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Commit 81c0ed21 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915/fence: Avoid del_timer_sync() from inside a timer 



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_wake() 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: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170911084135.22903-3-chris@chris-wilson.co.uk


Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
parent f46f156e

drivers/gpu/drm/i915/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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

drivers/gpu/drm/i915/i915_sw_fence.c

+21 −6
Original line number Diff line number Diff line
@@ -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));