linux-kernel - Re: ipmi_msghandler.c question

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Date:   Fri, 8 Jan 2021 20:28:15 -0600
From:   Corey Minyard <minyard@....org>
To:     Asmaa Mnebhi <asmaa@...dia.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: ipmi_msghandler.c question

On Fri, Jan 08, 2021 at 11:37:04PM +0000, Asmaa Mnebhi wrote:
> Hi Corey,
> 
> I have a question for you related to the following function in ipmi_msghandler.c
> 
> static void __get_guid(struct ipmi_smi *intf)
> {
> 	int 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)
> 		/* Send failed, no GUID available. */
> 		bmc->dyn_guid_set = 0;
> 	else
> 		wait_event(intf->waitq, bmc->dyn_guid_set != 2);
> 
> 	/* dyn_guid_set makes the guid data available. */
> 	smp_rmb();
> 
> 	intf->null_user_handler = NULL;
> }
> 
> Why is wait_event used as opposed to wait_event_timeout? In the context where the dyn_guid_set value doesn't change from 2, this would run forever. Wouldn't we want to timeout after a certain amount of time?
> 

The low-level IPMI driver is guarateed to return a response to a
message, though if something goes wrong with the BMC it can take a few
seconds to return the failure message.  So it shouldn't be an issue.

-corey

> Thanks.
> Asmaa