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

Thu May 23 10:20:57 UTC 2019

On 23/05/2019 11:19, Tvrtko Ursulin wrote:
> 
> 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.

Apart from the locally dereferenced vma being the same ggtt one... :)) 
Okay.. Is it worth a comment?

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Regards,

Tvrtko