A fence may be signaled from any context, including from inside a timer.
One example is timer_i915_sw_fence_wake() which is used to provide a
safety-net when waiting on an external fence. If the external fence is
not signaled within a timely fashion, we signal our fence on its behalf,
and so we then may process subsequent fences in the chain from within
that timer context.
Given that dma_i915_sw_fence_cb() may be from inside a timer, we cannot
then use del_timer_sync() as that requires the timer lock for itself. To
circumvent this, while trying to keep the signal propagation as low
latency as possible, move the completion into a worker and use a bit of
atomic switheroo to serialise the timer-callback and the dma-callback.
Testcase: igt/gem_eio/in-flight-external
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/Kconfig | 1 +
drivers/gpu/drm/i915/i915_sw_fence.c | 27 +++++++++++++++++++++------
2 files changed, 22 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
index e9e64e8e9765..dfd95889f4b7 100644
--- a/drivers/gpu/drm/i915/Kconfig
+++ b/drivers/gpu/drm/i915/Kconfig
@@ -12,6 +12,7 @@ config DRM_I915
select DRM_PANEL
select DRM_MIPI_DSI
select RELAY
+ select IRQ_WORK
# i915 depends on ACPI_VIDEO when ACPI is enabled
# but for select to work, need to select ACPI_VIDEO's dependencies, ick
select BACKLIGHT_LCD_SUPPORT if ACPI
diff --git a/drivers/gpu/drm/i915/i915_sw_fence.c b/drivers/gpu/drm/i915/i915_sw_fence.c
index f29540f922af..808ea4d5b962 100644
--- a/drivers/gpu/drm/i915/i915_sw_fence.c
+++ b/drivers/gpu/drm/i915/i915_sw_fence.c
@@ -9,6 +9,7 @@
#include <linux/slab.h>
#include <linux/dma-fence.h>
+#include <linux/irq_work.h>
#include <linux/reservation.h>
#include "i915_sw_fence.h"
@@ -356,31 +357,44 @@ struct i915_sw_dma_fence_cb {
struct i915_sw_fence *fence;
struct dma_fence *dma;
struct timer_list timer;
+ struct irq_work work;
};
static void timer_i915_sw_fence_wake(unsigned long data)
{
struct i915_sw_dma_fence_cb *cb = (struct i915_sw_dma_fence_cb *)data;
+ struct i915_sw_fence *fence;
+
+ fence = xchg(&cb->fence, NULL);
+ if (!fence)
+ return;
pr_warn("asynchronous wait on fence %s:%s:%x timed out\n",
cb->dma->ops->get_driver_name(cb->dma),
cb->dma->ops->get_timeline_name(cb->dma),
cb->dma->seqno);
- dma_fence_put(cb->dma);
- cb->dma = NULL;
- i915_sw_fence_complete(cb->fence);
- cb->timer.function = NULL;
+ i915_sw_fence_complete(fence);
}
static void dma_i915_sw_fence_wake(struct dma_fence *dma,
struct dma_fence_cb *data)
{
struct i915_sw_dma_fence_cb *cb = container_of(data, typeof(*cb), base);
+ struct i915_sw_fence *fence;
+
+ fence = xchg(&cb->fence, NULL);
+ if (fence)
+ i915_sw_fence_complete(fence);
+
+ irq_work_queue(&cb->work);
+}
+
+static void irq_i915_sw_fence_work(struct irq_work *wrk)
+{
+ struct i915_sw_dma_fence_cb *cb = container_of(wrk, typeof(*cb), work);
del_timer_sync(&cb->timer);
- if (cb->timer.function)
- i915_sw_fence_complete(cb->fence);
dma_fence_put(cb->dma);
kfree(cb);
@@ -414,6 +428,7 @@ int i915_sw_fence_await_dma_fence(struct i915_sw_fence *fence,
__setup_timer(&cb->timer,
timer_i915_sw_fence_wake, (unsigned long)cb,
TIMER_IRQSAFE);
+ init_irq_work(&cb->work, irq_i915_sw_fence_work);
if (timeout) {
cb->dma = dma_fence_get(dma);
mod_timer(&cb->timer, round_jiffies_up(jiffies + timeout));
--
2.14.1
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