Re: [PATCH 28/46] mm/mmu_notifier: set ->mm only after mmgrab()

[Gregory Price]

On 2026-10-27 00:17 +0100, David Hildenbrand (Arm) wrote:
> From: Chris Mason <mason@xxxxxxxxxx>
> 
> Radeon uses a non-NULL notifier->mm to decide whether to call
> mmu_interval_notifier_remove() when freeing a buffer object.
> __mmu_interval_notifier_insert() sets ->mm before validating the range,
> so a wrapping userptr range can leave ->mm set after insertion fails.
> Cleanup then tries to remove an unregistered notifier for which no mm
> reference was acquired.
> 
> Set ->mm only after mmgrab(), once insertion can no longer fail. While
> we could fix radeon's code instead, setting ->mm on success only makes
> the code more robust.
> 
> Fix generated by an LLM and sent by Chris Mason in private.
> 
> Fixes: 3506ff69c3ec ("drm/radeon: use mmu_interval_notifier_insert")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Chris Mason <mason@xxxxxxxxxx>
> [ david: simplify description ]
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
Tested-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>

-- 
Gregory Price <gourry@xxxxxxxxxx>