The patch titled
Subject: tasklet: ignore disabled tasklet in tasklet_action()
has been added to the -mm tree. Its filename is
tasklet-ignore-disabled-tasklet-in-tasklet_action.patch
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------------------------------------------------------
From: Xiaotian Feng <xtfeng@xxxxxxxxx>
Subject: tasklet: ignore disabled tasklet in tasklet_action()
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 <dannyfeng@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/interrupt.h | 12 ++++++++++--
kernel/softirq.c | 8 ++++----
2 files changed, 14 insertions(+), 6 deletions(-)
diff -puN include/linux/interrupt.h~tasklet-ignore-disabled-tasklet-in-tasklet_action include/linux/interrupt.h
--- a/include/linux/interrupt.h~tasklet-ignore-disabled-tasklet-in-tasklet_action
+++ a/include/linux/interrupt.h
@@ -521,7 +521,8 @@ struct tasklet_struct name = { NULL, 0,
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(struc
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 -puN kernel/softirq.c~tasklet-ignore-disabled-tasklet-in-tasklet_action kernel/softirq.c
--- a/kernel/softirq.c~tasklet-ignore-disabled-tasklet-in-tasklet_action
+++ a/kernel/softirq.c
@@ -431,6 +431,7 @@ void __tasklet_hi_schedule(struct taskle
*__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
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 softir
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 sof
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();
_
Patches currently in -mm which might be from xtfeng@xxxxxxxxx are
linux-next.patch
tasklet-ignore-disabled-tasklet-in-tasklet_action.patch
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