Re: [PATCH v2 1/3] venus: core: handle race condititon for core ops

[Stanimir Varbanov]

On 9/10/20 3:44 PM, 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@xxxxxxxxxxxxxx>
> Acked-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx>
> ---
> Changes in V2:
> - Addressed review comments by stan by validating on top
> - of https://lore.kernel.org/patchwork/project/lkml/list/?series=455962
> 
>  drivers/media/platform/qcom/venus/hfi.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/qcom/venus/hfi.c b/drivers/media/platform/qcom/venus/hfi.c
> index a59022a..3137071 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 we are in system error recovery the session_init cannot pass
successfully, so we exit early in the function.

I'd suggest to make it:

	/* If core shutdown is in progress or we are in system error 	recovery,
return an error */
	mutex_lock(&core->lock);
	if (!core->ops || core->sys_error) {
		mutex_unclock(&core->lock);
		return -EIO;
	}
	mutex_unclock(&core->lock);
		
>  	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