Re: usermodehelper lock error at resume

[Rafael J. Wysocki]

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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