linux-kernel - Re: [PATCH v5 4/9] PCI: endpoint: Warn and return if EPC is started/stopped multiple times

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Date:   Fri, 2 Jun 2023 08:57:10 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Damien Le Moal <dlemoal@...nel.org>
Cc:     lpieralisi@...nel.org, kw@...ux.com, kishon@...nel.org,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v5 4/9] PCI: endpoint: Warn and return if EPC is
 started/stopped multiple times

On Fri, Jun 02, 2023 at 08:18:58AM +0900, Damien Le Moal wrote:
> On 6/1/23 23:57, Manivannan Sadhasivam wrote:
> > When the EPC is started or stopped multiple times from configfs, just emit
> > a once time warning and return. There is no need to call the EPC start/stop
> > functions in those cases.
> > 
> > Reviewed-by: Kishon Vijay Abraham I <kishon@...nel.org>
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> >  drivers/pci/endpoint/pci-ep-cfs.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/pci/endpoint/pci-ep-cfs.c b/drivers/pci/endpoint/pci-ep-cfs.c
> > index 4b8ac0ac84d5..62c8e09c59f4 100644
> > --- a/drivers/pci/endpoint/pci-ep-cfs.c
> > +++ b/drivers/pci/endpoint/pci-ep-cfs.c
> > @@ -178,6 +178,9 @@ static ssize_t pci_epc_start_store(struct config_item *item, const char *page,
> >  	if (kstrtobool(page, &start) < 0)
> >  		return -EINVAL;
> >  
> > +	if (WARN_ON_ONCE(start == epc_group->start))
> > +		return 0;
> 
> WARN will dump a backtrace which is fairly scary for the user. This case is
> simply a bad user manipulation of the device, so why not simply add a pr_err()
> (optional) and return -EALREADY ?
> 

There EPF core uses WARN_ON_ONCE in other similar places, so thought of sticking
to that pattern. But I agree, WARN_ON_ONCE is not strictly required here. Will
add a error log and return the appropriate error no.

Moreover, will push a patch later to change other instances as well.

- Mani

> > +
> >  	if (!start) {
> >  		pci_epc_stop(epc);
> >  		epc_group->start = 0;
> 
> -- 
> Damien Le Moal
> Western Digital Research
> 

-- 
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