linux-kernel - Re: usermodehelper lock error at resume

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Date:	Tue, 29 Apr 2014 17:59:56 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
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

At Tue, 29 Apr 2014 17:34:32 +0200,
Rafael J. Wysocki wrote:
> 
> 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.

Don't worry, this isn't any urgent issue.  (And I've been off in the
whole last week in anyway :)

I just wondered why this didn't come up in LKML archive.  But if the
post went out actually, it's fine.


thanks,

Takashi

> 
> 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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