genirq: Fix race condition when stopping the irq thread

BugLink: http://bugs.launchpad.net/bugs/902312

commit 550acb19269d65f32e9ac4ddb26c2b2070e37f1c upstream.

In irq_wait_for_interrupt(), the should_stop member is verified before
setting the task's state to TASK_INTERRUPTIBLE and calling schedule().
In case kthread_stop sets should_stop and wakes up the process after
should_stop is checked by the irq thread but before the task's state
is changed, the irq thread might never exit:

kthread_stop                    irq_wait_for_interrupt
------------                    ----------------------

                                 ...
...                              while (!kthread_should_stop()) {
kthread->should_stop = 1;
wake_up_process(k);
wait_for_completion(&kthread->exited);
...
                                     set_current_state(TASK_INTERRUPTIBLE);

                                     ...

                                     schedule();
                                 }

Fix this by checking if the thread should stop after modifying the
task's state.

[ tglx: Simplified it a bit ]

Signed-off-by: Ido Yariv <ido@wizery.com>
Link: http://lkml.kernel.org/r/1322740508-22640-1-git-send-email-ido@wizery.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 0a7840aeb0f..a1aadab09aa 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -620,8 +620,9 @@ static irqreturn_t irq_nested_primary_handler(int irq, void *dev_id)
 
 static int irq_wait_for_interrupt(struct irqaction *action)
 {
+        set_current_state(TASK_INTERRUPTIBLE);
+
         while (!kthread_should_stop()) {
-                set_current_state(TASK_INTERRUPTIBLE);
 
                 if (test_and_clear_bit(IRQTF_RUNTHREAD,
                                        &action->thread_flags)) {
@@ -629,7 +630,9 @@ static int irq_wait_for_interrupt(struct irqaction *action)
                         return 0;
                 }
                 schedule();
+                set_current_state(TASK_INTERRUPTIBLE);
         }
+        __set_current_state(TASK_RUNNING);
         return -1;
 }