On Thu, May 09, 2019 at 02:09:03PM +0200, Daniel Vetter wrote:
> Fix this by creating a prinkt_safe_up() which calls wake_up_process
> outside of the spinlock. This isn't correct in full generality, but
> good enough for console_lock:
>
> - console_lock doesn't use interruptible or killable or timeout down()
> calls, hence an up() is the only thing that can wake up a process.
Wrong :/ Any task can be woken at any random time. We must, at all
times, assume spurious wakeups will happen.
> +void printk_safe_up(struct semaphore *sem)
> +{
> + unsigned long flags;
> + struct semaphore_waiter *waiter = NULL;
> +
> + raw_spin_lock_irqsave(&sem->lock, flags);
> + if (likely(list_empty(&sem->wait_list))) {
> + sem->count++;
> + } else {
> + waiter = list_first_entry(&sem->wait_list,
> + struct semaphore_waiter, list);
> + list_del(&waiter->list);
> + waiter->up = true;
> + }
> + raw_spin_unlock_irqrestore(&sem->lock, flags);
> +
> + if (waiter) /* protected by being sole wake source */
> + wake_up_process(waiter->task);
> +}
> +EXPORT_SYMBOL(printk_safe_up);
Since its only used from printk, that EXPORT really isn't needed.
Something like the below might work.
---
kernel/locking/semaphore.c | 26 +++++++++++++-------------
1 file changed, 13 insertions(+), 13 deletions(-)
diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index 561acdd39960..ac0a67e95aac 100644
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -38,7 +38,6 @@ static noinline void __down(struct semaphore *sem);
static noinline int __down_interruptible(struct semaphore *sem);
static noinline int __down_killable(struct semaphore *sem);
static noinline int __down_timeout(struct semaphore *sem, long timeout);
-static noinline void __up(struct semaphore *sem);
/**
* down - acquire the semaphore
@@ -178,14 +177,24 @@ EXPORT_SYMBOL(down_timeout);
*/
void up(struct semaphore *sem)
{
+ struct semaphore_waiter *waiter;
+ DEFINE_WAKE_Q(wake_q);
unsigned long flags;
raw_spin_lock_irqsave(&sem->lock, flags);
- if (likely(list_empty(&sem->wait_list)))
+ if (likely(list_empty(&sem->wait_list))) {
sem->count++;
- else
- __up(sem);
+ goto unlock;
+ }
+
+ waiter = list_first_entry(&sem->wait_list, struct semaphore_waiter,
list);
+ list_del(&waiter->list);
+ waiter->up = true;
+ wake_q_add(&wake_q, waiter->task);
+unlock:
raw_spin_unlock_irqrestore(&sem->lock, flags);
+
+ wake_up_q(&wake_q);
}
EXPORT_SYMBOL(up);
@@ -252,12 +261,3 @@ static noinline int __sched __down_timeout(struct
semaphore *sem, long timeout)
{
return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout);
}
-
-static noinline void __sched __up(struct semaphore *sem)
-{
- struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
- struct semaphore_waiter, list);
- list_del(&waiter->list);
- waiter->up = true;
- wake_up_process(waiter->task);
-}
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