linux-kernel - Re: usermodehelper lock error at resume

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Date:	Tue, 29 Apr 2014 17:34:32 +0200
From:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:	Takashi Iwai <tiwai@...e.de>
CC:	Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Zdenek Herman <zdenek@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: usermodehelper lock error at resume

On 4/29/2014 5:14 PM, Takashi Iwai wrote:
> At Fri, 18 Apr 2014 10:28:05 +0200,
> Takashi Iwai wrote:
>> [my previous post didn't seem to go out by some reason, so I just
>>   resend this; please disregard if you already received it.]
> Hmm, I still can't see this in LKML archives...
> Did you guys receive my previous post below?
>

I did, sorry for not responding, I'm buried under stuff at the moment.

Rafael


>> Hi,
>>
>> we've received a bug report with 3.14.x kernel regarding the firmware
>> loading of intel BT device at suspend/resume:
>>    https://bugzilla.novell.com/show_bug.cgi?id=873790
>>
>> It's a WARN_ON() that was recently introduced.  And, it turned out
>> that the problem basically comes from a small window between the
>> process resume and the clear of usermodehelper lock.
>>
>> The request_firmware() function checks the UMH lock and gives up when
>> it's in DISABLE state.  This is for avoiding the invalid  f/w loading
>> during suspend/resume phase.  The problem is that
>> usermodehelper_enable() is called at the end of thaw_processes().
>> Thus, a thawed process in between can kick off the f/w loader code
>> path (in this case, via btusb_setup_intel()) even before the call of
>> usermodehelper_enable().  Then usermodehelper_read_trylock() returns
>> an error and request_firmware() spews WARN_ON() in the end.
>>
>> The oneliner patch below seems fixing the problem.  But, I'm not quite
>> sure whether it's the best; rather usermodehelper_enable() can be
>> moved there, or better to define yet another state, e.g. UMH_THAWING,
>> instead of reusing UMH_FREEZING?
>>
>> Suggestions?
>>
>> Once when we agree, I'll cook up a proper patch.
>>
>>
>> thanks,
>>
>> Takashi
>>
>> ---
>> diff --git a/kernel/power/process.c b/kernel/power/process.c
>> index 06ec8869dbf1..9c7552f092f2 100644
>> --- a/kernel/power/process.c
>> +++ b/kernel/power/process.c
>> @@ -181,6 +181,8 @@ void thaw_processes(void)
>>   	pm_nosig_freezing = false;
>>   
>>   	oom_killer_enable();
>> +	/* allow request_firmare() at this point */
>> +	__usermodehelper_set_disable_depth(UMH_FREEZING);
>>   
>>   	printk("Restarting tasks ... ");
>>   

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