linux-kernel - [RFC PATCH] drm/i915: Don't panic on non-empty list of free cachelines

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Message-Id: <20190405121331.6524-1-janusz.krzysztofik@linux.intel.com>
Date:   Fri,  5 Apr 2019 14:13:31 +0200
From:   Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>
To:     Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        michal.wajdeczko@...el.com, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Janusz Krzysztofik <janusz.krzysztofik@...el.com>
Subject: [RFC PATCH] drm/i915: Don't panic on non-empty list of free cachelines

From: Janusz Krzysztofik <janusz.krzysztofik@...el.com>

If there are active users of a device during driver unbind, the driver
now panics on non-empty list of free cachelines.

By design, chachelines which are not in use are kept on a list of free
chachelines associated with a timeline and rmoved from that list either
when in use or when the timeline is destroyed.  Timelines in turn are
assigned to open file descriptors.

As long as a device file is open, its associated timeline with its list
of free cachelines will be hopefully destroyed on device close, either
while outstanding execlists are destroyed or on i915_timeline_put()
called directly, so as long as device file descriptors are protected
from unwanted user activities by the device being marked unplugged,
there should be no reason to panic.

Moreover, timeline mutex which is destroyed right after the check for
emptyness of a free cacheline list succeeds is never used to protect
that list, only a list of active cachelines, so it can be freely
destroyed even if the former is not empty.

Simply remove the GEM_BUG_ON(!list_empty(&gt->hwsp_free_list)); line
from i915_timelines_fini().

Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@...el.com>
---
 drivers/gpu/drm/i915/i915_timeline.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_timeline.c b/drivers/gpu/drm/i915/i915_timeline.c
index b2202d2e58a2..1f23c2dcc0da 100644
--- a/drivers/gpu/drm/i915/i915_timeline.c
+++ b/drivers/gpu/drm/i915/i915_timeline.c
@@ -325,7 +325,6 @@ void i915_timelines_fini(struct drm_i915_private *i915)
 	struct i915_gt_timelines *gt = &i915->gt.timelines;

 	GEM_BUG_ON(!list_empty(&gt->active_list));
-	GEM_BUG_ON(!list_empty(&gt->hwsp_free_list));

 	mutex_destroy(&gt->mutex);
 }
-- 
2.20.1