Acquire the buffer object's reservation lock in drm_gem_pin() and
remove locking the drivers' GEM callbacks where necessary. Same for
unpin().

DRM drivers and memory managers modified by this patch will now have
correct dma-buf locking semantics: the caller is responsible for
holding the reservation lock when calling the pin or unpin callback.

DRM drivers and memory managers that are not modified will now be
protected against concurent invocation of their pin and unpin callbacks.

PRIME does not implement struct dma_buf_ops.pin, which requires
the caller to hold the reservation lock. It does implement struct
dma_buf_ops.attach, which requires to callee to acquire the
reservation lock. The PRIME code uses drm_gem_pin(), so locks
are now taken as specified. Same for unpin and detach.

The patch harmonizes GEM pin and unpin to have non-interruptible
reservation locking across all drivers, as is already the case for
vmap and vunmap. This affects gem-shmem, gem-vram, loongson, qxl and
radeon.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> # virtio-gpu
Link: https://patchwork.freedesktop.org/patch/msgid/20240227113853.8464-10-tzimmermann@suse.de