Am 11.12.2017 um 13:57 schrieb Johannes Berg:
> On Mon, 2017-12-11 at 13:54 +0100, Benjamin Beichler wrote:
>> Am 11.12.2017 um 12:46 schrieb Johannes Berg:
>>>> + spin_lock_bh(&hwsim_delete_lock);
>>>> + while (!list_empty(&delete_radios)) {
>>>> + pr_debug("mac80211_hwsim: wait for deferred radio remove\n");
>>>> + spin_unlock_bh(&hwsim_delete_lock);
>>>> + flush_work(&list_entry(&delete_radios,
>>>> + struct mac80211_hwsim_data, list)
>>>> + ->destroy_work);
>>> This can't possibly be right ... you're locking the list_empty which is
>>> a trivial pointer comparison, but not the actual list_entry() ...
>> Maybe the first spin_lock is not needed, but since flush_work wait for
>> the completion of the task, which at the end also deletes the item from
>> the list, holding any spin_lock would be wrong.
> But not holding it while taking things that are on the list also seems
> wrong.
Since at this place (Netlink is already unregistered so no new deletion
requests) the only user of the delete list is the code deferred work
items (which take itself the lock). Nonetheless, with a separate
workqueue this is no problem anymore.
>
>>> I'd also prefer you actually didn't leave the problem in part as you
>>> describe - and a new workqueue probably isn't that much overhead and
>>> should introduce *less* new code than this, so IMHO that's worth it.
>> I totally agree with you, but I don't know the actual policy for
>> creating workqeues. I could also simply call flush_scheduled_work,
>> because we may have enough time at module unload. Some modules also do
>> it, but the description an some mailing threads mark it like
>> evil/deprecated. Which solution do you prefer?
> Let's go with a new workqueue.
Ok, I prepare a patch in the next few days.
>
> johannes
>
--
M.Sc. Benjamin Beichler
Universität Rostock, Fakultät für Informatik und Elektrotechnik
Institut für Angewandte Mikroelektronik und Datentechnik
University of Rostock, Department of CS and EE
Institute of Applied Microelectronics and CE
Richard-Wagner-Straße 31
18119 Rostock
Deutschland/Germany
phone: +49 (0) 381 498 - 7278
email: Benjamin.Beichler@xxxxxxxxxxxxxx
www: http://www.imd.uni-rostock.de/
