linux-kernel - Re: [PATCH] PM / sleep: Fix request

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Date:	Tue, 15 Jul 2014 14:47:13 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM / sleep: Fix request_firmware() error at resume

On Tuesday, July 15, 2014 08:51:27 AM Takashi Iwai wrote:
> The commit [247bc037: PM / Sleep: Mitigate race between the freezer
> and request_firmware()] introduced the finer state control, but it
> also leads to a new bug; for example, a bug report regarding the
> firmware loading of intel BT device at suspend/resume:
>   https://bugzilla.novell.com/show_bug.cgi?id=873790
> 
> The root cause seems to be 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 UMH_DISABLE state.  This
> is for avoiding the invalid  f/w loading during suspend/resume phase.
> The problem is, however, 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.
> 
> This oneliner patch fixes the issue just by setting to UMH_FREEZING
> state again before restarting tasks, so that the call of
> request_firmware() will be blocked until the end of this function
> instead of returning an error.
> 
> Bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=873790
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@...e.de>

Applied, thanks for fixing this up!

> ---
>  kernel/power/process.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index 0ca8d83e2369..4ee194eb524b 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -186,6 +186,7 @@ void thaw_processes(void)
>  
>  	printk("Restarting tasks ... ");
>  
> +	__usermodehelper_set_disable_depth(UMH_FREEZING);
>  	thaw_workqueues();
>  
>  	read_lock(&tasklist_lock);
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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