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SubjectRe: [PATCH] drm/i915: Preallocate mmu notifier to unbreak cpu hotplug deadlock
Date
Quoting Daniel Vetter (2017-10-05 14:22:06)
> 4.14-rc1 gained the fancy new cross-release support in lockdep, which
> seems to have uncovered a few more rules about what is allowed and
> isn't.
>
> This one here seems to indicate that allocating a work-queue while
> holding mmap_sem is a no-go, so let's try to preallocate it.
>
> Of course another way to break this chain would be somewhere in the
> cpu hotplug code, since this isn't the only trace we're finding now
> which goes through msr_create_device.
>
> Full lockdep splat:
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.14.0-rc3-CI-CI_DRM_3179+ #1 Tainted: G U
> ------------------------------------------------------
> kworker/3:4/562 is trying to acquire lock:
> (cpu_hotplug_lock.rw_sem){++++}, at: [<ffffffff8113d4bc>] stop_machine+0x1c/0x40
>
> but task is already holding lock:
> (&dev->struct_mutex){+.+.}, at: [<ffffffffa0136588>] i915_reset_device+0x1e8/0x260 [i915]
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #6 (&dev->struct_mutex){+.+.}:
> __lock_acquire+0x1420/0x15e0
> lock_acquire+0xb0/0x200
> __mutex_lock+0x86/0x9b0
> mutex_lock_interruptible_nested+0x1b/0x20
> i915_mutex_lock_interruptible+0x51/0x130 [i915]
> i915_gem_fault+0x209/0x650 [i915]
> __do_fault+0x1e/0x80
> __handle_mm_fault+0xa08/0xed0
> handle_mm_fault+0x156/0x300
> __do_page_fault+0x2c5/0x570
> do_page_fault+0x28/0x250
> page_fault+0x22/0x30
>
> -> #5 (&mm->mmap_sem){++++}:
> __lock_acquire+0x1420/0x15e0
> lock_acquire+0xb0/0x200
> __might_fault+0x68/0x90
> _copy_to_user+0x23/0x70
> filldir+0xa5/0x120
> dcache_readdir+0xf9/0x170
> iterate_dir+0x69/0x1a0
> SyS_getdents+0xa5/0x140
> entry_SYSCALL_64_fastpath+0x1c/0xb1
>
> -> #4 (&sb->s_type->i_mutex_key#5){++++}:
> down_write+0x3b/0x70
> handle_create+0xcb/0x1e0
> devtmpfsd+0x139/0x180
> kthread+0x152/0x190
> ret_from_fork+0x27/0x40
>
> -> #3 ((complete)&req.done){+.+.}:
> __lock_acquire+0x1420/0x15e0
> lock_acquire+0xb0/0x200
> wait_for_common+0x58/0x210
> wait_for_completion+0x1d/0x20
> devtmpfs_create_node+0x13d/0x160
> device_add+0x5eb/0x620
> device_create_groups_vargs+0xe0/0xf0
> device_create+0x3a/0x40
> msr_device_create+0x2b/0x40
> cpuhp_invoke_callback+0xc9/0xbf0
> cpuhp_thread_fun+0x17b/0x240
> smpboot_thread_fn+0x18a/0x280
> kthread+0x152/0x190
> ret_from_fork+0x27/0x40
>
> -> #2 (cpuhp_state-up){+.+.}:
> __lock_acquire+0x1420/0x15e0
> lock_acquire+0xb0/0x200
> cpuhp_issue_call+0x133/0x1c0
> __cpuhp_setup_state_cpuslocked+0x139/0x2a0
> __cpuhp_setup_state+0x46/0x60
> page_writeback_init+0x43/0x67
> pagecache_init+0x3d/0x42
> start_kernel+0x3a8/0x3fc
> x86_64_start_reservations+0x2a/0x2c
> x86_64_start_kernel+0x6d/0x70
> verify_cpu+0x0/0xfb
>
> -> #1 (cpuhp_state_mutex){+.+.}:
> __lock_acquire+0x1420/0x15e0
> lock_acquire+0xb0/0x200
> __mutex_lock+0x86/0x9b0
> mutex_lock_nested+0x1b/0x20
