[Intel-gfx] [PATCH] drm/i915/gtt: Always acquire struct_mutex for gen6_ppgtt_cleanup

Thu May 23 10:19:30 UTC 2019

On 23/05/2019 11:14, Chris Wilson wrote:
> Quoting Chris Wilson (2019-05-23 11:07:50)
>> Quoting Tvrtko Ursulin (2019-05-23 11:01:09)
>>>
>>> On 23/05/2019 10:21, Tvrtko Ursulin wrote:
>>>>
>>>> On 23/05/2019 07:49, Chris Wilson wrote:
>>>>> We rearranged the vm_destroy_ioctl to avoid taking struct_mutex, little
>>>>> realising that buried underneath the gen6 ppgtt release path was a
>>>>> struct_mutex requirement (to remove its GGTT vma). Until that
>>>>> struct_mutex is vanquished, take a detour in gen6_ppgtt_cleanup to do
>>>>> the i915_vma_destroy from inside a worker under the struct_mutex.
>>>>>
>>>>> <4> [257.740160] WARN_ON(debug_locks &&
>>>>> !lock_is_held(&(&vma->vm->i915->drm.struct_mutex)->dep_map))
>>>>> <4> [257.740213] WARNING: CPU: 3 PID: 1507 at
>>>>> drivers/gpu/drm/i915/i915_vma.c:841 i915_vma_destroy+0x1ae/0x3a0 [i915]
>>>>> <4> [257.740214] Modules linked in: snd_hda_codec_hdmi i915
>>>>> x86_pkg_temp_thermal mei_hdcp coretemp crct10dif_pclmul crc32_pclmul
>>>>> ghash_clmulni_intel snd_hda_codec_realtek snd_hda_codec_generic
>>>>> snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core r8169 realtek
>>>>> snd_pcm mei_me mei prime_numbers lpc_ich
>>>>> <4> [257.740224] CPU: 3 PID: 1507 Comm: gem_vm_create Tainted: G
>>>>> U            5.2.0-rc1-CI-CI_DRM_6118+ #1
>>>>> <4> [257.740225] Hardware name: MSI MS-7924/Z97M-G43(MS-7924), BIOS
>>>>> V1.12 02/15/2016
>>>>> <4> [257.740249] RIP: 0010:i915_vma_destroy+0x1ae/0x3a0 [i915]
>>>>> <4> [257.740250] Code: 00 00 00 48 81 c7 c8 00 00 00 e8 ed 08 f0 e0 85
>>>>> c0 0f 85 78 fe ff ff 48 c7 c6 e8 ec 30 a0 48 c7 c7 da 55 33 a0 e8 42
>>>>> 8c e9 e0 <0f> 0b 8b 83 40 01 00 00 85 c0 0f 84 63 fe ff ff 48 c7 c1 c1
>>>>> 58 33
>>>>> <4> [257.740251] RSP: 0018:ffffc90000aafc68 EFLAGS: 00010282
>>>>> <4> [257.740252] RAX: 0000000000000000 RBX: ffff8883f7957840 RCX:
>>>>> 0000000000000003
>>>>> <4> [257.740253] RDX: 0000000000000046 RSI: 0000000000000006 RDI:
>>>>> ffffffff8212d1b9
>>>>> <4> [257.740254] RBP: ffffc90000aafcc8 R08: 0000000000000000 R09:
>>>>> 0000000000000000
>>>>> <4> [257.740255] R10: 0000000000000000 R11: 0000000000000000 R12:
>>>>> ffff8883f4d5c2a8
>>>>> <4> [257.740256] R13: ffff8883f4d5d680 R14: ffff8883f4d5c668 R15:
>>>>> ffff8883f4d5c2f0
>>>>> <4> [257.740257] FS:  00007f777fa8fe40(0000) GS:ffff88840f780000(0000)
>>>>> knlGS:0000000000000000
>>>>> <4> [257.740258] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>> <4> [257.740259] CR2: 00007f777f6522b0 CR3: 00000003c612a006 CR4:
>>>>> 00000000001606e0
>>>>> <4> [257.740260] Call Trace:
>>>>> <4> [257.740283]  gen6_ppgtt_cleanup+0x25/0x60 [i915]
>>>>> <4> [257.740306]  i915_ppgtt_release+0x102/0x290 [i915]
