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, 2 insertions, 12 deletions

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index c91171599cb6..e68a8e53bb59 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 7930131abc1a..da013853a622 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1301,11 +1301,6 @@ 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;
 
@@ -1313,10 +1308,9 @@ 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 */