[igt-dev] ✓ Fi.CI.IGT: success for tests/gem_userptr_blits: Enhance invalid mapping exercise

Mon Feb 10 11:20:18 UTC 2020

(adding intel-gfx to the loop)

Hi Chris,

On Wednesday, January 29, 2020 12:24:39 PM CET Chris Wilson wrote:
> Quoting Patchwork (2020-01-23 20:22:25)
> > == Series Details ==
> > 
> > Series: tests/gem_userptr_blits: Enhance invalid mapping exercise
> > URL   : https://patchwork.freedesktop.org/series/72411/
> > State : success
> > 
> > == Summary ==
> > 
> > CI Bug Log - changes from CI_DRM_7794_full -> IGTPW_3969_full
> > ====================================================
> > 
> > Summary
> > -------
> > 
> >   **SUCCESS**
> > 
> >   No regressions found.
> > 
> >   External URL: https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_3969/
index.html
> > 
> > New tests
> > ---------
> > 
> >   New tests have been introduced between CI_DRM_7794_full and 
IGTPW_3969_full:
> > 
> > ### New IGT tests (3) ###
> > 
> >   * igt at gem_userptr_blits@invalid-uc-mapping:
> >     - Statuses : 7 pass(s)
> >     - Exec time: [0.01, 0.02] s
> > 
> >   * igt at gem_userptr_blits@invalid-wb-mapping:
> >     - Statuses : 7 pass(s)
> >     - Exec time: [0.01, 0.02] s
> > 
> >   * igt at gem_userptr_blits@invalid-wc-mapping:
> >     - Statuses : 7 pass(s)
> >     - Exec time: [0.01, 0.02] s
> 
> Ok, we need a bit more work to trigger the lockdep loop. We need a 
> cancel_userptr of the same object that is faulted via mmap-offset.

Does that mean it would be helpful if we could trigger that lockdep loop form 
gem_userptr_blits at invalid-*-mapping so we should focus on that?

My confusion also resulted partially from me not being able to find anything 
like cancel_userptr in the current code.  Anyway, I've been trying to find out 
a solution.  While working on that, I found there was a cancel_userptr() 
function but it had been dropped by commit 484d9a844d0d ("drm/i915/userptr: 
Avoid struct_mutex recursion for mmu_invalidate_range_start").

Other than that, it was not clear for me if what you tried to say was we 
needed that cancel_userptr for triggering the lockdep loop, or we needed it 
for having the issue resolved.

Anyway, taking into account that cancel_userptr() is no longer available, 
could you please give me another hint before I spend more time possibly going 
in a wrong direction?

Thanks,
Janusz

> 
> We're basically looking for the equivalent of this
> 
> <4> [175.968441] ======================================================
> <4> [175.968444] WARNING: possible circular locking dependency detected
> <4> [175.968447] 5.5.0-CI-CI_DRM_7828+ #1 Tainted: G     U
> <4> [175.968449] ------------------------------------------------------
> <4> [175.968452] gem_userptr_bli/1564 is trying to acquire lock:
> <4> [175.968455] ffff888208f49580 (&vm->mutex){+.+.}, at: 
i915_vma_unbind+0xae/0x110 [i915]
> <4> [175.968527]
> but task is already holding lock:
> <4> [175.968529] ffffffff82664d40 (mmu_notifier_invalidate_range_start){+.
+.}, at: unmap_vmas+0x0/0x150
> <4> [175.968535]
> which lock already depends on the new lock.
> <4> [175.968538]
> the existing dependency chain (in reverse order) is:
> <4> [175.968541]
> -> #2 (mmu_notifier_invalidate_range_start){+.+.}:
> <4> [175.968546]        page_mkclean_one+0xda/0x210
> <4> [175.968548]        rmap_walk_file+0xff/0x260
> <4> [175.968551]        page_mkclean+0x9f/0xb0
> <4> [175.968555]        clear_page_dirty_for_io+0xa2/0x2f0
> <4> [175.968559]        mpage_submit_page+0x1a/0x70
> <4> [175.968561]        mpage_process_page_bufs+0xe7/0x110
> <4> [175.968564]        mpage_prepare_extent_to_map+0x1d2/0x2b0
> <4> [175.968568]        ext4_writepages+0x5ba/0x12b0
> <4> [175.968571]        do_writepages+0x46/0xe0
> <4> [175.968573]        __filemap_fdatawrite_range+0xc6/0x100
> <4> [175.968576]        file_write_and_wait_range+0x3c/0x90
> <4> [175.968579]        ext4_sync_file+0x1a4/0x540
> <4> [175.968582]        do_fsync+0x33/0x60
> <4> [175.968584]        __x64_sys_fsync+0xb/0x10
> <4> [175.968587]        do_syscall_64+0x4f/0x220
> <4> [175.968591]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> <4> [175.968594]
> -> #1 (&mapping->i_mmap_rwsem){++++}:
> <4> [175.968599]        down_write+0x33/0x70
> <4> [175.968601]        unmap_mapping_pages+0x48/0x130
> <4> [175.968671]        i915_vma_revoke_mmap.part.37+0x66/0x190 [i915]
> <4> [175.968715]        fence_update+0xfd/0x2d0 [i915]
> <4> [175.968759]        __i915_vma_unbind+0x1eb/0x530 [i915]
> <4> [175.968803]        i915_vma_release+0x101/0x220 [i915]
> <4> [175.968843]        __i915_gem_free_objects+0x113/0x530 [i915]
> <4> [175.968886]        i915_gem_create_ioctl+0x12/0x40 [i915]
> <4> [175.968890]        drm_ioctl_kernel+0xad/0xf0
> <4> [175.968893]        drm_ioctl+0x2e1/0x390
> <4> [175.968896]        do_vfs_ioctl+0x9c/0x730
> <4> [175.968899]        ksys_ioctl+0x35/0x60
> <4> [175.968901]        __x64_sys_ioctl+0x11/0x20
> <4> [175.968904]        do_syscall_64+0x4f/0x220
> <4> [175.968906]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> <4> [175.968909]
> -> #0 (&vm->mutex){+.+.}:
> <4> [175.968914]        __lock_acquire+0x1328/0x15d0
> <4> [175.968916]        lock_acquire+0xa7/0x1c0
> <4> [175.968919]        __mutex_lock+0x9a/0x9c0
> <4> [175.968962]        i915_vma_unbind+0xae/0x110 [i915]
> <4> [175.969004]        i915_gem_object_unbind+0x1dc/0x400 [i915]
> <4> [175.969045]        userptr_mn_invalidate_range_start+0xdd/0x190 [i915]
> <4> [175.969049]        __mmu_notifier_invalidate_range_start+0x148/0x250
> <4> [175.969052]        unmap_vmas+0x13e/0x150
> <4> [175.969055]        unmap_region+0xa3/0x100
> <4> [175.969057]        __do_munmap+0x26d/0x490
> <4> [175.969060]        __vm_munmap+0x66/0xc0
> <4> [175.969063]        __x64_sys_munmap+0x12/0x20
> <4> [175.969066]        do_syscall_64+0x4f/0x220
> <4> [175.969068]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> <4> [175.969071]
> 
> cycle but with obj->mm.lock.
> -Chris
> 