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drm/i915/ttm: Fix illegal addition to shrinker list

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There's a small window of opportunity during which the adjust_lru()
function can be called with a GEM refcount of zero from the TTM
eviction code. This results in a kernel BUG().

Ensure that we don't attempt to modify the GEM shrinker lists unless
we have a GEM refcount.

Fixes: ebd4a8ec77 ("drm/i915/ttm: move shrinker management into adjust_lru")
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211110085527.1033475-1-thomas.hellstrom@linux.intel.com
This commit is contained in:
Thomas Hellström 2021-11-10 09:55:27 +01:00
parent 498f02b657
commit d3cb30f8dc
1 changed files with 21 additions and 10 deletions
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31
drivers/gpu/drm/i915/gem/i915_gem_ttm.c
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@ -771,18 +771,29 @@ void i915_ttm_adjust_lru(struct drm_i915_gem_object *obj)
*
* TODO: consider maybe also bumping the shrinker list here when we have
* already unpinned it, which should give us something more like an LRU.
*
* TODO: There is a small window of opportunity for this function to
* get called from eviction after we've dropped the last GEM refcount,
* but before the TTM deleted flag is set on the object. Avoid
* adjusting the shrinker list in such cases, since the object is
* not available to the shrinker anyway due to its zero refcount.
* To fix this properly we should move to a TTM shrinker LRU list for
* these objects.
*/
if (shrinkable != obj->mm.ttm_shrinkable) {
if (shrinkable) {
if (obj->mm.madv == I915_MADV_WILLNEED)
__i915_gem_object_make_shrinkable(obj);
else
__i915_gem_object_make_purgeable(obj);
} else {
i915_gem_object_make_unshrinkable(obj);
}
if (kref_get_unless_zero(&obj->base.refcount)) {
if (shrinkable != obj->mm.ttm_shrinkable) {
if (shrinkable) {
if (obj->mm.madv == I915_MADV_WILLNEED)
__i915_gem_object_make_shrinkable(obj);
else
__i915_gem_object_make_purgeable(obj);
} else {
i915_gem_object_make_unshrinkable(obj);
}
obj->mm.ttm_shrinkable = shrinkable;
obj->mm.ttm_shrinkable = shrinkable;
}
i915_gem_object_put(obj);
}
/*