The stop_machine() lock may allocate memory, but is called inside
vm->mutex, which is taken in the shrinker. This will cause a lockdep
splat, as can be seen below:

<4>[  462.585762] ======================================================
<4>[  462.585768] WARNING: possible circular locking dependency detected
<4>[  462.585773] 5.12.0-rc5-CI-Trybot_7644+ #1 Tainted: G     U
<4>[  462.585779] ------------------------------------------------------
<4>[  462.585783] i915_selftest/5540 is trying to acquire lock:
<4>[  462.585788] ffffffff826440b0 (cpu_hotplug_lock){++++}-{0:0}, at: stop_machine+0x12/0x30
<4>[  462.585814]
                  but task is already holding lock:
<4>[  462.585818] ffff888125369c70 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x38e/0xb40 [i915]
<4>[  462.586301]
                  which lock already depends on the new lock.

<4>[  462.586305]
                  the existing dependency chain (in reverse order) is:
<4>[  462.586309]
                  -> #2 (&vm->mutex/1){+.+.}-{3:3}:
<4>[  462.586323]        i915_gem_shrinker_taints_mutex+0x2d/0x50 [i915]
<4>[  462.586719]        i915_address_space_init+0x12d/0x130 [i915]
<4>[  462.587092]        ppgtt_init+0x4e/0x80 [i915]
<4>[  462.587467]        gen8_ppgtt_create+0x3e/0x5c0 [i915]
<4>[  462.587828]        i915_ppgtt_create+0x28/0xf0 [i915]
<4>[  462.588203]        intel_gt_init+0x123/0x370 [i915]
<4>[  462.588572]        i915_gem_init+0x129/0x1f0 [i915]
<4>[  462.588971]        i915_driver_probe+0x753/0xd80 [i915]
<4>[  462.589320]        i915_pci_probe+0x43/0x1d0 [i915]
<4>[  462.589671]        pci_device_probe+0x9e/0x110
<4>[  462.589680]        really_probe+0xea/0x410
<4>[  462.589690]        driver_probe_device+0xd9/0x140
<4>[  462.589697]        device_driver_attach+0x4a/0x50
<4>[  462.589704]        __driver_attach+0x83/0x140
<4>[  462.589711]        bus_for_each_dev+0x75/0xc0
<4>[  462.589718]        bus_add_driver+0x14b/0x1f0
<4>[  462.589724]        driver_register+0x66/0xb0
<4>[  462.589731]        i915_init+0x70/0x87 [i915]
<4>[  462.590053]        do_one_initcall+0x56/0x2e0
<4>[  462.590061]        do_init_module+0x55/0x200
<4>[  462.590068]        load_module+0x2703/0x2990
<4>[  462.590074]        __do_sys_finit_module+0xad/0x110
<4>[  462.590080]        do_syscall_64+0x33/0x80
<4>[  462.590089]        entry_SYSCALL_64_after_hwframe+0x44/0xae
<4>[  462.590096]
