drm/i915: Avoid reclaim taints from runtime-pm debug

As intel_runtime_pm_get/_put may be called from any blockable context,
we need to avoid allowing reclaim from our mallocs, as we need to
avoid tainting any mutexes held by the callers (as they may themselves
not allow for allocations as they are taken in the shrinker).

<4> [435.339331] WARNING: possible circular locking dependency detected
<4> [435.339364] 5.1.0-rc4-CI-Trybot_4116+ #1 Tainted: G     U
<4> [435.339395] ------------------------------------------------------
<4> [435.339426] gem_caching/1334 is trying to acquire lock:
<4> [435.339456] 000000004505c39b (wakeref#3){+.+.}, at: intel_engine_pm_put+0x1b/0x40 [i915]
<4> [435.339788]
but task is already holding lock:
<4> [435.339819] 00000000ee77b4ed (fs_reclaim){+.+.}, at: fs_reclaim_acquire.part.24+0x0/0x30
<4> [435.339879]
which lock already depends on the new lock.

<4> [435.339918]
the existing dependency chain (in reverse order) is:
<4> [435.339952]
-> #1 (fs_reclaim){+.+.}:
<4> [435.339998]        fs_reclaim_acquire.part.24+0x24/0x30
<4> [435.340035]        kmem_cache_alloc_trace+0x2a/0x290
<4> [435.340311]        __print_intel_runtime_pm_wakeref+0x24/0x160 [i915]
<4> [435.340590]        untrack_intel_runtime_pm_wakeref+0x16e/0x1d0 [i915]
<4> [435.340869]        intel_runtime_pm_put_unchecked+0xd/0x30 [i915]
<4> [435.341147]        __intel_wakeref_put_once+0x22/0x40 [i915]
<4> [435.341508]        i915_request_retire+0x477/0xaf0 [i915]
<4> [435.341871]        ring_retire_requests+0x86/0x160 [i915]
<4> [435.342226]        i915_retire_requests+0x58/0xc0 [i915]
<4> [435.342576]        retire_work_handler+0x5b/0x70 [i915]
<4> [435.342615]        process_one_work+0x245/0x610
<4> [435.342646]        worker_thread+0x37/0x380
<4> [435.342679]        kthread+0x119/0x130
<4> [435.342714]        ret_from_fork+0x3a/0x50
<4> [435.342739]
-> #0 (wakeref#3){+.+.}:
<4> [435.342788]        lock_acquire+0xa6/0x1c0
<4> [435.342822]        __mutex_lock+0x8c/0x960
<4> [435.342853]        atomic_dec_and_mutex_lock+0x33/0x50
<4> [435.343151]        intel_engine_pm_put+0x1b/0x40 [i915]
<4> [435.343501]        i915_request_retire+0x477/0xaf0 [i915]
<4> [435.343851]        ring_retire_requests+0x86/0x160 [i915]
<4> [435.344202]        i915_retire_requests+0x58/0xc0 [i915]
<4> [435.344543]        i915_gem_shrink+0xd8/0x5b0 [i915]
<4> [435.344835]        i915_drop_caches_set+0x17b/0x250 [i915]
<4> [435.344877]        simple_attr_write+0xb0/0xd0
<4> [435.344911]        full_proxy_write+0x51/0x80
<4> [435.344943]        vfs_write+0xbd/0x1b0
<4> [435.344972]        ksys_write+0x55/0xe0
<4> [435.345002]        do_syscall_64+0x55/0x190
<4> [435.345040]        entry_SYSCALL_64_after_hwframe+0x49/0xbe

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190409174108.19396-1-chris@chris-wilson.co.uk