[Intel-gfx] [PATCH] drm/i915/userptr: Disallow wrapping GTT into a userptr

[Tvrtko Ursulin]

On 07/03/2017 09:13, Chris Wilson wrote:
> On Tue, Mar 07, 2017 at 08:42:26AM +0000, Tvrtko Ursulin wrote:
>>
>> On 06/03/2017 15:36, Chris Wilson wrote:
>>> If we allow the user to convert a GTT mmap address into a userptr, we
>>> may end up in recursion hell, where currently we hit a mutex deadlock
>>> but other possibilities include use-after-free during the
>>> unbind/cancel_userptr.
>>
>> I thought we already disallowed that and indeed
>> igt/gem_userptr_blits/invalid-gtt-mapping succeeds here - what am I
>> missing?
>
> Michał presented this deadlock:
>
> [  143.203989] gem_userptr_bli D    0   902    898 0x00000000
> [  143.204054] Call Trace:
> [  143.204137]  __schedule+0x511/0x1180
> [  143.204195]  ? pci_mmcfg_check_reserved+0xc0/0xc0
> [  143.204274]  schedule+0x57/0xe0
> [  143.204327]  schedule_timeout+0x383/0x670
> [  143.204374]  ? trace_hardirqs_on_caller+0x187/0x280
> [  143.204457]  ? trace_hardirqs_on_thunk+0x1a/0x1c
> [  143.204507]  ? usleep_range+0x110/0x110
> [  143.204657]  ? irq_exit+0x89/0x100
> [  143.204710]  ? retint_kernel+0x2d/0x2d
> [  143.204794]  ? trace_hardirqs_on_caller+0x187/0x280
> [  143.204857]  ? _raw_spin_unlock_irq+0x33/0x60
> [  143.204944]  wait_for_common+0x1f0/0x2f0
> [  143.205006]  ? out_of_line_wait_on_atomic_t+0x170/0x170
> [  143.205103]  ? wake_up_q+0xa0/0xa0
> [  143.205159]  ? flush_workqueue_prep_pwqs+0x15a/0x2c0
> [  143.205237]  wait_for_completion+0x1d/0x20
> [  143.205292]  flush_workqueue+0x2e9/0xbb0
> [  143.205339]  ? flush_workqueue+0x163/0xbb0
> [  143.205418]  ? __schedule+0x533/0x1180
> [  143.205498]  ? check_flush_dependency+0x1a0/0x1a0
> [  143.205681]  i915_gem_userptr_mn_invalidate_range_start+0x1c7/0x270 [i915]
> [  143.205865]  ? i915_gem_userptr_dmabuf_export+0x40/0x40 [i915]
> [  143.205955]  __mmu_notifier_invalidate_range_start+0xc6/0x120
> [  143.206044]  ? __mmu_notifier_invalidate_range_start+0x51/0x120
> [  143.206123]  zap_page_range_single+0x1c7/0x1f0
> [  143.206171]  ? unmap_single_vma+0x160/0x160
> [  143.206260]  ? unmap_mapping_range+0xa9/0x1b0
> [  143.206308]  ? vma_interval_tree_subtree_search+0x75/0xd0
> [  143.206397]  unmap_mapping_range+0x18f/0x1b0
> [  143.206444]  ? zap_vma_ptes+0x70/0x70
> [  143.206524]  ? __pm_runtime_resume+0x67/0xa0
> [  143.206723]  i915_gem_release_mmap+0x1ba/0x1c0 [i915]
> [  143.206846]  i915_vma_unbind+0x5c2/0x690 [i915]
> [  143.206925]  ? __lock_is_held+0x52/0x100
> [  143.207076]  i915_gem_object_set_tiling+0x1db/0x650 [i915]
> [  143.207236]  i915_gem_set_tiling_ioctl+0x1d3/0x3b0 [i915]
> [  143.207377]  ? i915_gem_set_tiling_ioctl+0x5/0x3b0 [i915]
> [  143.207457]  drm_ioctl+0x36c/0x670
> [  143.207535]  ? debug_lockdep_rcu_enabled.part.0+0x1a/0x30
> [  143.207730]  ? i915_gem_object_set_tiling+0x650/0x650 [i915]
> [  143.207793]  ? drm_getunique+0x120/0x120
> [  143.207875]  ? __handle_mm_fault+0x996/0x14a0
> [  143.207939]  ? vm_insert_page+0x340/0x340
> [  143.208028]  ? up_write+0x28/0x50
> [  143.208086]  ? vm_mmap_pgoff+0x160/0x190
> [  143.208163]  do_vfs_ioctl+0x12c/0xa60
> [  143.208218]  ? debug_lockdep_rcu_enabled+0x35/0x40
> [  143.208267]  ? ioctl_preallocate+0x150/0x150
> [  143.208353]  ? __do_page_fault+0x36a/0x6e0
> [  143.208400]  ? mark_held_locks+0x23/0xc0
> [  143.208479]  ? up_read+0x1f/0x40
> [  143.208526]  ? entry_SYSCALL_64_fastpath+0x5/0xc6
> [  143.208669]  ? __fget_light+0xa7/0xc0
> [  143.208747]  SyS_ioctl+0x41/0x70
> [  143.208808]  entry_SYSCALL_64_fastpath+0x23/0xc6

That would mean another process never exits cancel_userptr, correct? Do 
we have a trace of the other end?

Regards,

Tvrtko