drm: fix driver deadlock with AIGLX and reclaim_buffers_locked
Bugzilla Bug #9457
Add refcounting of user waiters to the DRM hardware lock, so that we can use
DRM_LOCK_CONT flag more conservatively.
Also add a kernel waiter refcount that if nonzero transfers the lock for the
kernel context when it is released. This is useful when waiting for idle and can be used for very simple fence object driver implementations for the new memory manager
Signed-off-by: Dave Airlie <airlied@linux.ie>
diff --git a/drivers/char/drm/drm_lock.c b/drivers/char/drm/drm_lock.c
index e9993ba..befd1af 100644
--- a/drivers/char/drm/drm_lock.c
+++ b/drivers/char/drm/drm_lock.c
@@ -35,9 +35,6 @@
#include "drmP.h"
-static int drm_lock_transfer(drm_device_t * dev,
- __volatile__ unsigned int *lock,
- unsigned int context);
static int drm_notifier(void *priv);
/**
@@ -80,6 +77,9 @@
return -EINVAL;
add_wait_queue(&dev->lock.lock_queue, &entry);
+ spin_lock(&dev->lock.spinlock);
+ dev->lock.user_waiters++;
+ spin_unlock(&dev->lock.spinlock);
for (;;) {
__set_current_state(TASK_INTERRUPTIBLE);
if (!dev->lock.hw_lock) {
@@ -87,7 +87,7 @@
ret = -EINTR;
break;
}
- if (drm_lock_take(&dev->lock.hw_lock->lock, lock.context)) {
+ if (drm_lock_take(&dev->lock, lock.context)) {
dev->lock.filp = filp;
dev->lock.lock_time = jiffies;
atomic_inc(&dev->counts[_DRM_STAT_LOCKS]);
@@ -101,12 +101,14 @@
break;
}
}
+ spin_lock(&dev->lock.spinlock);
+ dev->lock.user_waiters--;
+ spin_unlock(&dev->lock.spinlock);
__set_current_state(TASK_RUNNING);
remove_wait_queue(&dev->lock.lock_queue, &entry);
- DRM_DEBUG("%d %s\n", lock.context, ret ? "interrupted" : "has lock");
- if (ret)
- return ret;
+ DRM_DEBUG( "%d %s\n", lock.context, ret ? "interrupted" : "has lock" );
+ if (ret) return ret;
sigemptyset(&dev->sigmask);
sigaddset(&dev->sigmask, SIGSTOP);
@@ -127,14 +129,12 @@
}
}
- /* dev->driver->kernel_context_switch isn't used by any of the x86
- * drivers but is used by the Sparc driver.
- */
if (dev->driver->kernel_context_switch &&
dev->last_context != lock.context) {
dev->driver->kernel_context_switch(dev, dev->last_context,
lock.context);
}
+
return 0;
}
@@ -184,12 +184,8 @@
if (dev->driver->kernel_context_switch_unlock)
dev->driver->kernel_context_switch_unlock(dev);
else {
- drm_lock_transfer(dev, &dev->lock.hw_lock->lock,
- DRM_KERNEL_CONTEXT);
-
- if (drm_lock_free(dev, &dev->lock.hw_lock->lock,
- DRM_KERNEL_CONTEXT)) {
- DRM_ERROR("\n");
+ if (drm_lock_free(&dev->lock,lock.context)) {
+ /* FIXME: Should really bail out here. */
}
}
@@ -206,18 +202,26 @@
*
* Attempt to mark the lock as held by the given context, via the \p cmpxchg instruction.
*/
-int drm_lock_take(__volatile__ unsigned int *lock, unsigned int context)
+int drm_lock_take(drm_lock_data_t *lock_data,
+ unsigned int context)
{
unsigned int old, new, prev;
+ volatile unsigned int *lock = &lock_data->hw_lock->lock;
+ spin_lock(&lock_data->spinlock);
do {
old = *lock;
if (old & _DRM_LOCK_HELD)
new = old | _DRM_LOCK_CONT;
- else
- new = context | _DRM_LOCK_HELD;
+ else {
+ new = context | _DRM_LOCK_HELD |
+ ((lock_data->user_waiters + lock_data->kernel_waiters > 1) ?
+ _DRM_LOCK_CONT : 0);
+ }
prev = cmpxchg(lock, old, new);
} while (prev != old);
+ spin_unlock(&lock_data->spinlock);
+
if (_DRM_LOCKING_CONTEXT(old) == context) {
if (old & _DRM_LOCK_HELD) {
if (context != DRM_KERNEL_CONTEXT) {
@@ -227,7 +231,8 @@
return 0;
}
}
- if (new == (context | _DRM_LOCK_HELD)) {
+
+ if ((_DRM_LOCKING_CONTEXT(new)) == context && (new & _DRM_LOCK_HELD)) {
/* Have lock */
return 1;
}
@@ -246,13 +251,13 @@
* Resets the lock file pointer.
