drm/mm: Use clear_bit_unlock() for releasing the drm_mm_node()
A few callers need to serialise the destruction of their drm_mm_node and ensure it is removed from the drm_mm before freeing. However, to be completely sure that any access from another thread is complete before we free the struct, we require the RELEASE semantics of clear_bit_unlock(). This allows the conditional locking such as Thread A Thread B mutex_lock(mm_lock); if (drm_mm_node_allocated(node)) { drm_mm_node_remove(node); mutex_lock(mm_lock); mutex_unlock(mm_lock); if (drm_mm_node_allocated(node)) drm_mm_node_remove(node); mutex_unlock(mm_lock); } kfree(node); to serialise correctly without any lingering accesses from A to the freed node. Allocation / insertion of the node is assumed never to race with removal or eviction scanning. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20191003210100.22250-5-chris@chris-wilson.co.uk
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