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>

diff --git a/kernel/exit.c b/kernel/exit.c
index 4b4042f..752d2c0 100644 (file)
--- 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 470d08c..500aaf6 100644 (file)
--- 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 b795231..5c233e0 100644 (file)
--- 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 3feab4a..a94466d 100644 (file)
--- 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)