In order for us to successfully detect the end of a timeslice,
preemption must be disabled. Otherwise, inside the loop we may be
preempted many times without our noticing, and each time our timeslice
will be reset, invalidating need_resched()
Reported-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Reported-by: Tomi Sarvela <tomi.p.sarvela@xxxxxxxxx>
Fixes: 290271de34f6 ("drm/i915: Spin for struct_mutex inside shrinker")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: <drm-intel-fixes@xxxxxxxxxxxxxxxxxxxxx> # v4.13-rc1+
---
drivers/gpu/drm/i915/i915_gem_shrinker.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index 26697c9e317d..3a34dcf00174 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -43,16 +43,21 @@ static bool shrinker_lock(struct drm_i915_private *dev_priv, bool *unlock)
return true;
case MUTEX_TRYLOCK_FAILED:
+ *unlock = false;
+ preempt_disable();
do {
cpu_relax();
if (mutex_trylock(&dev_priv->drm.struct_mutex)) {
- case MUTEX_TRYLOCK_SUCCESS:
*unlock = true;
- return true;
+ break;
}
} while (!need_resched());
+ preempt_enable();
+ return *unlock;
- return false;
+ case MUTEX_TRYLOCK_SUCCESS:
+ *unlock = true;
+ return true;
}
BUG();
--
2.13.3
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