linux-kernel - Re: [PATCHv3 1/3] media: venus: fix enc/dec destruction order

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Message-ID: <20241025094749.GP1279924@google.com>
Date: Fri, 25 Oct 2024 18:47:49 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Dikshita Agarwal <quic_dikshita@...cinc.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
	Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
	Vikash Garodia <quic_vgarodia@...cinc.com>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tomasz Figa <tfiga@...gle.com>
Subject: Re: [PATCHv3 1/3] media: venus: fix enc/dec destruction order

On (24/10/25 12:50), Dikshita Agarwal wrote:
> > diff --git a/drivers/media/platform/qcom/venus/vdec.c b/drivers/media/platform/qcom/venus/vdec.c
> > index 6252a6b3d4ba..0013c4704f03 100644
> > --- a/drivers/media/platform/qcom/venus/vdec.c
> > +++ b/drivers/media/platform/qcom/venus/vdec.c
> > @@ -1752,13 +1752,14 @@ static int vdec_close(struct file *file)
> >  	cancel_work_sync(&inst->delayed_process_work);
> >  	v4l2_m2m_ctx_release(inst->m2m_ctx);
> >  	v4l2_m2m_release(inst->m2m_dev);
> > -	vdec_ctrl_deinit(inst);
> >  	ida_destroy(&inst->dpb_ids);
> >  	hfi_session_destroy(inst);
> > -	mutex_destroy(&inst->lock);
> > -	mutex_destroy(&inst->ctx_q_lock);
> >  	v4l2_fh_del(&inst->fh);
> >  	v4l2_fh_exit(&inst->fh);
> > +	vdec_ctrl_deinit(inst);
> Why vdec_ctrl_deinit ->v4l2_ctrl_handler_free(&inst->ctrl_handler) needs to
> be called after v4l2_fh_exit?
> Ideally it should be before v4l2_fh_exit.

Because ->fh holds a pointer to ->ctrl_handler

	inst->fh.ctrl_handler = &inst->ctrl_handler

so after vdec_ctrl_deinit() fh holds stale (released) data.
In general destruction in reverse order of initialization is
safer.

init:
	init ctrl
	init fh     // using ctrl

de-init:
	release fh
	release ctrl