答复: [PATCH] drm/amdgpu:fix race condition bug

[Liu, Monk]

IOCTL will pass a seq value, or 0
And 0 means it want to let KMD choose the latest seq value

So this patch is needed for the caller which input 0 as seq value

I found some code invoke ctx_get_fence() like:

Seq = parm.in.seq ? seq: ctx->rings[ring->idx].sequence -1 ;
Fence = amdgpu_ctx_get_fence(ctx, seq);

BTW: above code is from hybrid kernel branch, not in upstream branch

You can see above logic actually wrong, because the consistence of the sequence is not guaranteed.
Caller should not access sequence directly, 
And sequence should be accessed during protection of the ring_lock


Any idea ?


-----邮件原件-----
发件人: Christian König [mailto:deathsimple at vodafone.de] 
发送时间: 2017年4月7日 19:28
收件人: Liu, Monk <Monk.Liu at amd.com>; amd-gfx at lists.freedesktop.org
主题: Re: [PATCH] drm/amdgpu:fix race condition bug

Am 07.04.2017 um 13:26 schrieb Christian König:
> Am 07.04.2017 um 12:52 schrieb Monk Liu:
>> Change-Id: Ib7a03f3cf5594deeb4ad333cc59b47a6bddfd1ad
>> Signed-off-by: Monk Liu <Monk.Liu at amd.com>
>
> NAK, that is a not backward compatible change to the IOCTL interface.

To make it clear, something like "if(seq == ~0L)" should work.

Christian.

>
> And BTW what's the background of it?
>
> Christian.
>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
>> index 6d86eae..b8c11fe 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
>> @@ -277,6 +277,9 @@ struct fence *amdgpu_ctx_get_fence(struct 
>> amdgpu_ctx *ctx,
>>         spin_lock(&ctx->ring_lock);
>>   +    if (!seq)
>> +        seq = ctx->rings[ring->idx].sequence - 1;
>> +
>>       if (seq >= cring->sequence) {
>>           spin_unlock(&ctx->ring_lock);
>>           return ERR_PTR(-EINVAL);
>
>
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