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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>
Linux kernel
============
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In order to build the documentation, use ``make htmldocs`` or
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