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Subject: Re: [RESEND 1/3] venus: core: handle race condititon for core ops
To:     Mansur Alisha Shaik <mansur@codeaurora.org>,
        linux-media@vger.kernel.org, stanimir.varbanov@linaro.org
Cc:     linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        vgarodia@codeaurora.org
References: <1596781478-12216-1-git-send-email-mansur@codeaurora.org>
 <1596781478-12216-2-git-send-email-mansur@codeaurora.org>
From:   Stanimir Varbanov <stanimir.varbanov@linaro.org>
Message-ID: <de32b19e-c643-54d7-0233-c9fe03d4762a@linaro.org>
Date:   Thu, 10 Sep 2020 13:43:37 +0300
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Hi Mansur,

On 8/7/20 9:24 AM, Mansur Alisha Shaik wrote:
> For core ops we are having only write protect but there
> is no read protect, because of this in multthreading
> and concurrency, one CPU core is reading without wait
> which is causing the NULL pointer dereferece crash.
> 
> one such scenario is as show below, where in one
> core core->ops becoming NULL and in another core
> calling core->ops->session_init().
> 
> CPU: core-7:
> Call trace:
>  hfi_session_init+0x180/0x1dc [venus_core]

I thought more on this issue. I think we have to return error from
hfi_session_init() in the case when the driver is in
system-error-handler. Infact all userspace ioctls must end up with error
while we are in recovery state. What do you think?

>  vdec_queue_setup+0x9c/0x364 [venus_dec]
>  vb2_core_reqbufs+0x1e4/0x368 [videobuf2_common]
>  vb2_reqbufs+0x4c/0x64 [videobuf2_v4l2]
>  v4l2_m2m_reqbufs+0x50/0x84 [v4l2_mem2mem]
>  v4l2_m2m_ioctl_reqbufs+0x2c/0x38 [v4l2_mem2mem]
>  v4l_reqbufs+0x4c/0x5c
> __video_do_ioctl+0x2b0/0x39c
> 
> CPU: core-0:
> Call trace:
>  venus_shutdown+0x98/0xfc [venus_core]
>  venus_sys_error_handler+0x64/0x148 [venus_core]
>  process_one_work+0x210/0x3d0
>  worker_thread+0x248/0x3f4
>  kthread+0x11c/0x12c
> 
> Signed-off-by: Mansur Alisha Shaik <mansur@codeaurora.org>
> ---
>  drivers/media/platform/qcom/venus/core.c | 2 +-
>  drivers/media/platform/qcom/venus/hfi.c  | 5 ++++-
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/platform/qcom/venus/core.c b/drivers/media/platform/qcom/venus/core.c
> index 203c653..fe99c83 100644
> --- a/drivers/media/platform/qcom/venus/core.c
> +++ b/drivers/media/platform/qcom/venus/core.c
> @@ -64,8 +64,8 @@ static void venus_sys_error_handler(struct work_struct *work)
>  	pm_runtime_get_sync(core->dev);
>  
>  	hfi_core_deinit(core, true);
> -	hfi_destroy(core);
>  	mutex_lock(&core->lock);
> +	hfi_destroy(core);
>  	venus_shutdown(core);
>  
>  	pm_runtime_put_sync(core->dev);
> diff --git a/drivers/media/platform/qcom/venus/hfi.c b/drivers/media/platform/qcom/venus/hfi.c
> index a211eb9..2eeb31f 100644
> --- a/drivers/media/platform/qcom/venus/hfi.c
> +++ b/drivers/media/platform/qcom/venus/hfi.c
> @@ -195,7 +195,7 @@ EXPORT_SYMBOL_GPL(hfi_session_create);
>  int hfi_session_init(struct venus_inst *inst, u32 pixfmt)
>  {
>  	struct venus_core *core = inst->core;
> -	const struct hfi_ops *ops = core->ops;
> +	const struct hfi_ops *ops;
>  	int ret;
>  
>  	if (inst->state != INST_UNINIT)
> @@ -204,10 +204,13 @@ int hfi_session_init(struct venus_inst *inst, u32 pixfmt)
>  	inst->hfi_codec = to_codec_type(pixfmt);
>  	reinit_completion(&inst->done);
>  
> +	mutex_lock(&core->lock);
> +	ops = core->ops;
>  	ret = ops->session_init(inst, inst->session_type, inst->hfi_codec);
>  	if (ret)
>  		return ret;
>  
> +	mutex_unlock(&core->lock);
>  	ret = wait_session_msg(inst);
>  	if (ret)
>  		return ret;
> 

-- 
regards,
Stan