linux-kernel - Re: [PATCH v4 1/3] venus: core: handle race condititon for core ops

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Date:   Mon, 21 Sep 2020 00:15:03 +0300
From:   Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:     Mansur Alisha Shaik <mansur@...eaurora.org>,
        linux-media@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        vgarodia@...eaurora.org
Subject: Re: [PATCH v4 1/3] venus: core: handle race condititon for core ops



On 9/16/20 11:49 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 CPU
> core, core->ops becoming NULL and in another CPU core
> calling core->ops->session_init().
> 
> CPU: core-7:
> Call trace:
>  hfi_session_init+0x180/0x1dc [venus_core]
>  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@...eaurora.org>
> Acked-by: Stanimir Varbanov <stanimir.varbanov@...aro.org>
> ---
> Changes in V4:
> - Addressed review comments by Stan in patch series 
>   https://lore.kernel.org/patchwork/patch/1303678/
>   and combining this change along with shutdown callback
>   as we are facing race conditions with shutdown callback
> 
>  drivers/media/platform/qcom/venus/hfi.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/qcom/venus/hfi.c b/drivers/media/platform/qcom/venus/hfi.c
> index a59022a..58d4c06 100644
> --- a/drivers/media/platform/qcom/venus/hfi.c
> +++ b/drivers/media/platform/qcom/venus/hfi.c
> @@ -195,19 +195,34 @@ 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 core shutdown is in progress or if we are in system
> +	 * recovery, return an error as during system error recovery
> +	 * session_init() can't pass successfully
> +	 */
> +	mutex_lock(&core->lock);
> +	if (!core->ops || core->sys_error) {
> +		mutex_unlock(&core->lock);
> +		return -EIO;
> +	}
> +	mutex_unlock(&core->lock);
> +
>  	if (inst->state != INST_UNINIT)
>  		return -EINVAL;
>  
>  	inst->hfi_codec = to_codec_type(pixfmt);
>  	reinit_completion(&inst->done);
>  
> +	mutex_lock(&core->lock);
> +	ops = core->ops;

This is not needed because we check core->ops for NULL under mutex held
at the beginning of the function. Just keep ops initialization as it is
in the original code.

>  	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