* Marks the lock as held by the given context, via the \p cmpxchg instruction.
*/
-static int drm_lock_transfer(drm_device_t * dev,
- __volatile__ unsigned int *lock,
+static int drm_lock_transfer(drm_lock_data_t *lock_data,
unsigned int context)
{
unsigned int old, new, prev;
+ volatile unsigned int *lock = &lock_data->hw_lock->lock;
- dev->lock.filp = NULL;
+ lock_data->filp = NULL;
do {
old = *lock;
new = context | _DRM_LOCK_HELD;
@@ -272,23 +277,32 @@
* Marks the lock as not held, via the \p cmpxchg instruction. Wakes any task
* waiting on the lock queue.
*/
-int drm_lock_free(drm_device_t * dev,
- __volatile__ unsigned int *lock, unsigned int context)
+int drm_lock_free(drm_lock_data_t *lock_data, unsigned int context)
{
unsigned int old, new, prev;
+ volatile unsigned int *lock = &lock_data->hw_lock->lock;
- dev->lock.filp = NULL;
+ spin_lock(&lock_data->spinlock);
+ if (lock_data->kernel_waiters != 0) {
+ drm_lock_transfer(lock_data, 0);
+ lock_data->idle_has_lock = 1;
+ spin_unlock(&lock_data->spinlock);
+ return 1;
+ }
+ spin_unlock(&lock_data->spinlock);
+
do {
old = *lock;
- new = 0;
+ new = _DRM_LOCKING_CONTEXT(old);
prev = cmpxchg(lock, old, new);
} while (prev != old);
+
if (_DRM_LOCK_IS_HELD(old) && _DRM_LOCKING_CONTEXT(old) != context) {
DRM_ERROR("%d freed heavyweight lock held by %d\n",
context, _DRM_LOCKING_CONTEXT(old));
return 1;
}
- wake_up_interruptible(&dev->lock.lock_queue);
+ wake_up_interruptible(&lock_data->lock_queue);
return 0;
}
@@ -322,3 +336,67 @@
} while (prev != old);
return 0;
}
+
+/**
+ * This function returns immediately and takes the hw lock
+ * with the kernel context if it is free, otherwise it gets the highest priority when and if
+ * it is eventually released.
+ *
+ * This guarantees that the kernel will _eventually_ have the lock _unless_ it is held
+ * by a blocked process. (In the latter case an explicit wait for the hardware lock would cause
+ * a deadlock, which is why the "idlelock" was invented).
+ *
+ * This should be sufficient to wait for GPU idle without
+ * having to worry about starvation.
+ */
+
+void drm_idlelock_take(drm_lock_data_t *lock_data)
+{
+ int ret = 0;
+
+ spin_lock(&lock_data->spinlock);
+ lock_data->kernel_waiters++;
+ if (!lock_data->idle_has_lock) {
+
+ spin_unlock(&lock_data->spinlock);
+ ret = drm_lock_take(lock_data, DRM_KERNEL_CONTEXT);
+ spin_lock(&lock_data->spinlock);
+
+ if (ret == 1)
+ lock_data->idle_has_lock = 1;
+ }
+ spin_unlock(&lock_data->spinlock);
+}
+EXPORT_SYMBOL(drm_idlelock_take);
+
+void drm_idlelock_release(drm_lock_data_t *lock_data)
+{
+ unsigned int old, prev;
+ volatile unsigned int *lock = &lock_data->hw_lock->lock;
+
+ spin_lock(&lock_data->spinlock);
+ if (--lock_data->kernel_waiters == 0) {
+ if (lock_data->idle_has_lock) {
+ do {
+ old = *lock;
+ prev = cmpxchg(lock, old, DRM_KERNEL_CONTEXT);
+ } while (prev != old);
+ wake_up_interruptible(&lock_data->lock_queue);
+ lock_data->idle_has_lock = 0;
+ }
+ }
+ spin_unlock(&lock_data->spinlock);
+}
+EXPORT_SYMBOL(drm_idlelock_release);
+
+
+int drm_i_have_hw_lock(struct file *filp)
+{
+ DRM_DEVICE;
+
+ return (priv->lock_count && dev->lock.hw_lock &&
+ _DRM_LOCK_IS_HELD(dev->lock.hw_lock->lock) &&
+ dev->lock.filp == filp);
+}
+
+EXPORT_SYMBOL(drm_i_have_hw_lock);