Re: [PATCH v5] drm/virtio: Add drm_panic support

[Dmitry Osipenko]

On 12/2/24 20:19, Jocelyn Falempe wrote:
>>>
>>> I've now noticed that drm_gem_shmem_vmap() expects BO reservation lock
>>> to be held and we can't take lock it at a panic time.
>>>
>>> https://elixir.bootlin.com/linux/v6.12.1/source/drivers/gpu/drm/
>>> drm_gem_shmem_helper.c#L330
>>>
>>> This resv warning isn't triggered because bo->base.vaddr is set for VT
>>> framebufffer BO when panic happens.
> 
> I usually test using gnome desktop in the VM, and in this case vaddr is
> not set, and calling vmap() is needed. (and I don't get the warning, I
> will check why).

All those get_pages() and vmap() that drm_gem_shmem_vmap() uses may
sleep. You'll need to add atomic variants for the vmap funcs if it's
really needed.

Like I said in the comment to v6, let's start with rejecting BOs that
aren't vmapped. If atomic vmap will become needed, it will be a separate
problem to solve.

-- 
Best regards,
Dmitry