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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. [ 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 To prevent the possibility of a deadlock, we defer scheduling the worker until after we have proven that given the current mm, the userptr range does not overlap a GGTT mmaping. If another thread tries to remap the GGTT over the userptr before the worker is scheduled, it will be stopped by its invalidate-range flushing the current work, before the deadlock can occur. v2: Improve discussion of how we end up in the deadlock. v3: Don't forget to mark the userptr as active after a successful gup_fast. Rename overlaps_ggtt to noncontiguous_or_overlaps_ggtt. v4: Fix test ordering between invalid GTT mmaping and range completion (Tvrtko) Reported-by: Michał Winiarski <michal.winiarski@intel.com> Testcase: igt/gem_userptr_blits/map-fixed-invalidate-gup Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Michał Winiarski <michal.winiarski@intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170308215903.24171-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.