drm/i915/gem: Wait on unbind barriers when invalidating userptr

drm/i915/gem: Wait on unbind barriers when invalidating userptr

When we are told we have to drop all references to userptr, wait for any
barriers required for unbinding.

<4> [2055.808787] WARNING: CPU: 3 PID: 6239 at mm/mmu_notifier.c:472 __mmu_notifier_invalidate_range_start+0x1f2/0x250
<4> [2055.808792] Modules linked in: vgem mei_hdcp snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic x86_pkg_temp_thermal coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel r8169 lpc_ich realtek i915 snd_hda_intel snd_intel_dspcfg snd_hda_codec snd_hwdep snd_hda_core pinctrl_broxton snd_pcm pinctrl_intel mei_me intel_lpss_pci mei prime_numbers [last unloaded: vgem]
<4> [2055.808834] CPU: 3 PID: 6239 Comm: gem_userptr_bli Tainted: G     U            5.5.0-rc1-CI-CI_DRM_7522+ #1
<4> [2055.808839] Hardware name:  /NUC6CAYB, BIOS AYAPLCEL.86A.0049.2018.0508.1356 05/08/2018
<4> [2055.808847] RIP: 0010:__mmu_notifier_invalidate_range_start+0x1f2/0x250
<4> [2055.808853] Code: c2 48 c7 c7 70 17 2e 82 44 89 45 d4 48 8b 70 28 e8 ec 01 ef ff 41 f6 46 20 01 44 8b 45 d4 75 0a 41 83 f8 f5 44 89 7d d4 74 89 <0f> 0b 44 89 45 d4 eb 81 0f 0b 49 8b 46 18 49 8b 76 10 4c 89 ff 48
<4> [2055.808858] RSP: 0018:ffffc90002937d40 EFLAGS: 00010202
<4> [2055.808865] RAX: 0000000000000061 RBX: ffff8882703a33e0 RCX: 0000000000000001
<4> [2055.808870] RDX: 0000000000000000 RSI: ffff888277da8cb8 RDI: 00000000ffffffff
<4> [2055.808874] RBP: ffffc90002937d70 R08: 00000000fffffff5 R09: 0000000000000000
<4> [2055.808879] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
<4> [2055.808884] R13: ffffffff822e1716 R14: ffffc90002937d80 R15: 00000000fffffff5
<4> [2055.808890] FS:  00007fda75004e40(0000) GS:ffff888277d80000(0000) knlGS:0000000000000000
<4> [2055.808895] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4> [2055.808900] CR2: 000055ad72ec3000 CR3: 00000002697b2000 CR4: 00000000003406e0
<4> [2055.808904] Call Trace:
<4> [2055.808920]  unmap_vmas+0x13e/0x150
<4> [2055.808937]  unmap_region+0xa3/0x100
<4> [2055.808964]  __do_munmap+0x26d/0x490
<4> [2055.808980]  __vm_munmap+0x66/0xc0
<4> [2055.808994]  __x64_sys_munmap+0x12/0x20
<4> [2055.809001]  do_syscall_64+0x4f/0x220

Closes: https://gitlab.freedesktop.org/drm/intel/issues/771
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191210133719.3874455-1-chris@chris-wilson.co.uk