65.1 0.0 1848 180 ttyAMA0 R 01:27 0:26 /bin/rt_throttled
root 7068 0.0 0.0 4072 620 ttyAMA0 S+ 01:28 0:00 grep rt_throttled
lihua@octopus ~ # killall rt_throttled
lihua@octopus ~ # date
Thu Jan 1 01:28:30 UTC 1970
lihua@octopus ~ # date
Thu Jan 1 01:28:33 UTC 1970
lihua@octopus ~ # ps aux | grep rt_throttled
root 7026 41.0 0.0 1848 180 ttyAMA0 R 01:27 0:26 /bin/rt_throttled
root 7097 0.0 0.0 4072 576 ttyAMA0 S+ 01:28 0:00 grep rt_throttled
So the patch try to wake up the timer when rt runtime exceeded.
*** BLURB HERE ***
Li Hua (1):
sched/rt: Try to restart rt period timer when rt runtime exceeded
kernel/sched/rt.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
--
2.17.1
When rt_runtime is modified from -1 to a valid control value, it may
cause the task to be throttled all the time. Operations like the following
will trigger the bug. E.g:
1. echo -1 > /proc/sys/kernel/sched_rt_runtime_us
2. Run a FIFO task named A that executes while(1)
3. echo 950000 > /proc/sys/kernel/sched_rt_runtime_us
When rt_runtime is -1, The rt period timer will not be activated when task A
enqueued. And then the task will be throttled after setting rt_runtime to
950,000. The task will always be throttled because the rt period timer is not
activated.
Reported-by: Hulk Robot <[email protected]>
Signed-off-by: Li Hua <[email protected]>
---
kernel/sched/rt.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index bb945f8faeca..630f2cbe37d0 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -947,6 +947,23 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
return rt_task_of(rt_se)->prio;
}
+static inline void try_start_rt_bandwidth(struct rt_bandwidth *rt_b)
+{
+ raw_spin_lock(&rt_b->rt_runtime_lock);
+ if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF) {
+ raw_spin_unlock(&rt_b->rt_runtime_lock);
+ return;
+ }
+
+ if (!rt_b->rt_period_active) {
+ rt_b->rt_period_active = 1;
+ hrtimer_forward_now(&rt_b->rt_period_timer, rt_b->rt_period);
+ hrtimer_start_expires(&rt_b->rt_period_timer,
+ HRTIMER_MODE_ABS_PINNED_HARD);
+ }
+ raw_spin_unlock(&rt_b->rt_runtime_lock);
+}
+
static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
{
u64 runtime = sched_rt_runtime(rt_rq);
@@ -1027,11 +1044,16 @@ static void update_curr_rt(struct rq *rq)
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
+ int exceeded;
+
raw_spin_lock(&rt_rq->rt_runtime_lock);
rt_rq->rt_time += delta_exec;
- if (sched_rt_runtime_exceeded(rt_rq))
+ exceeded = sched_rt_runtime_exceeded(rt_rq);
+ if (exceeded)
resched_curr(rq);
raw_spin_unlock(&rt_rq->rt_runtime_lock);
+ if (exceeded)
+ try_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
}
}
}
@@ -2905,8 +2927,10 @@ static int sched_rt_global_validate(void)
static void sched_rt_do_global(void)
{
+ raw_spin_lock(&def_rt_bandwidth.rt_runtime_lock);
def_rt_bandwidth.rt_runtime = global_rt_runtime();
def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period());
+ raw_spin_unlock(&def_rt_bandwidth.rt_runtime_lock);
}
int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
--
2.17.1
On Mon, Nov 15, 2021 at 01:46:28AM +0000, Li Hua wrote:
> When rt_runtime is modified from -1 to a valid control value, it may
> cause the task to be throttled all the time. Operations like the following
> will trigger the bug. E.g:
> 1. echo -1 > /proc/sys/kernel/sched_rt_runtime_us
> 2. Run a FIFO task named A that executes while(1)
> 3. echo 950000 > /proc/sys/kernel/sched_rt_runtime_us
>
> When rt_runtime is -1, The rt period timer will not be activated when task A
> enqueued. And then the task will be throttled after setting rt_runtime to
> 950,000. The task will always be throttled because the rt period timer is not
> activated.
>
> Reported-by: Hulk Robot <[email protected]>
> Signed-off-by: Li Hua <[email protected]>
> ---
> kernel/sched/rt.c | 26 +++++++++++++++++++++++++-
> 1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index bb945f8faeca..630f2cbe37d0 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -947,6 +947,23 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
> return rt_task_of(rt_se)->prio;
> }
>
> +static inline void try_start_rt_bandwidth(struct rt_bandwidth *rt_b)
> +{
> + raw_spin_lock(&rt_b->rt_runtime_lock);
> + if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF) {
> + raw_spin_unlock(&rt_b->rt_runtime_lock);
> + return;
> + }
> +
> + if (!rt_b->rt_period_active) {
> + rt_b->rt_period_active = 1;
> + hrtimer_forward_now(&rt_b->rt_period_timer, rt_b->rt_period);
> + hrtimer_start_expires(&rt_b->rt_period_timer,
> + HRTIMER_MODE_ABS_PINNED_HARD);
> + }
> + raw_spin_unlock(&rt_b->rt_runtime_lock);
> +}
This is almost a verbatim copy of start_rt_bandwidth() surely we can do
better.
> +
> static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
> {
> u64 runtime = sched_rt_runtime(rt_rq);
> @@ -1027,11 +1044,16 @@ static void update_curr_rt(struct rq *rq)
> struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
>
> if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
> + int exceeded;
> +
> raw_spin_lock(&rt_rq->rt_runtime_lock);
> rt_rq->rt_time += delta_exec;
> - if (sched_rt_runtime_exceeded(rt_rq))
> + exceeded = sched_rt_runtime_exceeded(rt_rq);
> + if (exceeded)
> resched_curr(rq);
> raw_spin_unlock(&rt_rq->rt_runtime_lock);
> + if (exceeded)
> + try_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
> }
> }
> }
> @@ -2905,8 +2927,10 @@ static int sched_rt_global_validate(void)
>
> static void sched_rt_do_global(void)
> {
> + raw_spin_lock(&def_rt_bandwidth.rt_runtime_lock);
> def_rt_bandwidth.rt_runtime = global_rt_runtime();
> def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period());
> + raw_spin_unlock(&def_rt_bandwidth.rt_runtime_lock);
And that's just wrong I think; did you test this with lockdep enabled?
IIRC this lock is irq-safe, it has to be if you're using it form a timer
context.