drm/i915: Only mark the execobject as pinned on success

If we fail to acquire a fence (for old school fenced GPU access) then we
unwind the vma reservation, including its pin. However, we were making
the execobject as holding the pin before erring out, leading to a double
unpin:

[ 3193.991802] kernel BUG at drivers/gpu/drm/i915/i915_vma.h:287!
[ 3193.998131] invalid opcode: 0000 [#1] PREEMPT SMP
[ 3194.002816] Modules linked in: snd_hda_intel i915 vgem snd_hda_codec_analog snd_hda_codec_generic coretemp snd_hda_codec snd_hwdep snd_hda_core snd_pcm lpc_ich mei_me e1000e mei prime_numbers ptp pps_core [last unloaded: i915]
[ 3194.022841] CPU: 0 PID: 8123 Comm: kms_flip Tainted: G     U          4.13.0-rc1-CI-CI_DRM_471+ #1
[ 3194.031765] Hardware name: Dell Inc. OptiPlex 755                 /0PU052, BIOS A04 11/05/2007
[ 3194.040343] task: ffff8800785d4c40 task.stack: ffffc90001768000
[ 3194.046339] RIP: 0010:eb_release_vmas.isra.6+0x119/0x180 [i915]
[ 3194.052234] RSP: 0018:ffffc9000176ba80 EFLAGS: 00010246
[ 3194.057439] RAX: 00000000000003c0 RBX: ffff8800710fc2d8 RCX: ffff8800588e4f48
[ 3194.064546] RDX: ffffffff1fffffff RSI: 00000000ffffffff RDI: ffff8800588e00d0
[ 3194.071654] RBP: ffffc9000176bab0 R08: 0000000000000000 R09: 0000000000000000
[ 3194.078761] R10: 0000000000000040 R11: 0000000000000001 R12: ffff880060822f00
[ 3194.085867] R13: 0000000000000310 R14: 00000000000003b8 R15: ffffc9000176bbb0
[ 3194.092975] FS:  00007fd2b94aba40(0000) GS:ffff88007d200000(0000) knlGS:0000000000000000
[ 3194.101033] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3194.106754] CR2: 00007ffbec3ff000 CR3: 0000000074e67000 CR4: 00000000000006f0
[ 3194.113861] Call Trace:
[ 3194.116321]  eb_relocate_slow+0x67/0x4e0 [i915]
[ 3194.120861]  i915_gem_do_execbuffer+0x429/0x1260 [i915]
[ 3194.126070]  ? lock_acquire+0xb5/0x210
[ 3194.129803]  ? __might_fault+0x39/0x90
[ 3194.133563]  i915_gem_execbuffer2+0x9b/0x1b0 [i915]
[ 3194.138447]  ? i915_gem_execbuffer+0x2b0/0x2b0 [i915]
[ 3194.143478]  drm_ioctl_kernel+0x64/0xb0
[ 3194.147298]  drm_ioctl+0x2cd/0x390
[ 3194.150710]  ? i915_gem_execbuffer+0x2b0/0x2b0 [i915]
[ 3194.155741]  ? finish_task_switch+0xa5/0x210
[ 3194.159993]  ? finish_task_switch+0x6a/0x210
[ 3194.164247]  do_vfs_ioctl+0x90/0x670
[ 3194.167806]  ? entry_SYSCALL_64_fastpath+0x5/0xb1
[ 3194.172492]  ? __this_cpu_preempt_check+0x13/0x20
[ 3194.177176]  ? trace_hardirqs_on_caller+0xe7/0x1c0
[ 3194.181946]  SyS_ioctl+0x3c/0x70
[ 3194.185159]  entry_SYSCALL_64_fastpath+0x1c/0xb1
[ 3194.189756] RIP: 0033:0x7fd2b76a8587
[ 3194.193314] RSP: 002b:00007fff074845b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[ 3194.200855] RAX: ffffffffffffffda RBX: ffffffff8146da43 RCX: 00007fd2b76a8587
[ 3194.207962] RDX: 00007fff074846e0 RSI: 0000000040406469 RDI: 0000000000000003
[ 3194.215068] RBP: ffffc9000176bf88 R08: 0000000000000000 R09: 0000000000000003
[ 3194.222175] R10: 00007fd2b796bb58 R11: 0000000000000246 R12: 00007fff07484880
[ 3194.229280] R13: 0000000000000003 R14: 0000000040406469 R15: 0000000000000000
[ 3194.236386]  ? __this_cpu_preempt_check+0x13/0x20
[ 3194.241070] Code: 24 b0 00 00 00 48 85 c9 0f 84 6c ff ff ff 8b 41 20 85 c0 7e 73 83 e8 01 89 41 20 41 8b 84 24 e8 00 00 00 a8 0f 0f 85 5f ff ff ff <0f> 0b 48 83 c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d f3 c3 49 8b 84
[ 3194.259943] RIP: eb_release_vmas.isra.6+0x119/0x180 [i915] RSP: ffffc9000176ba80
[ 3194.268047] ---[ end trace 1d7348c6575d8800 ]---
[ 3673.658819] softdog: Initiating panic
[ 3673.662471] Kernel panic - not syncing: Software Watchdog Timer expired
[ 3673.669066] Kernel Offset: disabled
[ 3673.672541] Rebooting in 1 seconds..

Reported-by: Tomi Sarvela <tomi.p.sarvela@intel.com>
Fixes: 2889caa92321 ("drm/i915: Eliminate lots of iterations over the execobjects array")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170721145037.25105-3-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -560,9 +560,6 @@ static int eb_reserve_vma(const struct i915_execbuffer *eb,
 		eb->args->flags |= __EXEC_HAS_RELOC;
 	}
 
-	entry->flags |= __EXEC_OBJECT_HAS_PIN;
-	GEM_BUG_ON(eb_vma_misplaced(entry, vma));
-
 	if (unlikely(entry->flags & EXEC_OBJECT_NEEDS_FENCE)) {
 		err = i915_vma_get_fence(vma);
 		if (unlikely(err)) {
@@ -574,6 +571,9 @@ static int eb_reserve_vma(const struct i915_execbuffer *eb,
 			entry->flags |= __EXEC_OBJECT_HAS_FENCE;
 	}
 
+	entry->flags |= __EXEC_OBJECT_HAS_PIN;
+	GEM_BUG_ON(eb_vma_misplaced(entry, vma));
+
 	return 0;
 }