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_work_add(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>
Cc: David Howells <dhowells@redhat.com>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Gordeev <agordeev@redhat.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Smith <dsmith@redhat.com>
Cc: "Frank Ch. Eigler" <fche@redhat.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 33 insertions, 37 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 3d93325e0b1a..3ecd096e5d4d 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 bb32326afe87..4d1f8f897414 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);
+
+        pr_err("genirq: 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;
@@ -815,44 +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);
-
-        pr_err("genirq: 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)