> __cpuhp_setup_state_cpuslocked+0x53/0x2a0
> __cpuhp_setup_state+0x46/0x60
> page_alloc_init+0x28/0x30
> start_kernel+0x145/0x3fc
> x86_64_start_reservations+0x2a/0x2c
> x86_64_start_kernel+0x6d/0x70
> verify_cpu+0x0/0xfb
>
> -> #0 (cpu_hotplug_lock.rw_sem){++++}:
> check_prev_add+0x430/0x840
> __lock_acquire+0x1420/0x15e0
> lock_acquire+0xb0/0x200
> cpus_read_lock+0x3d/0xb0
> stop_machine+0x1c/0x40
> i915_gem_set_wedged+0x1a/0x20 [i915]
> i915_reset+0xb9/0x230 [i915]
> i915_reset_device+0x1f6/0x260 [i915]
> i915_handle_error+0x2d8/0x430 [i915]
> hangcheck_declare_hang+0xd3/0xf0 [i915]
> i915_hangcheck_elapsed+0x262/0x2d0 [i915]
> process_one_work+0x233/0x660
> worker_thread+0x4e/0x3b0
> kthread+0x152/0x190
> ret_from_fork+0x27/0x40
>
> other info that might help us debug this:
>
> Chain exists of:
> cpu_hotplug_lock.rw_sem --> &mm->mmap_sem --> &dev->struct_mutex
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&dev->struct_mutex);
> lock(&mm->mmap_sem);
> lock(&dev->struct_mutex);
> lock(cpu_hotplug_lock.rw_sem);
>
> *** DEADLOCK ***
>
> 3 locks held by kworker/3:4/562:
> #0: ("events_long"){+.+.}, at: [<ffffffff8109c64a>] process_one_work+0x1aa/0x660
> #1: ((&(&i915->gpu_error.hangcheck_work)->work)){+.+.}, at: [<ffffffff8109c64a>] process_one_work+0x1aa/0x660
> #2: (&dev->struct_mutex){+.+.}, at: [<ffffffffa0136588>] i915_reset_device+0x1e8/0x260 [i915]
>
> stack backtrace:
> CPU: 3 PID: 562 Comm: kworker/3:4 Tainted: G U 4.14.0-rc3-CI-CI_DRM_3179+ #1
> Hardware name: /NUC7i5BNB, BIOS BNKBL357.86A.0048.2017.0704.1415 07/04/2017
> Workqueue: events_long i915_hangcheck_elapsed [i915]
> Call Trace:
> dump_stack+0x68/0x9f
> print_circular_bug+0x235/0x3c0
> ? lockdep_init_map_crosslock+0x20/0x20
> check_prev_add+0x430/0x840
> ? irq_work_queue+0x86/0xe0
> ? wake_up_klogd+0x53/0x70
> __lock_acquire+0x1420/0x15e0
> ? __lock_acquire+0x1420/0x15e0
> ? lockdep_init_map_crosslock+0x20/0x20
> lock_acquire+0xb0/0x200
> ? stop_machine+0x1c/0x40
> ? i915_gem_object_truncate+0x50/0x50 [i915]
> cpus_read_lock+0x3d/0xb0
> ? stop_machine+0x1c/0x40
> stop_machine+0x1c/0x40
> i915_gem_set_wedged+0x1a/0x20 [i915]
> i915_reset+0xb9/0x230 [i915]
> i915_reset_device+0x1f6/0x260 [i915]
> ? gen8_gt_irq_ack+0x170/0x170 [i915]
> ? work_on_cpu_safe+0x60/0x60
> i915_handle_error+0x2d8/0x430 [i915]
> ? vsnprintf+0xd1/0x4b0
> ? scnprintf+0x3a/0x70
> hangcheck_declare_hang+0xd3/0xf0 [i915]
> ? intel_runtime_pm_put+0x56/0xa0 [i915]
> i915_hangcheck_elapsed+0x262/0x2d0 [i915]
> process_one_work+0x233/0x660
> worker_thread+0x4e/0x3b0
> kthread+0x152/0x190
> ? process_one_work+0x660/0x660
> ? kthread_create_on_node+0x40/0x40
> ret_from_fork+0x27/0x40
> Setting dangerous option reset - tainting kernel
> i915 0000:00:02.0: Resetting chip after gpu hang
> Setting dangerous option reset - tainting kernel
> i915 0000:00:02.0: Resetting chip after gpu hang

Fwiw, this does not occur on machines with
# CONFI_X86_MSR is not set
-Chris

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