drm/nouveau: Add a dedicated mutex for the clients list

mainline inclusion
from mainline
commit abae9164
bugzilla: 185776 https://gitee.com/openeuler/kernel/issues/I4DDEL
CVE: CVE-2020-27820

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=abae9164a421bc4a41a3769f01ebcd1f9d955e0e



--------------------------------

Rather than protecting the nouveau_drm clients list with the lock within
the "client" nouveau_cli, add a dedicated lock to serialize access to
the list. This is both clearer and necessary to avoid lockdep being
upset with us when we need to iterate through all the clients in the
list and potentially lock their mutex, which is the same class as the
lock protecting the entire list.

Cc: stable@vger.kernel.org # 5.4+
Signed-off-by: Jeremy Cline <jcline@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Tested-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201125202648.5220-3-jcline@redhat.com
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/14


Signed-off-by: Chen Jun <chenjun102@huawei.com>
Reviewed-by: weiyang wang <wangweiyang2@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>