Re: [PATCH v3 0/2] drm: Fix dma_resv deadlock at drm object pin time

[Boris Brezillon]

Hi Thomas,

On Thu, 2 May 2024 13:51:16 +0200
Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:

> Hi,
> 
> ignoring my r-b on patch 1, I'd like to rethink the current patches in 
> general.
> 
> I think drm_gem_shmem_pin() should become the locked version of _pin(), 
> so that drm_gem_shmem_object_pin() can call it directly. The existing 
> _pin_unlocked() would not be needed any longer. Same for the _unpin() 
> functions. This change would also fix the consistency with the semantics 
> of the shmem _vmap() functions, which never take reservation locks.
> 
> There are only two external callers of drm_gem_shmem_pin(): the test 
> case and panthor. These assume that drm_gem_shmem_pin() acquires the 
> reservation lock. The test case should likely call drm_gem_pin() 
> instead. That would acquire the reservation lock and the test would 
> validate that shmem's pin helper integrates well into the overall GEM 
> framework. The way panthor uses drm_gem_shmem_pin() looks wrong to me. 
> For now, it could receive a wrapper that takes the lock and that's it.

I do agree that the current inconsistencies in the naming is
troublesome (sometimes _unlocked, sometimes _locked, with the version
without any suffix meaning either _locked or _unlocked depending on
what the suffixed version does), and that's the very reason I asked
Dmitry to address that in his shrinker series [1]. So, ideally I'd
prefer if patches from Dmitry's series were applied instead of
trying to fix that here (IIRC, we had an ack from Maxime).

Regards,

Boris