Commit 0c1f8457 authored May 28, 2019 by Chris Wilson

drm/i915: Avoid refcount_inc on known zero count



In intel_wakeref_auto, we use refcount_inc_not_zero to detect the first
use and initialise the timer. On doing so, we have to avoid using
refcount_inc on that zero count as the debug code flags that as an
error:
	refcount_t: increment on 0; use-after-free.

Rearrange the code so that if we know the count is 0 and we are
initialising, we explicitly set it to 1.

Fixes: b27e35ae ("drm/i915: Keep user GGTT alive for a minimum of 250ms")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528154053.22004-1-chris@chris-wilson.co.uk

parent 81a04d2e

drivers/gpu/drm/i915/intel_wakeref.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -114,11 +114,11 @@ void intel_wakeref_auto(struct intel_wakeref_auto *wf, unsigned long timeout)

		if (!refcount_inc_not_zero(&wf->count)) {
		spin_lock_irqsave(&wf->lock, flags);
		if (!refcount_read(&wf->count)) {
		if (!refcount_inc_not_zero(&wf->count)) {
		GEM_BUG_ON(wf->wakeref);
		wf->wakeref = intel_runtime_pm_get_if_in_use(wf->i915);
		refcount_set(&wf->count, 1);
		}
		refcount_inc(&wf->count);
		spin_unlock_irqrestore(&wf->lock, flags);
		}

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