Commit bc6f80cc authored Apr 26, 2021 by Maarten Lankhorst

drm/i915: Use trylock in shrinker for ggtt on bsw vt-d and bxt, v2.



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.com


Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

parent ff2d0ba2

drivers/gpu/drm/i915/gem/i915_gem_shrinker.c

+9 −4

Original line number	Diff line number	Diff line
		@@ -38,15 +38,17 @@ static bool can_release_pages(struct drm_i915_gem_object *obj)
		}

		static bool unsafe_drop_pages(struct drm_i915_gem_object *obj,
		unsigned long shrink)
		unsigned long shrink, bool trylock_vm)
		{
		unsigned long flags;

		flags = 0;
		if (shrink & I915_SHRINK_ACTIVE)
		flags = I915_GEM_OBJECT_UNBIND_ACTIVE;
		flags \|= I915_GEM_OBJECT_UNBIND_ACTIVE;
		if (!(shrink & I915_SHRINK_BOUND))
		flags = I915_GEM_OBJECT_UNBIND_TEST;
		flags \|= I915_GEM_OBJECT_UNBIND_TEST;
		if (trylock_vm)
		flags \|= I915_GEM_OBJECT_UNBIND_VM_TRYLOCK;

		if (i915_gem_object_unbind(obj, flags) == 0)
		return true;
		@@ -117,6 +119,9 @@ i915_gem_shrink(struct i915_gem_ww_ctx *ww,
		unsigned long scanned = 0;
		int err;

		/* CHV + VTD workaround use stop_machine(); need to trylock vm->mutex */
		bool trylock_vm = !ww && intel_vm_no_concurrent_access_wa(i915);

		trace_i915_gem_shrink(i915, target, shrink);

		/*
		@@ -204,7 +209,7 @@ i915_gem_shrink(struct i915_gem_ww_ctx *ww,
		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);

		err = 0;
		if (unsafe_drop_pages(obj, shrink)) {
		if (unsafe_drop_pages(obj, shrink, trylock_vm)) {
		/* May arrive from get_pages on another bo */
		if (!ww) {
		if (!i915_gem_object_trylock(obj))

drivers/gpu/drm/i915/gt/intel_ggtt.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -906,9 +906,11 @@ static int gen8_gmch_probe(struct i915_ggtt *ggtt)

		ggtt->vm.insert_entries = gen8_ggtt_insert_entries;

		/* Serialize GTT updates with aperture access on BXT if VT-d is on. */
		if (intel_ggtt_update_needs_vtd_wa(i915) \|\|
		IS_CHERRYVIEW(i915) /* fails with concurrent use/update */) {
		/*
		* Serialize GTT updates with aperture access on BXT if VT-d is on,
		* and always on CHV.
		*/
		if (intel_vm_no_concurrent_access_wa(i915)) {
		ggtt->vm.insert_entries = bxt_vtd_ggtt_insert_entries__BKL;
		ggtt->vm.insert_page = bxt_vtd_ggtt_insert_page__BKL;
		ggtt->vm.bind_async_flags =

drivers/gpu/drm/i915/gt/intel_gtt.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -154,7 +154,22 @@ void i915_address_space_init(struct i915_address_space *vm, int subclass)
		*/
		mutex_init(&vm->mutex);
		lockdep_set_subclass(&vm->mutex, subclass);

		if (!intel_vm_no_concurrent_access_wa(vm->i915)) {
		i915_gem_shrinker_taints_mutex(vm->i915, &vm->mutex);
		} else {
		/*
		* CHV + BXT VTD workaround use stop_machine(),
		* which is allowed to allocate memory. This means &vm->mutex
		* is the outer lock, and in theory we can allocate memory inside
		* it through stop_machine().
		*
		* Add the annotation for this, we use trylock in shrinker.
		*/
		mutex_acquire(&vm->mutex.dep_map, 0, 0, _THIS_IP_);
		might_alloc(GFP_KERNEL);
		mutex_release(&vm->mutex.dep_map, _THIS_IP_);
		}
		dma_resv_init(&vm->resv);

		GEM_BUG_ON(!vm->total);

drivers/gpu/drm/i915/i915_drv.h

+9 −2

Original line number	Diff line number	Diff line
		@@ -1720,9 +1720,15 @@ static inline bool intel_scanout_needs_vtd_wa(struct drm_i915_private *dev_priv)
		}

		static inline bool
		intel_ggtt_update_needs_vtd_wa(struct drm_i915_private *dev_priv)
		intel_ggtt_update_needs_vtd_wa(struct drm_i915_private *i915)
		{
		return IS_BROXTON(dev_priv) && intel_vtd_active();
		return IS_BROXTON(i915) && intel_vtd_active();
		}

		static inline bool
		intel_vm_no_concurrent_access_wa(struct drm_i915_private *i915)
		{
		return IS_CHERRYVIEW(i915) \|\| intel_ggtt_update_needs_vtd_wa(i915);
		}

		/* i915_drv.c */
		@@ -1802,6 +1808,7 @@ int i915_gem_object_unbind(struct drm_i915_gem_object *obj,
		#define I915_GEM_OBJECT_UNBIND_ACTIVE BIT(0)
		#define I915_GEM_OBJECT_UNBIND_BARRIER BIT(1)
		#define I915_GEM_OBJECT_UNBIND_TEST BIT(2)
		#define I915_GEM_OBJECT_UNBIND_VM_TRYLOCK BIT(3)

		void i915_gem_runtime_suspend(struct drm_i915_private *dev_priv);

drivers/gpu/drm/i915/i915_gem.c

+13 −2

Original line number	Diff line number	Diff line
		@@ -157,8 +157,19 @@ int i915_gem_object_unbind(struct drm_i915_gem_object *obj,
		if (vma) {
		ret = -EBUSY;
		if (flags & I915_GEM_OBJECT_UNBIND_ACTIVE \|\|
		!i915_vma_is_active(vma))
		!i915_vma_is_active(vma)) {
		if (i915_is_ggtt(vma->vm) &&
		flags & I915_GEM_OBJECT_UNBIND_VM_TRYLOCK) {
		if (mutex_trylock(&vma->vm->mutex)) {
		ret = __i915_vma_unbind(vma);
		mutex_unlock(&vma->vm->mutex);
		} else {
		ret = -EBUSY;
		}
		} else {
		ret = i915_vma_unbind(vma);
		}
		}

		__i915_vma_put(vma);
		}