On Wed, Apr 22, 2009 at 11:48 AM, Shaohua Li <shaohua...@intel.com> wrote:
> drm_lock() does:
> for (;;) {
> __set_current_state(TASK_INTERRUPTIBLE);
> ...
> if (drm_lock_take(&master->lock, lock->context)) {
> <==== schedule() here
> master->lock.file_priv = file_priv;
> master->lock.lock_time = jiffies;
> atomic_inc(&dev->counts[_DRM_STAT_LOCKS]);
> break; /* Got lock */
> }
> ...
> }
> If a preempt occurs in marked line, the task already holds the lock but
> set to interruptible, then nobody can wakeup the task (except signal) and
> other tasks can't get the lock again. Am I missing anything?
Thomas you seem to have the best understanding of this code, can you
take a look and ack this?
Dave.
>
> Signed-off-by: Shaohua Li<shaohua...@intel.com>
> diff --git a/drivers/gpu/drm/drm_lock.c b/drivers/gpu/drm/drm_lock.c
> index e2f70a5..32fbca0 100644
> --- a/drivers/gpu/drm/drm_lock.c
> +++ b/drivers/gpu/drm/drm_lock.c
> @@ -76,6 +76,7 @@ int drm_lock(struct drm_device *dev, void *data, struct
> drm_file *file_priv)
> master->lock.user_waiters++;
> spin_unlock_bh(&master->lock.spinlock);
>
> + preempt_disable();
> for (;;) {
> __set_current_state(TASK_INTERRUPTIBLE);
> if (!master->lock.hw_lock) {
> @@ -90,18 +91,21 @@ int drm_lock(struct drm_device *dev, void *data, struct
> drm_file *file_priv)
> atomic_inc(&dev->counts[_DRM_STAT_LOCKS]);
> break; /* Got lock */
> }
> + preempt_enable_no_resched();
>
> /* Contention */
> schedule();
> + preempt_disable();
> if (signal_pending(current)) {
> ret = -EINTR;
> break;
> }
> }
> + __set_current_state(TASK_RUNNING);
> + preempt_enable();
> spin_lock_bh(&master->lock.spinlock);
> master->lock.user_waiters--;
> spin_unlock_bh(&master->lock.spinlock);
> - __set_current_state(TASK_RUNNING);
> remove_wait_queue(&master->lock.lock_queue, &entry);
>
> DRM_DEBUG("%d %s\n", lock->context,
>
>
>
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