genirq: Get rid of unnecessary IRQTF_DIED flag

Currently IRQTF_DIED flag is set when a IRQ thread handler calls do_exit()
But also PF_EXITING per process flag gets set when a thread exits. This
fix eliminates the duplicate by using PF_EXITING flag.

Also, there is a race condition in exit_irq_thread(). In case a thread's
bit is cleared in desc->threads_oneshot (and the IRQ line gets unmasked),
but before IRQTF_DIED flag is set, a new interrupt might come in and set
just cleared bit again, this time forever. This fix throws IRQTF_DIED flag
away, eliminating the race as a result.

[ tglx: Test THREAD_EXITING first as suggested by Oleg ]

Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Link: http://lkml.kernel.org/r/20120309135958.GD2114@dhcp-26-207.brq.redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 4b4042f9bc6a..752d2c0abd19 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -935,8 +935,6 @@ void do_exit(long code)
                 schedule();
         }
 
-        exit_irq_thread();
-
         exit_signals(tsk);  /* sets PF_EXITING */
         /*
          * tsk->flags are checked in the futex code to protect against
@@ -945,6 +943,8 @@ void do_exit(long code)
         smp_mb();
         raw_spin_unlock_wait(&tsk->pi_lock);
 
+        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),