                  -> #1 (fs_reclaim){+.+.}-{0:0}:
<4>[  462.590109]        fs_reclaim_acquire+0x9f/0xd0
<4>[  462.590118]        kmem_cache_alloc_trace+0x3d/0x430
<4>[  462.590126]        intel_cpuc_prepare+0x3b/0x1b0
<4>[  462.590133]        cpuhp_invoke_callback+0x9e/0x890
<4>[  462.590141]        _cpu_up+0xa4/0x130
<4>[  462.590147]        cpu_up+0x82/0x90
<4>[  462.590153]        bringup_nonboot_cpus+0x4a/0x60
<4>[  462.590159]        smp_init+0x21/0x5c
<4>[  462.590167]        kernel_init_freeable+0x8a/0x1b7
<4>[  462.590175]        kernel_init+0x5/0xff
<4>[  462.590181]        ret_from_fork+0x22/0x30
<4>[  462.590187]
                  -> #0 (cpu_hotplug_lock){++++}-{0:0}:
<4>[  462.590199]        __lock_acquire+0x1520/0x2590
<4>[  462.590207]        lock_acquire+0xd1/0x3d0
<4>[  462.590213]        cpus_read_lock+0x39/0xc0
<4>[  462.590219]        stop_machine+0x12/0x30
<4>[  462.590226]        bxt_vtd_ggtt_insert_entries__BKL+0x36/0x50 [i915]
<4>[  462.590601]        ggtt_bind_vma+0x5d/0x80 [i915]
<4>[  462.590970]        i915_vma_bind+0xdc/0x1c0 [i915]
<4>[  462.591374]        i915_vma_pin_ww+0x435/0xb40 [i915]
<4>[  462.591779]        make_obj_busy+0xcb/0x330 [i915]
<4>[  462.592170]        igt_mmap_offset_exhaustion+0x45f/0x4c0 [i915]
<4>[  462.592562]        __i915_subtests.cold.7+0x42/0x92 [i915]
<4>[  462.592995]        __run_selftests.part.3+0x10d/0x172 [i915]
<4>[  462.593428]        i915_live_selftests.cold.5+0x1f/0x47 [i915]
<4>[  462.593860]        i915_pci_probe+0x93/0x1d0 [i915]
<4>[  462.594210]        pci_device_probe+0x9e/0x110
<4>[  462.594217]        really_probe+0xea/0x410
<4>[  462.594226]        driver_probe_device+0xd9/0x140
<4>[  462.594233]        device_driver_attach+0x4a/0x50
<4>[  462.594240]        __driver_attach+0x83/0x140
<4>[  462.594247]        bus_for_each_dev+0x75/0xc0
<4>[  462.594254]        bus_add_driver+0x14b/0x1f0
<4>[  462.594260]        driver_register+0x66/0xb0
<4>[  462.594267]        i915_init+0x70/0x87 [i915]
<4>[  462.594586]        do_one_initcall+0x56/0x2e0
<4>[  462.594592]        do_init_module+0x55/0x200
<4>[  462.594599]        load_module+0x2703/0x2990
<4>[  462.594605]        __do_sys_finit_module+0xad/0x110
<4>[  462.594612]        do_syscall_64+0x33/0x80
<4>[  462.594618]        entry_SYSCALL_64_after_hwframe+0x44/0xae
<4>[  462.594625]
                  other info that might help us debug this:

