linux-kernel - Re: [PATCH] firmware loader: don't cancel _nowait requests when helper is not yet available

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Date:	Sun, 18 Mar 2012 23:32:08 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Christian Lamparter <chunkeey@...glemail.com>,
	linux-kernel@...r.kernel.org,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	alan@...rguk.ukuu.org.uk,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] firmware loader: don't cancel _nowait requests when helper
 is not yet available

On 3/18/2012 5:01 AM, Rafael J. Wysocki wrote:
> On Sunday, March 18, 2012, Stephen Boyd wrote:
>
>> Ok. I like where nowait() is going in the other part of the thread but
>> I'm still confused about when request_firmware() is correct to use. It
>> seems that the function is inherently racy with freezing. Does every
>> user of request_firmware() need to synchronize with freezing?
>>
>> For example, if one CPU is in the middle of a driver probe that makes a
>> request_firmware() call and another CPU is starting to suspend we will
>> have a race between usermodehelpers being disabled and the
>> request_firmware() call acquiring the usermodehelper rwsem. If the
>> suspending CPU wins the race it will disable usermodehelpers and the
>> request_firmware() call will return -EBUSY and warn.
> Yes, it will.

That sounds wrong then, no? Why don't we have request_firmware() do a
read_lock on the usermodehelpers sem and then have suspend do a write
lock, disable usermodehelpers, wait for any users  to finish, freeze
processes and then unlock the write lock? That way we don't hit a case
where request_firmware() races with suspend, and we don't have to change
the warning or conditional.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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