drm/i915: Use static allocation for i915_globals_park()

drm/i915: Use static allocation for i915_globals_park()

In order to avoid the malloc inside i915_globals_park() occurring
underneath a lock connected to the shrinker (thus causing circular
lockdeps warnings), move the rcu_worker to a global.

<4> [39.085073] ======================================================
<4> [39.085273] WARNING: possible circular locking dependency detected
<4> [39.085552] 5.1.0-rc3-CI-Trybot_4088+ #1 Tainted: G     U
<4> [39.085752] ------------------------------------------------------
<4> [39.085949] kswapd0/32 is trying to acquire lock:
<4> [39.086121] 00000000004b5f91 (wakeref#3){+.+.}, at: intel_engine_pm_put+0x1b/0x40 [i915]
<4> [39.086493]
but task is already holding lock:
<4> [39.086682] 00000000dd009a9a (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30
<4> [39.086910]
which lock already depends on the new lock.

<4> [39.087139]
the existing dependency chain (in reverse order) is:
<4> [39.087356]
-> #2 (fs_reclaim){+.+.}:
<4> [39.087604]        fs_reclaim_acquire.part.24+0x24/0x30
<4> [39.087785]        kmem_cache_alloc_trace+0x2a/0x290
<4> [39.087998]        i915_globals_park+0x22/0xa0 [i915]
<4> [39.088478]        idle_work_handler+0x1df/0x220 [i915]
<4> [39.089016]        process_one_work+0x245/0x610
<4> [39.089447]        worker_thread+0x37/0x380
<4> [39.089956]        kthread+0x119/0x130
<4> [39.090374]        ret_from_fork+0x3a/0x50
<4> [39.090868]
-> #1 (wakeref#4){+.+.}:
<4> [39.091569]        __mutex_lock+0x8c/0x960
<4> [39.092054]        atomic_dec_and_mutex_lock+0x33/0x50
<4> [39.092521]        intel_gt_pm_put+0x1b/0x40 [i915]
<4> [39.093047]        intel_engine_park+0xeb/0x1d0 [i915]
<4> [39.093514]        __intel_wakeref_put_once+0x10/0x30 [i915]
<4> [39.094062]        i915_request_retire+0x477/0xaf0 [i915]
<4> [39.094547]        ring_retire_requests+0x86/0x160 [i915]
<4> [39.095110]        i915_retire_requests+0x58/0xc0 [i915]
<4> [39.095587]        i915_gem_wait_for_idle.part.22+0xb2/0xf0 [i915]
<4> [39.096142]        switch_to_kernel_context_sync+0x2a/0x70 [i915]
<4> [39.096633]        i915_gem_init+0x59c/0x9c0 [i915]
<4> [39.097174]        i915_driver_load+0xd96/0x1880 [i915]
<4> [39.097640]        i915_pci_probe+0x29/0xa0 [i915]
<4> [39.098145]        pci_device_probe+0xa1/0x120
<4> [39.098607]        really_probe+0xf3/0x3e0
<4> [39.099031]        driver_probe_device+0x10a/0x120
<4> [39.099599]        device_driver_attach+0x4b/0x50
<4> [39.100033]        __driver_attach+0x97/0x130
<4> [39.100525]        bus_for_each_dev+0x74/0xc0
<4> [39.100954]        bus_add_driver+0x13f/0x210
<4> [39.101441]        driver_register+0x56/0xe0
<4> [39.101891]        do_one_initcall+0x58/0x2e0
<4> [39.102319]        do_init_module+0x56/0x1ea
<4> [39.102805]        load_module+0x2701/0x29e0
<4> [39.103231]        __se_sys_finit_module+0xd3/0xf0
<4> [39.103727]        do_syscall_64+0x55/0x190
<4> [39.104153]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4> [39.104736]
-> #0 (wakeref#3){+.+.}:
<4> [39.105437]        lock_acquire+0xa6/0x1c0
<4> [39.105923]        __mutex_lock+0x8c/0x960
<4> [39.106345]        atomic_dec_and_mutex_lock+0x33/0x50
<4> [39.106897]        intel_engine_pm_put+0x1b/0x40 [i915]
<4> [39.107375]        i915_request_retire+0x477/0xaf0 [i915]
<4> [39.107930]        ring_retire_requests+0x86/0x160 [i915]
<4> [39.108412]        i915_retire_requests+0x58/0xc0 [i915]
<4> [39.108934]        i915_gem_shrink+0xd8/0x5b0 [i915]
<4> [39.109431]        i915_gem_shrinker_scan+0x59/0x130 [i915]
<4> [39.109884]        do_shrink_slab+0x131/0x3e0
<4> [39.110380]        shrink_slab+0x228/0x2c0
<4> [39.110810]        shrink_node+0x177/0x460
<4> [39.111317]        balance_pgdat+0x239/0x580
<4> [39.111743]        kswapd+0x186/0x570
<4> [39.112221]        kthread+0x119/0x130
<4> [39.112641]        ret_from_fork+0x3a/0x50

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/20190408091728.20207-3-chris@chris-wilson.co.uk