On Thu, Feb 13, 2020 at 01:46:41PM +0100, Janusz Krzysztofik wrote:
> map-fixed-invalidate* subtests utilize gem_set_tiling() which may fail,
> e.g. on hardware with no mappable aperture, due to missing fences.
> Skip those subtests if fences are not available.
>
> Moreover, those subtests use GEM_MMAP_GTT IOCTL which may also fail,
> e.g. on hardware with no mappable aperture. Use GEM_MMAP_OFFSET
> instead and iterate MMAP_OFFSET coherent types to find one that works.
>
> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>
> Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> ---
> Hi Michał,
>
> As you are the author of those subtests, let me ask you a few questions
> I'm not sure about:
> 1. How critical is the use of gem_set_tiling() to those subtests? Can
> we just skip those operations if not supported? If not, can you
> propose a replacement that should work on hardware with no mappable
> aperture?
It's a regression test, see:
e4b946bfe1e3 ("drm/i915: Fix userptr deadlock with aliased GTT mmappings")
The idea was to cause a deadlock by triggerring i915_gem_object_release_mmap
from set_tiling underneath struct_mutex, which would then cause invalidate on a
stale userptr (which would also attempt to acquire struct mutex - classic
recursive lock). Original trace which served as an example to write the IGT:
[23106.066196] [drm:i915_gem_open]
[23279.022598] INFO: task test_api64:1359 blocked for more than 120 seconds.
[23279.032453] Tainted: G U 4.1.0-rc7+ #16
[23279.039440] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[23279.049191] test_api64 D ffff880146837a18 12760 1359 530 0x00000000
[23279.058101] ffff880146837a18 ffff8801468379d8 ffffffff8101efcd ffff880147e22e20
[23279.067372] ffff8800a34b8000 ffff8801468379f8 ffff880146838000 00000000ffffffff
[23279.076599] ffff8801459911b0 0000000000000246 ffff8801459911a8 ffff880146837a38
[23279.085923] Call Trace:
[23279.089510] [<ffffffff8101efcd>] ? native_sched_clock+0x2d/0x90
[23279.097223] [<ffffffff817a34a7>] schedule+0x37/0x90
[23279.103662] [<ffffffff817a389e>] schedule_preempt_disabled+0xe/0x10
[23279.111665] [<ffffffff817a5a05>] mutex_lock_nested+0x165/0x3d0
[23279.119287] [<ffffffffa01f7fac>] ? cancel_userptr+0x2c/0x150 [i915]
[23279.127376] [<ffffffff817abf88>] ? ftrace_graph_caller+0x78/0xa8
[23279.135204] [<ffffffffa01f7fac>] ? cancel_userptr+0x2c/0x150 [i915]
[23279.143329] [<ffffffffa01f7fac>] cancel_userptr+0x2c/0x150 [i915]
[23279.151263] [<ffffffff817abfb8>] ftrace_graph_caller+0xa8/0xa8
[23279.158801] [<ffffffffa01f8211>] i915_gem_userptr_mn_invalidate_range_start+0x141/0x200 [i915]
[23279.169559] [<ffffffffa01f80d5>] ? i915_gem_userptr_mn_invalidate_range_start+0x5/0x200 [i915]
[23279.180364] [<ffffffff817abfb8>] ftrace_graph_caller+0xa8/0xa8
[23279.187919] [<ffffffff8120fbb3>] __mmu_notifier_invalidate_range_start+0x83/0xd0
[23279.197342] [<ffffffff8120fb35>] ? __mmu_notifier_invalidate_range_start+0x5/0xd0
[23279.206804] [<ffffffff811e9036>] zap_page_range_single+0xf6/0x120
[23279.214727] [<ffffffff811e9114>] ? unmap_mapping_range+0x64/0x140
[23279.222515] [<ffffffff811e9114>] ? unmap_mapping_range+0x64/0x140
[23279.230489] [<ffffffff811e9114>] ? unmap_mapping_range+0x64/0x140
[23279.238442] [<ffffffff811e91ca>] unmap_mapping_range+0x11a/0x140
[23279.246141] [<ffffffffa01ecba5>] ? i915_gem_release_mmap+0x5/0x20 [i915]
[23279.254753] [<ffffffffa01eb866>] i915_gem_release_mmap.part.44+0x46/0x60 [i915]
[23279.264002] [<ffffffffa01ecbb9>] ? i915_gem_release_mmap+0x19/0x20 [i915]
[23279.272723] [<ffffffff817abfb8>] ftrace_graph_caller+0xa8/0xa8
[23279.280239] [<ffffffffa01ecbb9>] i915_gem_release_mmap+0x19/0x20 [i915]
[23279.288780] [<ffffffff817abfb8>] ftrace_graph_caller+0xa8/0xa8
[23279.296323] [<ffffffffa01f6df4>] i915_gem_set_tiling+0x204/0x540 [i915]
[23279.304854] [<ffffffff817abfb8>] ftrace_graph_caller+0xa8/0xa8
[23279.312559] [<ffffffffa0119a8f>] drm_ioctl+0x12f/0x620 [drm]
[23279.319986] [<ffffffffa01f6bf0>] ? i915_gem_detect_bit_6_swizzle+0x200/0x200 [i915]
[23279.329744] [<ffffffff811eac5e>] ? handle_mm_fault+0xe1e/0x1780
[23279.337380] [<ffffffff8101efcd>] ? native_sched_clock+0x2d/0x90
[23279.345081] [<ffffffff8101f039>] ? sched_clock+0x9/0x10
[23279.352029] [<ffffffff810d3fd5>] ? local_clock+0x25/0x30
[23279.359059] [<ffffffff810ef31f>] ? lock_release_holdtime.part.25+0xf/0x1f0
[23279.367914] [<ffffffff8124fc96>] do_vfs_ioctl+0x2c6/0x4f0
[23279.375068] [<ffffffff810edf13>] ? up_read+0x23/0x40
[23279.381794] [<ffffffff81068cfc>] ? __do_page_fault+0x1bc/0x450
[23279.389356] [<ffffffff8124ff41>] SyS_ioctl+0x81/0xa0
[23279.396025] [<ffffffff817a992e>] system_call_fastpath+0x12/0x76
[23279.403823] 4 locks held by test_api64/1359:
[23279.409505] #0: (&dev->struct_mutex){......}, at: [<ffffffffa01f6ce6>] i915_gem_set_tiling+0xf6/0x540 [i915]
[23279.421939] #1: (&mapping->i_mmap_rwsem){......}, at: [<ffffffff811e9114>] unmap_mapping_range+0x64/0x140
[23279.434071] #2: (&srcu){......}, at: [<ffffffff8120fb35>] __mmu_notifier_invalidate_range_start+0x5/0xd0
[23279.446103] #3: (&dev->struct_mutex){......}, at: [<ffffffffa01f7fac>] cancel_userptr+0x2c/0x150 [i915]
Since then, i915 has changed a lot... (no more struct mutex), so it's hard to
immediately say whether there's still any deadlock potential there.
-Michał
> 2. Which of MMAP_OFFSET types should do the job if mappable aperture is
> not available? Should any of them work, as I've assumed? Is my
> approach of succeeding a subtest on first successful MMAP_OFFSET
> type correct? Or should we examine all types?
>
> Thanks,
> Janusz
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