<4>[  462.594629] Chain exists of:
                    cpu_hotplug_lock --> fs_reclaim --> &vm->mutex/1

<4>[  462.594645]  Possible unsafe locking scenario:

<4>[  462.594648]        CPU0                    CPU1
<4>[  462.594652]        ----                    ----
<4>[  462.594655]   lock(&vm->mutex/1);
<4>[  462.594664]                                lock(fs_reclaim);
<4>[  462.594671]                                lock(&vm->mutex/1);
<4>[  462.594679]   lock(cpu_hotplug_lock);
<4>[  462.594686]
                   *** DEADLOCK ***

<4>[  462.594690] 4 locks held by i915_selftest/5540:
<4>[  462.594696]  #0: ffff888100fbc240 (&dev->mutex){....}-{3:3}, at: device_driver_attach+0x18/0x50
<4>[  462.594715]  #1: ffffc900006cb9a0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: make_obj_busy+0x81/0x330 [i915]
<4>[  462.595118]  #2: ffff88812a6081e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: make_obj_busy+0x21f/0x330 [i915]
<4>[  462.595519]  #3: ffff888125369c70 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x38e/0xb40 [i915]
<4>[  462.595934]
                  stack backtrace:
<4>[  462.595939] CPU: 0 PID: 5540 Comm: i915_selftest Tainted: G     U            5.12.0-rc5-CI-Trybot_7644+ #1
<4>[  462.595947] Hardware name: GOOGLE Kefka/Kefka, BIOS MrChromebox 02/04/2018
<4>[  462.595952] Call Trace:
<4>[  462.595961]  dump_stack+0x7f/0xad
<4>[  462.595974]  check_noncircular+0x12e/0x150
<4>[  462.595982]  ? save_stack.isra.17+0x3f/0x70
<4>[  462.595991]  ? drm_mm_insert_node_in_range+0x34a/0x5b0
<4>[  462.596000]  ? i915_vma_pin_ww+0x9ec/0xb40 [i915]
<4>[  462.596410]  __lock_acquire+0x1520/0x2590
<4>[  462.596419]  ? do_init_module+0x55/0x200
<4>[  462.596429]  lock_acquire+0xd1/0x3d0
<4>[  462.596435]  ? stop_machine+0x12/0x30
<4>[  462.596445]  ? gen8_ggtt_insert_entries+0xf0/0xf0 [i915]
<4>[  462.596816]  cpus_read_lock+0x39/0xc0
<4>[  462.596824]  ? stop_machine+0x12/0x30
<4>[  462.596831]  stop_machine+0x12/0x30
<4>[  462.596839]  bxt_vtd_ggtt_insert_entries__BKL+0x36/0x50 [i915]
<4>[  462.597210]  ggtt_bind_vma+0x5d/0x80 [i915]
<4>[  462.597580]  i915_vma_bind+0xdc/0x1c0 [i915]
<4>[  462.597986]  i915_vma_pin_ww+0x435/0xb40 [i915]
<4>[  462.598395]  ? make_obj_busy+0xcb/0x330 [i915]
<4>[  462.598786]  make_obj_busy+0xcb/0x330 [i915]
<4>[  462.599180]  ? 0xffffffff81000000
<4>[  462.599187]  ? debug_mutex_unlock+0x50/0xa0
<4>[  462.599198]  igt_mmap_offset_exhaustion+0x45f/0x4c0 [i915]
<4>[  462.599592]  __i915_subtests.cold.7+0x42/0x92 [i915]
<4>[  462.600026]  ? i915_perf_selftests+0x20/0x20 [i915]
<4>[  462.600422]  ? __i915_nop_setup+0x10/0x10 [i915]
<4>[  462.600820]  __run_selftests.part.3+0x10d/0x172 [i915]
<4>[  462.601253]  i915_live_selftests.cold.5+0x1f/0x47 [i915]
<4>[  462.601686]  i915_pci_probe+0x93/0x1d0 [i915]
<4>[  462.602037]  ? _raw_spin_unlock_irqrestore+0x3d/0x60
<4>[  462.602047]  pci_device_probe+0x9e/0x110
<4>[  462.602057]  really_probe+0xea/0x410
<4>[  462.602067]  driver_probe_device+0xd9/0x140
<4>[  462.602075]  device_driver_attach+0x4a/0x50
<4>[  462.602084]  __driver_attach+0x83/0x140
<4>[  462.602091]  ? device_driver_attach+0x50/0x50
<4>[  462.602099]  ? device_driver_attach+0x50/0x50
<4>[  462.602107]  bus_for_each_dev+0x75/0xc0
<4>[  462.602116]  bus_add_driver+0x14b/0x1f0
<4>[  462.602124]  driver_register+0x66/0xb0
<4>[  462.602133]  i915_init+0x70/0x87 [i915]
<4>[  462.602453]  ? 0xffffffffa0606000
<4>[  462.602458]  do_one_initcall+0x56/0x2e0
<4>[  462.602466]  ? kmem_cache_alloc_trace+0x374/0x430
<4>[  462.602476]  do_init_module+0x55/0x200
<4>[  462.602484]  load_module+0x2703/0x2990
<4>[  462.602500]  ? __do_sys_finit_module+0xad/0x110
<4>[  462.602507]  __do_sys_finit_module+0xad/0x110
<4>[  462.602519]  do_syscall_64+0x33/0x80
<4>[  462.602527]  entry_SYSCALL_64_after_hwframe+0x44/0xae
<4>[  462.602535] RIP: 0033:0x7fab69d8d89d

Changes since v1:
- Add lockdep annotations during init, to ensure that lockdep is primed.
  This also fixes a false positive when reading /proc/lockdep_stats
  during module reload.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210426102351.921874-1-maarten.lankhorst@linux.intel.comReviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>