[PATCH] irq: Fix race condition when stopping the irq thread

[PATCH] irq: Fix race condition when stopping the irq thread

[Ido Yariv]

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.

Signed-off-by: Ido Yariv <ido@wizery.com>
Cc: stable@kernel.org
---
 kernel/irq/manage.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 0e2b179..3194d5e 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -631,7 +631,11 @@ static int irq_wait_for_interrupt(struct irqaction *action)
 			__set_current_state(TASK_RUNNING);
 			return 0;
 		}
-		schedule();
+
+		if (!kthread_should_stop())
+			schedule();
+		else
+			__set_current_state(TASK_RUNNING);
 	}
 	return -1;
 }
-- 
1.7.7.3

Re: [PATCH] irq: Fix race condition when stopping the irq thread

[Thomas Gleixner]

On Thu, 1 Dec 2011, Ido Yariv wrote:

> 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.

Good catch! I restructure it to:

--- tip.orig/kernel/irq/manage.c
+++ tip/kernel/irq/manage.c
@@ -623,8 +623,9 @@ static irqreturn_t irq_nested_primary_ha
 
 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)) {
@@ -632,7 +633,9 @@ static int irq_wait_for_interrupt(struct
 			return 0;
 		}
 		schedule();
+		set_current_state(TASK_INTERRUPTIBLE);
 	}
+	__set_current_state(TASK_RUNNING);
 	return -1;
 }
 
That saves us the extra conditional in the loop.

Thanks,

	tglx

[tip:irq/urgent] genirq: Fix race condition when stopping the irq thread

[tip-bot for Ido Yariv]

Commit-ID:  550acb19269d65f32e9ac4ddb26c2b2070e37f1c
Gitweb:     http://git.kernel.org/tip/550acb19269d65f32e9ac4ddb26c2b2070e37f1c
Author:     Ido Yariv <ido@wizery.com>
AuthorDate: Thu, 1 Dec 2011 13:55:08 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 2 Dec 2011 11:54:24 +0100

genirq: Fix race condition when stopping the irq thread

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>
Cc: stable@kernel.org
---
 kernel/irq/manage.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 0e2b179..1da999f 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -623,8 +623,9 @@ 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)) {
@@ -632,7 +633,9 @@ static int irq_wait_for_interrupt(struct irqaction *action)
 			return 0;
 		}
 		schedule();
+		set_current_state(TASK_INTERRUPTIBLE);
 	}
+	__set_current_state(TASK_RUNNING);
 	return -1;
 }