linux-kernel - Re: [PATCH] [RFC] EEE PC hangs when booting off battery

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Message-ID: <49F6DA14.7030608@tuffmail.co.uk>
Date:	Tue, 28 Apr 2009 11:27:32 +0100
From:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
To:	Johannes Berg <johannes@...solutions.net>
CC:	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [PATCH] [RFC] EEE PC hangs when booting off battery

Johannes Berg wrote:
> It seems the only reason lockdep doesn't warn is the detour to userspace
> (modprobe) and the waiting for a userspace task (waiting isn't lockdep
> annotated and I don't think it can be)
>
> It seems you cannot load a module while under _any_ lock, ever, since
> userspace might turn around and do something that requires that lock? I
> think we should probably add a warning to the code that waits for the
> userspace task:
>
> 	debug_check_no_locks_held(current);
>
> Or not? Some purely internal locks _might_ be ok... but how could you
> verify that?
>
>   
>> - ieee80211_wep_init(), which is called with rtnl_lock() held, is
>> blocked in request_module() [waiting for modprobe to load a crypto module].
>>     
>
> Right.
>
>   
>> - modprobe is blocked in a call to flush_workqueue(), caused by closing
>> a TTY.
>>     
>
> Can you point out where? I can't find that.
>   

I posted the calltraces earlier at
<http://marc.info/?l=linux-wireless&m=124074566523506&w=2>.

wait_for_completion
flush_cpu_workqueue
? wq_barrier_func
flush_workqueue
flush_scheduled_work
tty_ldisc_release
? tty_fasyc
tty_release_dev
? free_pgtables
tty_release
__fput
filp_close
sys_close
syscall_call


>> - worker_thread is blocked because the workqueue item linkwatch_event()
>> is blocked on rtnl_lock.
>>     
>
> This I know about.
>
>   
>> I've hacked up a test patch to move wep_init() outside of rtnl_lock, and
>> it solved the problem.  My one caveat is that it would probably be
>> cleaner to move it after rtnl_unlock(), instead of before rtnl_lock(). 
>> I just wasn't 100% sure if that would be safe.  Here's the patch:
>>     
>
> That doesn't seem relevant, this just does some initialisation. However,
> you definitely missed adding a call to wep_free().
>   

Hah, I should have realized something was wrong when I noticed I was
removing more lines that I added. 

The crypto init does cause the module load:

wait_for_completion
call_usermodehelper_exec
__request_module
crypto_larval_lookup
? extract_entropy
crypto_alg_mod_lookup
crypto_alloc_base
ieee80211_wep_init
ieee80211_register_hw
? ath5k_hw_set_bss
ath5k+pci_probe
local_pci_probe
pci_device_probe
driver_probe_device
__driver_attach
bus_for_each_dev
driver_attach
? __driver_attach
buad_add_driver
driver_register
? ktime_get_ts
__pci_register_driver
init_ath5k_pci
_stext
? init_ath5k_pci
? proc_create_data
? register_ieq_proc
kernel_init


Thanks
Alan

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