On Wed, Oct 11, 2017 at 03:18:57PM +0100, Chris Wilson wrote:
> Purely to silence lockdep, as we know that no bo can exist at this time
> and so the inversion is impossible. Nevertheless, lockdep currently
> warns on unload:
>
> [ 137.522565] WARNING: possible circular locking dependency detected
> [ 137.522568] 4.14.0-rc4-CI-CI_DRM_3209+ #1 Tainted: G U
> [ 137.522570] ------------------------------------------------------
> [ 137.522572] drv_module_relo/1532 is trying to acquire lock:
> [ 137.522574] ("i915-userptr-acquire"){+.+.}, at: [<ffffffff8109a831>] flush_workqueue+0x91/0x540
> [ 137.522581]
> but task is already holding lock:
> [ 137.522583] (&dev->struct_mutex){+.+.}, at: [<ffffffffa014fb3f>] i915_gem_fini+0x3f/0xc0 [i915]
> [ 137.522605]
> which lock already depends on the new lock.
>
> [ 137.522608]
> the existing dependency chain (in reverse order) is:
> [ 137.522611]
> -> #3 (&dev->struct_mutex){+.+.}:
> [ 137.522615] __lock_acquire+0x1420/0x15e0
> [ 137.522618] lock_acquire+0xb0/0x200
> [ 137.522621] __mutex_lock+0x86/0x9b0
> [ 137.522623] mutex_lock_interruptible_nested+0x1b/0x20
> [ 137.522640] i915_mutex_lock_interruptible+0x51/0x130 [i915]
> [ 137.522657] i915_gem_fault+0x20b/0x720 [i915]
> [ 137.522660] __do_fault+0x1e/0x80
> [ 137.522662] __handle_mm_fault+0xa08/0xed0
> [ 137.522664] handle_mm_fault+0x156/0x300
> [ 137.522666] __do_page_fault+0x2c5/0x570
> [ 137.522668] do_page_fault+0x28/0x250
> [ 137.522671] page_fault+0x22/0x30
> [ 137.522672]
> -> #2 (&mm->mmap_sem){++++}:
> [ 137.522677] __lock_acquire+0x1420/0x15e0
> [ 137.522679] lock_acquire+0xb0/0x200
> [ 137.522682] down_read+0x3e/0x70
> [ 137.522699] __i915_gem_userptr_get_pages_worker+0x141/0x240 [i915]
> [ 137.522701] process_one_work+0x233/0x660
> [ 137.522704] worker_thread+0x4e/0x3b0
> [ 137.522706] kthread+0x152/0x190
> [ 137.522708] ret_from_fork+0x27/0x40
> [ 137.522710]
> -> #1 ((&work->work)){+.+.}:
> [ 137.522714] __lock_acquire+0x1420/0x15e0
> [ 137.522717] lock_acquire+0xb0/0x200
> [ 137.522719] process_one_work+0x206/0x660
> [ 137.522721] worker_thread+0x4e/0x3b0
> [ 137.522723] kthread+0x152/0x190
> [ 137.522725] ret_from_fork+0x27/0x40
> [ 137.522727]
> -> #0 ("i915-userptr-acquire"){+.+.}:
> [ 137.522731] check_prev_add+0x430/0x840
> [ 137.522733] __lock_acquire+0x1420/0x15e0
> [ 137.522735] lock_acquire+0xb0/0x200
> [ 137.522738] flush_workqueue+0xb4/0x540
> [ 137.522740] drain_workqueue+0xd4/0x1b0
> [ 137.522742] destroy_workqueue+0x1c/0x200
> [ 137.522758] i915_gem_cleanup_userptr+0x15/0x20 [i915]
> [ 137.522770] i915_gem_fini+0x5f/0xc0 [i915]
> [ 137.522782] i915_driver_unload+0x122/0x180 [i915]
> [ 137.522794] i915_pci_remove+0x19/0x30 [i915]
> [ 137.522797] pci_device_remove+0x39/0xb0
> [ 137.522800] device_release_driver_internal+0x15d/0x220
> [ 137.522803] driver_detach+0x40/0x80
> [ 137.522805] bus_remove_driver+0x58/0xd0
> [ 137.522807] driver_unregister+0x2c/0x40
> [ 137.522809] pci_unregister_driver+0x36/0xb0
> [ 137.522828] i915_exit+0x1a/0x8b [i915]
> [ 137.522831] SyS_delete_module+0x18c/0x1e0
> [ 137.522834] entry_SYSCALL_64_fastpath+0x1c/0xb1
> [ 137.522835]
> other info that might help us debug this:
>
> [ 137.522838] Chain exists of:
> "i915-userptr-acquire" --> &mm->mmap_sem --> &dev->struct_mutex
>
> [ 137.522844] Possible unsafe locking scenario:
>
> [ 137.522846] CPU0 CPU1
> [ 137.522848] ---- ----
> [ 137.522850] lock(&dev->struct_mutex);
> [ 137.522852] lock(&mm->mmap_sem);
> [ 137.522854] lock(&dev->struct_mutex);
> [ 137.522857] lock("i915-userptr-acquire");
> [ 137.522859]
> *** DEADLOCK ***
>
> [ 137.522862] 3 locks held by drv_module_relo/1532:
