__i915_guc_submit may be, despite my assertion, called from outside of
an irq-safe spinlock so we need to use a full spin_lock_irqsave and not
cheat using a spin_lock. (The initial notify callback from the completed
fence is called before the spinlock is taken to wake up all waiters and
call their callbacks.)

[   48.166581] kernel BUG at drivers/gpu/drm/i915/i915_guc_submission.c:527!
[   48.166617] invalid opcode: 0000 [#1] PREEMPT SMP
[   48.166644] Modules linked in: i915 prime_numbers x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel mei_me mei i2c_i801 netconsole i2c_hid [last unloaded: i915]
[   48.166733] CPU: 2 PID: 5 Comm: kworker/u8:0 Tainted: G     U          4.10.0nightly-170302-guc_scrub+ #19
[   48.166778] Hardware name:                  /NUC6i5SYB, BIOS SYSKLi35.86A.0054.2016.0930.1102 09/30/2016
[   48.166835] Workqueue: i915 __intel_autoenable_gt_powersave [i915]
[   48.166865] task: ffff88084ab7cf40 task.stack: ffffc90000064000
[   48.166921] RIP: 0010:__i915_guc_submit+0x1e6/0x2a0 [i915]
[   48.166953] RSP: 0018:ffffc90000067c80 EFLAGS: 00010202
[   48.166979] RAX: 0000000000000202 RBX: ffff8808465e0c68 RCX: 0000000000000201
[   48.167016] RDX: 0000000080000201 RSI: ffff88084ab7d798 RDI: ffff88082b8a8040
[   48.167054] RBP: ffffc90000067cd8 R08: 0000000000000001 R09: 0000000000000000
[   48.167085] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88082b8a8148
[   48.167126] R13: 0000000000000000 R14: ffff88082f440000 R15: ffff88082e85e660
[   48.167156] FS:  0000000000000000(0000) GS:ffff88086ed00000(0000) knlGS:0000000000000000
[   48.167195] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   48.167226] CR2: 000055862ffcdc2c CR3: 0000000001e0f000 CR4: 00000000003406e0
[   48.167257] Call Trace:
[   48.168112]  ? trace_hardirqs_on+0xd/0x10
[   48.168966]  ? _raw_spin_unlock_irqrestore+0x4a/0x80
[   48.169831]  i915_guc_submit+0x1a/0x20 [i915]
[   48.170680]  submit_notify+0x89/0xc0 [i915]
[   48.171512]  __i915_sw_fence_complete+0x175/0x220 [i915]
[   48.172340]  i915_sw_fence_complete+0x2a/0x50 [i915]
[   48.173158]  i915_sw_fence_commit+0x21/0x30 [i915]
[   48.173968]  __i915_add_request+0x238/0x530 [i915]
[   48.174764]  __intel_autoenable_gt_powersave+0x8b/0xb0 [i915]
[   48.175549]  process_one_work+0x218/0x690
[   48.176318]  ? process_one_work+0x197/0x690
[   48.177183]  worker_thread+0x4e/0x4a0
[   48.178039]  kthread+0x10c/0x140
[   48.178878]  ? process_one_work+0x690/0x690
[   48.179718]  ? kthread_create_on_node+0x40/0x40
[   48.180568]  ret_from_fork+0x31/0x40
[   48.181423] Code: 02 00 00 43 89 84 ae 50 11 00 00 e8 75 01 62 e1 48 83 c4 30 5b 41 5c 41 5d 41 5e 41 5f 5d c3 48 c1 e0 20 48 09 c2 49 89 d0 eb 82 <0f> 0b 0f 0b 0f 0b 0f 0b 0f 0b 0f 0b 49 c1 e8 20 44 89 43 34 4a
[   48.183336] RIP: __i915_guc_submit+0x1e6/0x2a0 [i915] RSP: ffffc90000067c80
Reported-by: NArkadiusz Hiler <arkadiusz.hiler@intel.com>
Fixes: 349ab919 ("drm/i915/guc: Make wq_lock irq-safe")
Fixes: 67b807a8 ("drm/i915: Delay disabling the user interrupt for breadcrumbs")
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170302145323.12886-1-chris@chris-wilson.co.ukReviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NArkadiusz Hiler <arkadiusz.hiler@intel.com>
Tested-by: NArkadiusz Hiler <arkadiusz.hiler@intel.com>