Commit cd82f37a authored Aug 04, 2017 by Chris Wilson Committed by Jani Nikula Aug 07, 2017

drm/i915/shrinker: Wrap need_resched() inside preempt-disable



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@linux.intel.com>
Reported-by: Tomi Sarvela <tomi.p.sarvela@intel.com>
Fixes: 290271de ("drm/i915: Spin for struct_mutex inside shrinker")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.13-rc1+
Link: https://patchwork.freedesktop.org/patch/msgid/20170804104135.26805-1-chris@chris-wilson.co.uk


Tested-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
(cherry picked from commit 6cb0c6ad)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

parent b5fa57dd

drivers/gpu/drm/i915/i915_gem_shrinker.c

+8 −3

Original line number	Original line	Diff line number	Diff line
	@@ -43,16 +43,21 @@ static bool shrinker_lock(struct drm_i915_private dev_priv, bool unlock)
	return true;		return true;

	case MUTEX_TRYLOCK_FAILED:		case MUTEX_TRYLOCK_FAILED:
			*unlock = false;
			preempt_disable();
	do {		do {
	cpu_relax();		cpu_relax();
	if (mutex_trylock(&dev_priv->drm.struct_mutex)) {		if (mutex_trylock(&dev_priv->drm.struct_mutex)) {
	case MUTEX_TRYLOCK_SUCCESS:
	*unlock = true;		*unlock = true;
	return true;		break;
	}		}
	} while (!need_resched());		} while (!need_resched());
			preempt_enable();
			return *unlock;

	return false;		case MUTEX_TRYLOCK_SUCCESS:
			*unlock = true;
			return true;
	}		}

	BUG();		BUG();