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Date:   Mon, 7 Sep 2020 19:07:53 -0500
From:   Corey Minyard <minyard@acm.org>
To:     Markus Boehme <markubo@amazon.com>
Cc:     openipmi-developer@lists.sourceforge.net,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, Stefan Nuernberger <snu@amazon.com>,
        SeongJae Park <sjpark@amazon.com>, Amit Shah <aams@amazon.com>
Subject: Re: [PATCH 2/3] ipmi: Add timeout waiting for device GUID
Message-ID: <20200908000753.GC15602@minyard.net>
Reply-To: minyard@acm.org
References: <1599495937-10654-1-git-send-email-markubo@amazon.com>
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On Mon, Sep 07, 2020 at 06:25:36PM +0200, Markus Boehme wrote:
> We have observed hosts with misbehaving BMCs that receive a Get Device
> GUID command but don't respond. This leads to an indefinite wait in the
> ipmi_msghandler's __get_guid function, showing up as hung task messages
> for modprobe.
> 
> According to IPMI 2.0 specification chapter 20, the implementation of
> the Get Device GUID command is optional. Therefore, add a timeout to
> waiting for its response and treat the lack of one the same as missing a
> device GUID.

This patch looks good.  It's a little bit of a rewrite, but the reasons
are obvious.

-corey

> 
> Signed-off-by: Stefan Nuernberger <snu@amazon.com>
> Signed-off-by: Markus Boehme <markubo@amazon.com>
> ---
>  drivers/char/ipmi/ipmi_msghandler.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index 2b213c9..2a2e8b2 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -3184,18 +3184,26 @@ static void guid_handler(struct ipmi_smi *intf, struct ipmi_recv_msg *msg)
>  
>  static void __get_guid(struct ipmi_smi *intf)
>  {
> -	int rv;
> +	long rv;
>  	struct bmc_device *bmc = intf->bmc;
>  
>  	bmc->dyn_guid_set = 2;
>  	intf->null_user_handler = guid_handler;
>  	rv = send_guid_cmd(intf, 0);
> -	if (rv)
> +	if (rv) {
>  		/* Send failed, no GUID available. */
>  		bmc->dyn_guid_set = 0;
> -	else
> -		wait_event(intf->waitq, bmc->dyn_guid_set != 2);
> +		goto out;
> +	}
>  
> +	rv = wait_event_timeout(intf->waitq, bmc->dyn_guid_set != 2, 5 * HZ);
> +	if (rv == 0) {
> +		dev_warn_once(intf->si_dev,
> +			      "Timed out waiting for GUID. Assuming GUID is not available.\n");
> +		bmc->dyn_guid_set = 0;
> +	}
> +
> +out:
>  	/* dyn_guid_set makes the guid data available. */
>  	smp_rmb();
>  
> -- 
> 2.7.4
>