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Subject[PATCH v4 2/3] genirq: reimplement exit_irq_thread() hook via task_work_add()
exit_irq_thread() and task->irq_thread are needed to handle
the unexpected (and unlikely) exit of irq-thread.

We can use task_work instead and make this all private to
kernel/irq/manage.c, cleanup plus micro-optimization.

1. rename exit_irq_thread() to irq_thread_dtor(), make it
static, and move it up before irq_thread().

2. change irq_thread() to do task_queue_work(irq_thread_dtor)
at the start and task_work_cancel() before return.

tracehook_notify_resume() can never play with kthreads,
only do_exit()->exit_task_work() can call the callback
and this is what we want.

3. remove task_struct->irq_thread and the special hook
in do_exit().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/interrupt.h | 4 --
include/linux/sched.h | 10 +-----
kernel/exit.c | 2 -
kernel/irq/manage.c | 69 +++++++++++++++++++++-----------------------
4 files changed, 35 insertions(+), 50 deletions(-)
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 2aea5d2..1cdd4d0 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -142,8 +142,6 @@ request_any_context_irq(unsigned int irq, irq_handler_t handler,
extern int __must_check
request_percpu_irq(unsigned int irq, irq_handler_t handler,
const char *devname, void __percpu *percpu_dev_id);
-
-extern void exit_irq_thread(void);
#else

extern int __must_check
@@ -177,8 +175,6 @@ request_percpu_irq(unsigned int irq, irq_handler_t handler,
{
return request_irq(irq, handler, 0, devname, percpu_dev_id);
}
-
-static inline void exit_irq_thread(void) { }
#endif

extern void free_irq(unsigned int, void *);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index be004ac..e36edfb 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1346,11 +1346,6 @@ struct task_struct {
unsigned sched_reset_on_fork:1;
unsigned sched_contributes_to_load:1;

-#ifdef CONFIG_GENERIC_HARDIRQS
- /* IRQ handler threads */
- unsigned irq_thread:1;
-#endif
-
pid_t pid;
pid_t tgid;

@@ -1358,10 +1353,9 @@ struct task_struct {
/* Canary value for the -fstack-protector gcc feature */
unsigned long stack_canary;
#endif
-
- /*
+ /*
* pointers to (original) parent process, youngest child, younger sibling,
- * older sibling, respectively. (p->father can be replaced with
+ * older sibling, respectively. (p->father can be replaced with
* p->real_parent->pid)
*/
struct task_struct __rcu *real_parent; /* real parent process */
diff --git a/kernel/exit.c b/kernel/exit.c
index b82c38e..8135243 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -954,8 +954,6 @@ void do_exit(long code)

exit_task_work(tsk);

- exit_irq_thread();
-
if (unlikely(in_atomic()))
printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",
current->comm, task_pid_nr(current),
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 89a3ea8..525391c 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -14,6 +14,7 @@
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/sched.h>
+#include <linux/task_work.h>

#include "internals.h"

@@ -773,11 +774,39 @@ static void wake_threads_waitq(struct irq_desc *desc)
wake_up(&desc->wait_for_threads);
}

+static void irq_thread_dtor(struct task_work *unused)
+{
+ struct task_struct *tsk = current;
+ struct irq_desc *desc;
+ struct irqaction *action;
+
+ if (WARN_ON_ONCE(!(current->flags & PF_EXITING)))
+ return;
+
+ action = kthread_data(tsk);
+
+ printk(KERN_ERR
+ "exiting task \"%s\" (%d) is an active IRQ thread (irq %d)\n",
+ tsk->comm ? tsk->comm : "", tsk->pid, action->irq);
+
+ desc = irq_to_desc(action->irq);
+ /*
+ * If IRQTF_RUNTHREAD is set, we need to decrement
+ * desc->threads_active and wake possible waiters.
+ */
+ if (test_and_clear_bit(IRQTF_RUNTHREAD, &action->thread_flags))
+ wake_threads_waitq(desc);
+
+ /* Prevent a stale desc->threads_oneshot */
+ irq_finalize_oneshot(desc, action);
+}
+
/*
* Interrupt handler thread
*/
static int irq_thread(void *data)
{
+ struct task_work on_exit_work;
static const struct sched_param param = {
.sched_priority = MAX_USER_RT_PRIO/2,
};
@@ -793,7 +822,9 @@ static int irq_thread(void *data)
handler_fn = irq_thread_fn;

sched_setscheduler(current, SCHED_FIFO, &param);
- current->irq_thread = 1;
+
+ init_task_work(&on_exit_work, irq_thread_dtor, NULL);
+ task_work_add(current, &on_exit_work, false);

while (!irq_wait_for_interrupt(action)) {
irqreturn_t action_ret;
@@ -815,45 +846,11 @@ static int irq_thread(void *data)
* cannot touch the oneshot mask at this point anymore as
* __setup_irq() might have given out currents thread_mask
* again.
- *
- * Clear irq_thread. Otherwise exit_irq_thread() would make
- * fuzz about an active irq thread going into nirvana.
*/
- current->irq_thread = 0;
+ task_work_cancel(current, irq_thread_dtor);
return 0;
}

-/*
- * Called from do_exit()
- */
-void exit_irq_thread(void)
-{
- struct task_struct *tsk = current;
- struct irq_desc *desc;
- struct irqaction *action;
-
- if (!tsk->irq_thread)
- return;
-
- action = kthread_data(tsk);
-
- printk(KERN_ERR
- "exiting task \"%s\" (%d) is an active IRQ thread (irq %d)\n",
- tsk->comm ? tsk->comm : "", tsk->pid, action->irq);
-
- desc = irq_to_desc(action->irq);
-
- /*
- * If IRQTF_RUNTHREAD is set, we need to decrement
- * desc->threads_active and wake possible waiters.
- */
- if (test_and_clear_bit(IRQTF_RUNTHREAD, &action->thread_flags))
- wake_threads_waitq(desc);
-
- /* Prevent a stale desc->threads_oneshot */
- irq_finalize_oneshot(desc, action);
-}
-
static void irq_setup_forced_threading(struct irqaction *new)
{
if (!force_irqthreads)
--
1.5.5.1



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