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Message-ID: <c6c9b6af-f832-3cc3-2d03-29d5f7aaddef@amd.com>
Date: Mon, 6 Feb 2023 17:05:48 +0100
From: Christian König <christian.koenig@....com>
To: Rob Clark <robdclark@...il.com>
Cc: dri-devel@...ts.freedesktop.org,
Alex Deucher <alexander.deucher@....com>,
Rob Clark <robdclark@...omium.org>,
"Pan, Xinhui" <Xinhui.Pan@....com>,
David Airlie <airlied@...il.com>,
Daniel Vetter <daniel@...ll.ch>,
Felix Kuehling <Felix.Kuehling@....com>,
Philip Yang <Philip.Yang@....com>, Qiang Yu <qiang.yu@....com>,
Jammy Zhou <Jammy.Zhou@....com>,
"open list:RADEON and AMDGPU DRM DRIVERS"
<amd-gfx@...ts.freedesktop.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/amdgpu: Fix potential race processing vm->freed
Am 06.02.23 um 16:52 schrieb Rob Clark:
> On Mon, Feb 6, 2023 at 2:15 AM Christian König <christian.koenig@....com> wrote:
>> Am 03.02.23 um 19:10 schrieb Rob Clark:
>>> From: Rob Clark <robdclark@...omium.org>
>>>
>>> If userspace calls the AMDGPU_CS ioctl from multiple threads, because
>>> the vm is global to the drm_file, you can end up with multiple threads
>>> racing in amdgpu_vm_clear_freed(). So the freed list should be
>>> protected with the status_lock, similar to other vm lists.
>> Well this is nonsense. To process the freed list the VM root PD lock
>> must be held anyway.
>>
>> If we have a call path where this isn't true then we have a major bug at
>> a different place here.
> I'm not super familiar w/ the amdgpu cs parser stuff, but the only
> thing that I'm seeing that protects things is the bo_list_mutex and it
> isn't clear to me that this is 1:1 with the vm (it looks like it is
> not).
Do you have a backtrace?
Take a look at the reservation object of vm->root.bo. This should always
be locked first before doing *anything* in a CS.
If that isn't the case we have a much worse problem.
> (I cc'd you on the bug report, jfyi)
I unfortunately only get a permission denied when I try to access that one.
Regards,
Christian.
>
> BR,
> -R
>
>> Regards,
>> Christian.
>>
>>> Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
>>> Signed-off-by: Rob Clark <robdclark@...omium.org>
>>> ---
>>> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 33 ++++++++++++++++++++++----
>>> 1 file changed, 29 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> index b9441ab457ea..aeed7bc1512f 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> @@ -1240,10 +1240,19 @@ int amdgpu_vm_clear_freed(struct amdgpu_device *adev,
>>> struct amdgpu_bo_va_mapping *mapping;
>>> uint64_t init_pte_value = 0;
>>> struct dma_fence *f = NULL;
>>> + struct list_head freed;
>>> int r;
>>>
>>> - while (!list_empty(&vm->freed)) {
>>> - mapping = list_first_entry(&vm->freed,
>>> + /*
>>> + * Move the contents of the VM's freed list to a local list
>>> + * that we can iterate without racing against other threads:
>>> + */
>>> + spin_lock(&vm->status_lock);
>>> + list_replace_init(&vm->freed, &freed);
>>> + spin_unlock(&vm->status_lock);
>>> +
>>> + while (!list_empty(&freed)) {
>>> + mapping = list_first_entry(&freed,
>>> struct amdgpu_bo_va_mapping, list);
>>> list_del(&mapping->list);
>>>
>>> @@ -1258,6 +1267,15 @@ int amdgpu_vm_clear_freed(struct amdgpu_device *adev,
>>> amdgpu_vm_free_mapping(adev, vm, mapping, f);
>>> if (r) {
>>> dma_fence_put(f);
>>> +
>>> + /*
>>> + * Move any unprocessed mappings back to the freed
>>> + * list:
>>> + */
>>> + spin_lock(&vm->status_lock);
>>> + list_splice_tail(&freed, &vm->freed);
>>> + spin_unlock(&vm->status_lock);
>>> +
>>> return r;
>>> }
>>> }
>>> @@ -1583,11 +1601,14 @@ int amdgpu_vm_bo_unmap(struct amdgpu_device *adev,
>>> mapping->bo_va = NULL;
>>> trace_amdgpu_vm_bo_unmap(bo_va, mapping);
>>>
>>> - if (valid)
>>> + if (valid) {
>>> + spin_lock(&vm->status_lock);
>>> list_add(&mapping->list, &vm->freed);
>>> - else
>>> + spin_unlock(&vm->status_lock);
>>> + } else {
>>> amdgpu_vm_free_mapping(adev, vm, mapping,
>>> bo_va->last_pt_update);
>>> + }
>>>
>>> return 0;
>>> }
>>> @@ -1671,7 +1692,9 @@ int amdgpu_vm_bo_clear_mappings(struct amdgpu_device *adev,
>>> tmp->last = eaddr;
>>>
>>> tmp->bo_va = NULL;
>>> + spin_lock(&vm->status_lock);
>>> list_add(&tmp->list, &vm->freed);
>>> + spin_unlock(&vm->status_lock);
>>> trace_amdgpu_vm_bo_unmap(NULL, tmp);
>>> }
>>>
>>> @@ -1788,7 +1811,9 @@ void amdgpu_vm_bo_del(struct amdgpu_device *adev,
>>> amdgpu_vm_it_remove(mapping, &vm->va);
>>> mapping->bo_va = NULL;
>>> trace_amdgpu_vm_bo_unmap(bo_va, mapping);
>>> + spin_lock(&vm->status_lock);
>>> list_add(&mapping->list, &vm->freed);
>>> + spin_unlock(&vm->status_lock);
>>> }
>>> list_for_each_entry_safe(mapping, next, &bo_va->invalids, list) {
>>> list_del(&mapping->list);
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