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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: Chris 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: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
This commit is contained in:
Chris Wilson 2017-09-11 09:41:26 +01:00
parent f46f156ea7
commit 81c0ed21aa
2 changed files with 22 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
drivers/gpu/drm/i915/Kconfig
View File

@ -12,6 +12,7 @@ config DRM_I915
select DRM_PANEL select DRM_PANEL
select DRM_MIPI_DSI select DRM_MIPI_DSI
select RELAY select RELAY
select IRQ_WORK
# i915 depends on ACPI_VIDEO when ACPI is enabled # i915 depends on ACPI_VIDEO when ACPI is enabled
# but for select to work, need to select ACPI_VIDEO's dependencies, ick # but for select to work, need to select ACPI_VIDEO's dependencies, ick
select BACKLIGHT_LCD_SUPPORT if ACPI select BACKLIGHT_LCD_SUPPORT if ACPI

27
drivers/gpu/drm/i915/i915_sw_fence.c
View File

@ -9,6 +9,7 @@
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/dma-fence.h> #include <linux/dma-fence.h>
#include <linux/irq_work.h>
#include <linux/reservation.h> #include <linux/reservation.h>
#include "i915_sw_fence.h" #include "i915_sw_fence.h"
@ -356,31 +357,44 @@ struct i915_sw_dma_fence_cb {
struct i915_sw_fence *fence; struct i915_sw_fence *fence;
struct dma_fence *dma; struct dma_fence *dma;
struct timer_list timer; struct timer_list timer;
struct irq_work work;
}; };
static void timer_i915_sw_fence_wake(unsigned long data) 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_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", pr_warn("asynchronous wait on fence %s:%s:%x timed out\n",
cb->dma->ops->get_driver_name(cb->dma), cb->dma->ops->get_driver_name(cb->dma),
cb->dma->ops->get_timeline_name(cb->dma), cb->dma->ops->get_timeline_name(cb->dma),
cb->dma->seqno); cb->dma->seqno);
dma_fence_put(cb->dma);
cb->dma = NULL;
i915_sw_fence_complete(cb->fence); i915_sw_fence_complete(fence);
cb->timer.function = NULL;
} }
static void dma_i915_sw_fence_wake(struct dma_fence *dma, static void dma_i915_sw_fence_wake(struct dma_fence *dma,
struct dma_fence_cb *data) struct dma_fence_cb *data)
{ {
struct i915_sw_dma_fence_cb *cb = container_of(data, typeof(*cb), base); 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); del_timer_sync(&cb->timer);
if (cb->timer.function)
i915_sw_fence_complete(cb->fence);
dma_fence_put(cb->dma); dma_fence_put(cb->dma);
kfree(cb); kfree(cb);
@ -414,6 +428,7 @@ int i915_sw_fence_await_dma_fence(struct i915_sw_fence *fence,
__setup_timer(&cb->timer, __setup_timer(&cb->timer,
timer_i915_sw_fence_wake, (unsigned long)cb, timer_i915_sw_fence_wake, (unsigned long)cb,
TIMER_IRQSAFE); TIMER_IRQSAFE);
init_irq_work(&cb->work, irq_i915_sw_fence_work);
if (timeout) { if (timeout) {
cb->dma = dma_fence_get(dma); cb->dma = dma_fence_get(dma);
mod_timer(&cb->timer, round_jiffies_up(jiffies + timeout)); mod_timer(&cb->timer, round_jiffies_up(jiffies + timeout));