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

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Date: Thu, 2 May 2024 13:51:16 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Adrián Larumbe <adrian.larumbe@...labora.com>,
 Qiang Yu <yuq825@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>,
 Boris Brezillon <boris.brezillon@...labora.com>,
 Rob Herring <robh@...nel.org>, Steven Price <steven.price@....com>,
 Sumit Semwal <sumit.semwal@...aro.org>,
 Christian Koenig= <christian.koenig@....com>,
 Dmitry Osipenko <dmitry.osipenko@...labora.com>,
 Zack Rusin <zack.rusin@...adcom.com>
Cc: kernel@...labora.com, dri-devel@...ts.freedesktop.org,
 lima@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v3 0/2] drm: Fix dma_resv deadlock at drm object pin time

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.

Best regards
Thomas

Am 01.05.24 um 08:55 schrieb Adrián Larumbe:
> This is v3 of https://lore.kernel.org/dri-devel/20240424090429.57de7d1c@collabora.com/
>
> The goal of this patch series is fixing a deadlock upon locking the dma reservation
> of a DRM gem object when pinning it, at a prime import operation.
>
> Changes from v2:
>   - Removed comment explaining reason why an already-locked
> pin function replaced the locked variant inside Panfrost's
> object pin callback.
>   - Moved already-assigned attachment warning into generic
> already-locked gem object pin function
>
> Adrián Larumbe (2):
>    drm/panfrost: Fix dma_resv deadlock at drm object pin time
>    drm/gem-shmem: Add import attachment warning to locked pin function
>
>   drivers/gpu/drm/drm_gem_shmem_helper.c  | 2 ++
>   drivers/gpu/drm/lima/lima_gem.c         | 2 +-
>   drivers/gpu/drm/panfrost/panfrost_gem.c | 2 +-
>   3 files changed, 4 insertions(+), 2 deletions(-)
>
>
> base-commit: 75b68f22e39aafb22f3d8e3071e1aba73560788c

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)