mutex_is_locked_by() checks the owner of the lock against current. This
is done by accessing a private member of struct mutex which works on
mainline but does not on RT.
I did not figure out, why this "lock-owner-check" and the "lock stealing
flag" is required. If the lock can not be acquire the lock (because it
would deadlock) then it can return -1.
The lock stealing makes actually no sense to me. If
shrinker_no_lock_stealing is true then the same functions
(i915_gem_purge(), i915_gem_shrink_all()) are called from
i915_gem_object_create_mmap_offset() as from i915_gem_inactive_shrink().
I haven't found a path in which i915_gem_inactive_shrink() is invoked
from i915_gem_object_create_mmap_offset() that means there is no way
shrinker_no_lock_stealing is true _and_ the lock is owned by the current
process.
Since I don't see why the i915 needs this hack while all other user do
not I recommend to remove this hack and return -1 in case of a dead
lock. Here is the patch.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
---
drivers/gpu/drm/i915/i915_drv.h | 1 -
drivers/gpu/drm/i915/i915_gem.c | 32 +++-----------------------------
2 files changed, 3 insertions(+), 30 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 01769e2..47f28ee 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -724,7 +724,6 @@ struct i915_gem_mm {
struct i915_hw_ppgtt *aliasing_ppgtt;
struct shrinker inactive_shrinker;
- bool shrinker_no_lock_stealing;
/**
* List of objects currently involved in rendering.
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 0e207e6..7949517 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1500,8 +1500,6 @@ static int i915_gem_object_create_mmap_offset(struct
drm_i915_gem_object *obj)
if (obj->base.map_list.map)
return 0;
- dev_priv->mm.shrinker_no_lock_stealing = true;
-
ret = drm_gem_create_mmap_offset(&obj->base);
if (ret != -ENOSPC)
goto out;
@@ -1521,8 +1519,6 @@ static int i915_gem_object_create_mmap_offset(struct
drm_i915_gem_object *obj)
i915_gem_shrink_all(dev_priv);
ret = drm_gem_create_mmap_offset(&obj->base);
out:
- dev_priv->mm.shrinker_no_lock_stealing = false;
-
return ret;
}
@@ -4368,19 +4364,6 @@ void i915_gem_release(struct drm_device *dev, struct
drm_file *file)
spin_unlock(&file_priv->mm.lock);
}
-static bool mutex_is_locked_by(struct mutex *mutex, struct task_struct *task)
-{
- if (!mutex_is_locked(mutex))
- return false;
-
-#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_MUTEXES)
- return mutex->owner == task;
-#else
- /* Since UP may be pre-empted, we cannot assume that we own the lock */
- return false;
-#endif
-}
-
static int
i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
{
@@ -4391,18 +4374,10 @@ i915_gem_inactive_shrink(struct shrinker *shrinker,
struct shrink_control *sc)
struct drm_device *dev = dev_priv->dev;
struct drm_i915_gem_object *obj;
int nr_to_scan = sc->nr_to_scan;
- bool unlock = true;
int cnt;
- if (!mutex_trylock(&dev->struct_mutex)) {
- if (!mutex_is_locked_by(&dev->struct_mutex, current))
- return 0;
-
- if (dev_priv->mm.shrinker_no_lock_stealing)
- return 0;
-
- unlock = false;
- }
+ if (!mutex_trylock(&dev->struct_mutex))
+ return -1;
if (nr_to_scan) {
nr_to_scan -= i915_gem_purge(dev_priv, nr_to_scan);
@@ -4421,7 +4396,6 @@ i915_gem_inactive_shrink(struct shrinker *shrinker,
struct shrink_control *sc)
if (obj->pin_count == 0 && obj->pages_pin_count == 0)
cnt += obj->base.size >> PAGE_SHIFT;
- if (unlock)
- mutex_unlock(&dev->struct_mutex);
+ mutex_unlock(&dev->struct_mutex);
return cnt;
}
--
1.7.6.5
