drm/panfrost: Fix dma_resv deadlock at drm object pin time

When Panfrost must pin an object that is being prepared a dma-buf
attachment for on behalf of another driver, the core drm gem object pinning
code already takes a lock on the object's dma reservation.

However, Panfrost GEM object's pinning callback would eventually try taking
the lock on the same dma reservation when delegating pinning of the object
onto the shmem subsystem, which led to a deadlock.

This can be shown by enabling CONFIG_DEBUG_WW_MUTEX_SLOWPATH, which throws
the following recursive locking situation:

weston/3440 is trying to acquire lock:
ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_shmem_pin+0x34/0xb8 [drm_shmem_helper]
but task is already holding lock:
ffff000000e235a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_gem_pin+0x2c/0x80 [drm]

Fix it by replacing drm_gem_shmem_pin with its locked version, as the lock
had already been taken by drm_gem_pin().

Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Steven Price <steven.price@arm.com>
Fixes: a78027847226 ("drm/gem: Acquire reservation lock in drm_gem_{pin/unpin}()")
Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240523113236.432585-2-adrian.larumbe@collabora.com

diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
index d47b40b82b0bc4d189a2fa6772aaf3a91ee54c18..8e0ff3efede7e3206b75d38328dc843b741ce022 100644 (file)
--- a/drivers/gpu/drm/panfrost/panfrost_gem.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
@@ -192,7 +192,7 @@ static int panfrost_gem_pin(struct drm_gem_object *obj)
        if (bo->is_heap)
                return -EINVAL;
 
-       return drm_gem_shmem_pin(&bo->base);
+       return drm_gem_shmem_pin_locked(&bo->base);
 }
 
 static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_object *obj)