linux-kernel - Re: [PATCH v3 10/16] ipmi: kcs_bmc: Don't enforce single-open policy in the kernel

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Message-ID: <20210521173007.GJ2921206@minyard.net>
Date:   Fri, 21 May 2021 12:30:07 -0500
From:   Corey Minyard <minyard@....org>
To:     Andrew Jeffery <andrew@...id.au>
Cc:     openipmi-developer@...ts.sourceforge.net, openbmc@...ts.ozlabs.org,
        devicetree@...r.kernel.org, tmaimon77@...il.com,
        linux-aspeed@...ts.ozlabs.org, avifishman70@...il.com,
        venture@...gle.com, linux-kernel@...r.kernel.org,
        tali.perry1@...il.com, robh+dt@...nel.org,
        chiawei_wang@...eedtech.com, linux-arm-kernel@...ts.infradead.org,
        benjaminfair@...gle.com, arnd@...db.de, zweiss@...inix.com
Subject: Re: [PATCH v3 10/16] ipmi: kcs_bmc: Don't enforce single-open policy
 in the kernel

On Mon, May 10, 2021 at 03:12:07PM +0930, Andrew Jeffery wrote:
> Soon it will be possible for one KCS device to have multiple associated
> chardevs exposed to userspace (for IPMI and raw-style access). However,
> don't prevent userspace from:
> 
> 1. Opening more than one chardev at a time, or
> 2. Opening the same chardev more than once.
> 
> System behaviour is undefined for both classes of multiple access, so
> userspace must manage itself accordingly.

I don't understand why you want to allow this.  If the second open won't
work right, then why allow it?  Why remove code that causes the second
open to error?

-corey

> 
> The implementation delivers IBF and OBF events to the first chardev
> client to associate with the KCS device. An open on a related chardev
> cannot associate its client with the KCS device and so will not
> receive notification of events. However, any fd on any chardev may race
> their accesses to the data and status registers.
> 
> Signed-off-by: Andrew Jeffery <andrew@...id.au>
> ---
>  drivers/char/ipmi/kcs_bmc.c         | 34 ++++++++++-------------------
>  drivers/char/ipmi/kcs_bmc_aspeed.c  |  3 +--
>  drivers/char/ipmi/kcs_bmc_npcm7xx.c |  3 +--
>  3 files changed, 14 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/char/ipmi/kcs_bmc.c b/drivers/char/ipmi/kcs_bmc.c
> index 7081541bb6ce..ad9ff13ba831 100644
> --- a/drivers/char/ipmi/kcs_bmc.c
> +++ b/drivers/char/ipmi/kcs_bmc.c
> @@ -55,24 +55,12 @@ EXPORT_SYMBOL(kcs_bmc_update_status);
>  irqreturn_t kcs_bmc_handle_event(struct kcs_bmc_device *kcs_bmc)
>  {
>  	struct kcs_bmc_client *client;
> -	irqreturn_t rc;
> +	irqreturn_t rc = IRQ_NONE;
>  
>  	spin_lock(&kcs_bmc->lock);
>  	client = kcs_bmc->client;
> -	if (client) {
> +	if (client)
>  		rc = client->ops->event(client);
> -	} else {
> -		u8 status;
> -
> -		status = kcs_bmc_read_status(kcs_bmc);
> -		if (status & KCS_BMC_STR_IBF) {
> -			/* Ack the event by reading the data */
> -			kcs_bmc_read_data(kcs_bmc);
> -			rc = IRQ_HANDLED;
> -		} else {
> -			rc = IRQ_NONE;
> -		}
> -	}
>  	spin_unlock(&kcs_bmc->lock);
>  
>  	return rc;
> @@ -81,26 +69,28 @@ EXPORT_SYMBOL(kcs_bmc_handle_event);
>  
>  int kcs_bmc_enable_device(struct kcs_bmc_device *kcs_bmc, struct kcs_bmc_client *client)
>  {
> -	int rc;
> -
>  	spin_lock_irq(&kcs_bmc->lock);
> -	if (kcs_bmc->client) {
> -		rc = -EBUSY;
> -	} else {
> +	if (!kcs_bmc->client) {
> +		u8 mask = KCS_BMC_EVENT_TYPE_IBF;
> +
>  		kcs_bmc->client = client;
> -		rc = 0;
> +		kcs_bmc_update_event_mask(kcs_bmc, mask, mask);
>  	}
>  	spin_unlock_irq(&kcs_bmc->lock);
>  
> -	return rc;
> +	return 0;
>  }
>  EXPORT_SYMBOL(kcs_bmc_enable_device);
>  
>  void kcs_bmc_disable_device(struct kcs_bmc_device *kcs_bmc, struct kcs_bmc_client *client)
>  {
>  	spin_lock_irq(&kcs_bmc->lock);
> -	if (client == kcs_bmc->client)
> +	if (client == kcs_bmc->client) {
> +		u8 mask = KCS_BMC_EVENT_TYPE_IBF | KCS_BMC_EVENT_TYPE_OBE;
> +
> +		kcs_bmc_update_event_mask(kcs_bmc, mask, 0);
>  		kcs_bmc->client = NULL;
> +	}
>  	spin_unlock_irq(&kcs_bmc->lock);
>  }
>  EXPORT_SYMBOL(kcs_bmc_disable_device);
> diff --git a/drivers/char/ipmi/kcs_bmc_aspeed.c b/drivers/char/ipmi/kcs_bmc_aspeed.c
> index 8b223e58d900..8a0b1e18e945 100644
> --- a/drivers/char/ipmi/kcs_bmc_aspeed.c
> +++ b/drivers/char/ipmi/kcs_bmc_aspeed.c
> @@ -414,8 +414,7 @@ static int aspeed_kcs_probe(struct platform_device *pdev)
>  
>  	platform_set_drvdata(pdev, priv);
>  
> -	aspeed_kcs_irq_mask_update(kcs_bmc, (KCS_BMC_EVENT_TYPE_IBF | KCS_BMC_EVENT_TYPE_OBE),
> -				   KCS_BMC_EVENT_TYPE_IBF);
> +	aspeed_kcs_irq_mask_update(kcs_bmc, (KCS_BMC_EVENT_TYPE_IBF | KCS_BMC_EVENT_TYPE_OBE), 0);
>  	aspeed_kcs_enable_channel(kcs_bmc, true);
>  
>  	kcs_bmc_add_device(&priv->kcs_bmc);
> diff --git a/drivers/char/ipmi/kcs_bmc_npcm7xx.c b/drivers/char/ipmi/kcs_bmc_npcm7xx.c
> index f8b7162fb830..ab4a8caf1270 100644
> --- a/drivers/char/ipmi/kcs_bmc_npcm7xx.c
> +++ b/drivers/char/ipmi/kcs_bmc_npcm7xx.c
> @@ -202,8 +202,7 @@ static int npcm7xx_kcs_probe(struct platform_device *pdev)
>  	if (rc)
>  		return rc;
>  
> -	npcm7xx_kcs_irq_mask_update(kcs_bmc, (KCS_BMC_EVENT_TYPE_IBF | KCS_BMC_EVENT_TYPE_OBE),
> -				    KCS_BMC_EVENT_TYPE_IBF);
> +	npcm7xx_kcs_irq_mask_update(kcs_bmc, (KCS_BMC_EVENT_TYPE_IBF | KCS_BMC_EVENT_TYPE_OBE), 0);
>  	npcm7xx_kcs_enable_channel(kcs_bmc, true);
>  
>  	pr_info("channel=%u idr=0x%x odr=0x%x str=0x%x\n",
> -- 
> 2.27.0
>