> [ 137.522864] #0: (&dev->mutex){....}, at: [<ffffffff8161d47b>] device_release_driver_internal+0x2b/0x220
> [ 137.522869] #1: (&dev->mutex){....}, at: [<ffffffff8161d489>] device_release_driver_internal+0x39/0x220
> [ 137.522873] #2: (&dev->struct_mutex){+.+.}, at: [<ffffffffa014fb3f>] i915_gem_fini+0x3f/0xc0 [i915]
> [ 137.522888]
> stack backtrace:
> [ 137.522891] CPU: 0 PID: 1532 Comm: drv_module_relo Tainted: G U 4.14.0-rc4-CI-CI_DRM_3209+ #1
> [ 137.522894] Hardware name: /NUC7i5BNB, BIOS BNKBL357.86A.0048.2017.0704.1415 07/04/2017
> [ 137.522897] Call Trace:
> [ 137.522900] dump_stack+0x68/0x9f
> [ 137.522902] print_circular_bug+0x235/0x3c0
> [ 137.522905] ? lockdep_init_map_crosslock+0x20/0x20
> [ 137.522908] check_prev_add+0x430/0x840
> [ 137.522919] ? i915_gem_fini+0x5f/0xc0 [i915]
> [ 137.522922] ? __kernel_text_address+0x12/0x40
> [ 137.522925] ? __save_stack_trace+0x66/0xd0
> [ 137.522928] __lock_acquire+0x1420/0x15e0
> [ 137.522930] ? __lock_acquire+0x1420/0x15e0
> [ 137.522933] ? lockdep_init_map_crosslock+0x20/0x20
> [ 137.522936] ? __this_cpu_preempt_check+0x13/0x20
> [ 137.522938] lock_acquire+0xb0/0x200
> [ 137.522940] ? flush_workqueue+0x91/0x540
> [ 137.522943] flush_workqueue+0xb4/0x540
> [ 137.522945] ? flush_workqueue+0x91/0x540
> [ 137.522948] ? __mutex_unlock_slowpath+0x43/0x2c0
> [ 137.522951] ? trace_hardirqs_on_caller+0xe3/0x1b0
> [ 137.522954] drain_workqueue+0xd4/0x1b0
> [ 137.522956] ? drain_workqueue+0xd4/0x1b0
> [ 137.522958] destroy_workqueue+0x1c/0x200
> [ 137.522975] i915_gem_cleanup_userptr+0x15/0x20 [i915]
> [ 137.522987] i915_gem_fini+0x5f/0xc0 [i915]
> [ 137.523000] i915_driver_unload+0x122/0x180 [i915]
> [ 137.523015] i915_pci_remove+0x19/0x30 [i915]
> [ 137.523018] pci_device_remove+0x39/0xb0
> [ 137.523021] device_release_driver_internal+0x15d/0x220
> [ 137.523023] driver_detach+0x40/0x80
> [ 137.523026] bus_remove_driver+0x58/0xd0
> [ 137.523028] driver_unregister+0x2c/0x40
> [ 137.523030] pci_unregister_driver+0x36/0xb0
> [ 137.523049] i915_exit+0x1a/0x8b [i915]
> [ 137.523052] SyS_delete_module+0x18c/0x1e0
> [ 137.523055] entry_SYSCALL_64_fastpath+0x1c/0xb1
> [ 137.523057] RIP: 0033:0x7f7bd0609287
> [ 137.523059] RSP: 002b:00007ffef694bc18 EFLAGS: 00000246 ORIG_RAX: 00000000000000b0
> [ 137.523062] RAX: ffffffffffffffda RBX: ffffffff81493f33 RCX: 00007f7bd0609287
> [ 137.523065] RDX: 0000000000000001 RSI: 0000000000000800 RDI: 0000564f999f9fc8
> [ 137.523067] RBP: ffffc90005c4ff88 R08: 0000000000000000 R09: 0000000000000080
> [ 137.523069] R10: 00007f7bd20ef8c0 R11: 0000000000000246 R12: 0000000000000000
> [ 137.523072] R13: 00007ffef694be00 R14: 0000000000000000 R15: 0000000000000000
> [ 137.523075] ? __this_cpu_preempt_check+0x13/0x20
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_drv.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 9af5c369d19e..3bef650c3d62 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -616,9 +616,10 @@ static void i915_gem_fini(struct drm_i915_private *dev_priv)
> intel_uc_fini_hw(dev_priv);
> i915_gem_cleanup_engines(dev_priv);
> i915_gem_contexts_fini(dev_priv);
> - i915_gem_cleanup_userptr(dev_priv);
I think it'd be good if we could push locks like this down further,
instead of sprawling them like this. Slow steps away from a bkl.
Anyway, this looks good.
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Plus push once CI has gotten around to it too ...
-Daniel
> mutex_unlock(&dev_priv->drm.struct_mutex);
>
> + i915_gem_cleanup_userptr(dev_priv);
> +
> i915_gem_drain_freed_objects(dev_priv);
>
> WARN_ON(!list_empty(&dev_priv->contexts.list));
> --
> 2.15.0.rc0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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