>>>>> <4> [257.740330]  i915_gem_vm_destroy_ioctl+0x7c/0xa0 [i915]
>>>>> <4> [257.740376]  ? i915_gem_vm_create_ioctl+0x160/0x160 [i915]
>>>>> <4> [257.740379]  drm_ioctl_kernel+0x83/0xf0
>>>>> <4> [257.740382]  drm_ioctl+0x2f3/0x3b0
>>>>> <4> [257.740422]  ? i915_gem_vm_create_ioctl+0x160/0x160 [i915]
>>>>> <4> [257.740426]  ? _raw_spin_unlock_irqrestore+0x39/0x60
>>>>> <4> [257.740430]  do_vfs_ioctl+0xa0/0x6e0
>>>>> <4> [257.740433]  ? lock_acquire+0xa6/0x1c0
>>>>> <4> [257.740436]  ? __task_pid_nr_ns+0xb9/0x1f0
>>>>> <4> [257.740439]  ksys_ioctl+0x35/0x60
>>>>> <4> [257.740441]  __x64_sys_ioctl+0x11/0x20
>>>>> <4> [257.740443]  do_syscall_64+0x55/0x1c0
>>>>> <4> [257.740445]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>>>
>>>>> References: e0695db7298e ("drm/i915: Create/destroy VM (ppGTT) for use
>>>>> with contexts")
>>>>> Fixes: 7f3f317a66ca ("drm/i915: Restore control over ppgtt for context
>>>>> creation ABI")
>>>>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>>>>> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>>>> ---
>>>>>    drivers/gpu/drm/i915/i915_gem_gtt.c | 32 +++++++++++++++++++++++++++--
>>>>>    drivers/gpu/drm/i915/i915_gem_gtt.h |  2 ++
>>>>>    2 files changed, 32 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c
>>>>> b/drivers/gpu/drm/i915/i915_gem_gtt.c
>>>>> index 9ed41aefb456..5a350251766a 100644
>>>>> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
>>>>> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
>>>>> @@ -1828,11 +1828,33 @@ static void gen6_ppgtt_free_pd(struct
>>>>> gen6_hw_ppgtt *ppgtt)
>>>>>                free_pt(&ppgtt->base.vm, pt);
>>>>>    }
>>>>> +struct gen6_ppgtt_cleanup_work {
>>>>> +    struct work_struct base;
>>>>> +    struct i915_vma *vma;
>>>>> +};
>>>>> +
>>>>> +static void gen6_ppgtt_cleanup_work(struct work_struct *wrk)
>>>>> +{
>>>>> +    struct gen6_ppgtt_cleanup_work *work =
>>>>> +        container_of(wrk, typeof(*work), base);
>>>>> +    struct drm_i915_private *i915 = work->vma->vm->i915;
>>>>
>>>> Does the sequence need an extra reference on ppgtt for dereferencing the
>>>> vm here? Alternatively storing i915 in the work struct could work around
>>>> that.
>>>
>>> Nope - vma has a pointer to vm as well which it will dereference. So if
>>> reference is needed it's needed - it looks like it is to me, since only
>>> contexts take them, which vma's still rely on, right?
>>
>> Nah, vm is decidedly dead at this point, we just need to stuff the i915
>> pointer into the cleanup_work.
> 
> Argh. vma is in ggtt, so vma->vm is alive and kicking -- not the vm we
> just destroyed.

Why is this an argh? :) Doesn't it mean you were right - just storing a 
pointer to i915 in work struct should work. I missed the fact they are 
two separate VMs.

Regards,

Tvrtko