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>

4 files changed, 4 insertions, 15 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),
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 470d08c82bbe..500aaf67c546 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -60,7 +60,7 @@ static void irq_wake_thread(struct irq_desc *desc, struct irqaction *action)
          * device interrupt, so no irq storm is lurking. If the
          * RUNTHREAD bit is already set, nothing to do.
          */
-        if (test_bit(IRQTF_DIED, &action->thread_flags) ||
+        if ((action->thread->flags & PF_EXITING) ||
             test_and_set_bit(IRQTF_RUNTHREAD, &action->thread_flags))
                 return;
 
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index b7952316016a..5c233e0ea2c3 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -20,14 +20,12 @@ extern bool noirqdebug;
 /*
  * Bits used by threaded handlers:
  * IRQTF_RUNTHREAD - signals that the interrupt handler thread should run
- * IRQTF_DIED      - handler thread died
  * IRQTF_WARNED    - warning "IRQ_WAKE_THREAD w/o thread_fn" has been printed
  * IRQTF_AFFINITY  - irq thread is requested to adjust affinity
  * IRQTF_FORCED_THREAD  - irq action is force threaded
  */
 enum {
         IRQTF_RUNTHREAD,
-        IRQTF_DIED,
         IRQTF_WARNED,
         IRQTF_AFFINITY,
         IRQTF_FORCED_THREAD,
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 3feab4ab6877..a94466db73b2 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -845,17 +845,8 @@ void exit_irq_thread(void)
 
         desc = irq_to_desc(action->irq);
 
-        /*
-         * Prevent a stale desc->threads_oneshot. Must be called
-         * before setting the IRQTF_DIED flag.
-         */
+        /* Prevent a stale desc->threads_oneshot */
         irq_finalize_oneshot(desc, action, true);
-
-        /*
-         * Set the THREAD DIED flag to prevent further wakeups of the
-         * soon to be gone threaded handler.
-         */
-        set_bit(IRQTF_DIED, &action->flags);
 }
 
 static void irq_setup_forced_threading(struct irqaction *new)