We met a ksoftirqd 100% issue, the perf top shows kernel is busy
with tasklet_action(), but no actual action is shown. From dumped
kernel, there's only one disabled tasklet on the tasklet_vec.
tasklet_action might be handled after tasklet is disabled, this will
make disabled tasklet stayed on tasklet_vec. tasklet_action will not
handle disabled tasklet, but place it on the tail of tasklet_vec,
still raise softirq for this tasklet. Things will become worse if
device driver uses tasklet_disable on its device remove/close code.
The disabled tasklet will stay on the vec, frequently __raise_softirq_off()
and make ksoftirqd wakeup even if no tasklets need to be handled.
This patch introduced a new TASKLET_STATE_HI bit to indicate HI_SOFTIRQ,
in tasklet_action(), simply ignore the disabled tasklet and don't raise
the softirq nr. In my previous patch, I remove tasklet_hi_enable() since
it is the same as tasklet_enable(). So only tasklet_enable() needs to be
modified, if tasklet state is changed from disable to enable, use
__tasklet_schedule() to put it on the right vec.
Signed-off-by: Xiaotian Feng <dannyf...@tencent.com>
Cc: Andrew Morton <a...@linux-foundation.org>
---
include/linux/interrupt.h | 12 ++++++++++--
kernel/softirq.c | 10 +++++-----
2 files changed, 15 insertions(+), 7 deletions(-)
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 5e4e617..7e5bb00 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -521,7 +521,8 @@ struct tasklet_struct name = { NULL, 0, ATOMIC_INIT(1),
func, data }
enum
{
TASKLET_STATE_SCHED, /* Tasklet is scheduled for execution */
- TASKLET_STATE_RUN /* Tasklet is running (SMP only) */
+ TASKLET_STATE_RUN, /* Tasklet is running (SMP only) */
+ TASKLET_STATE_HI /* Tasklet is HI_SOFTIRQ */
};
#ifdef CONFIG_SMP
@@ -593,7 +594,14 @@ static inline void tasklet_disable(struct tasklet_struct
*t)
static inline void tasklet_enable(struct tasklet_struct *t)
{
smp_mb__before_atomic_dec();
- atomic_dec(&t->count);
+ if (atomic_dec_and_test(&t->count)) {
+ if (!test_bit(TASKLET_STATE_SCHED, &t->state))
+ return;
+ if (test_bit(TASKLET_STATE_HI, &t->state))
+ __tasklet_hi_schedule(t);
+ else
+ __tasklet_schedule(t);
+ }
}
static inline void tasklet_hi_enable(struct tasklet_struct *t)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index cc96bdc..6d77aef 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -431,6 +431,7 @@ void __tasklet_hi_schedule(struct tasklet_struct *t)
*__this_cpu_read(tasklet_hi_vec.tail) = t;
__this_cpu_write(tasklet_hi_vec.tail, &(t->next));
raise_softirq_irqoff(HI_SOFTIRQ);
+ set_bit(TASKLET_STATE_HI, &t->state);
local_irq_restore(flags);
}
@@ -442,6 +443,7 @@ void __tasklet_hi_schedule_first(struct tasklet_struct *t)
t->next = __this_cpu_read(tasklet_hi_vec.head);
__this_cpu_write(tasklet_hi_vec.head, t);
+ set_bit(TASKLET_STATE_HI, &t->state);
__raise_softirq_irqoff(HI_SOFTIRQ);
}
@@ -467,10 +469,9 @@ static void tasklet_action(struct softirq_action *a)
if (!test_and_clear_bit(TASKLET_STATE_SCHED,
&t->state))
BUG();
t->func(t->data);
- tasklet_unlock(t);
- continue;
- }
+ }
tasklet_unlock(t);
+ continue;
}
local_irq_disable();
@@ -502,10 +503,9 @@ static void tasklet_hi_action(struct softirq_action *a)
if (!test_and_clear_bit(TASKLET_STATE_SCHED,
&t->state))
BUG();
t->func(t->data);
- tasklet_unlock(t);
- continue;
}
tasklet_unlock(t);
+ continue;
}
local_irq_disable();
--
1.7.9.5
--
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