netdev - Re: [PATCH] net: wireless: iwlegacy: Fix possible data races in il4965_send_rxon

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Date:   Fri, 5 Oct 2018 21:42:55 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Stanislaw Gruszka <sgruszka@...hat.com>
Cc:     kvalo@...eaurora.org, davem@...emloft.net,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: wireless: iwlegacy: Fix possible data races in
 il4965_send_rxon_assoc()



On 2018/10/5 15:54, Stanislaw Gruszka wrote:
> On Thu, Oct 04, 2018 at 04:52:19PM +0800, Jia-Ju Bai wrote:
>> On 2018/10/4 15:59, Stanislaw Gruszka wrote:
>>> On Wed, Oct 03, 2018 at 10:07:45PM +0800, Jia-Ju Bai wrote:
>>>> These possible races are detected by a runtime testing.
>>>> To fix these races, the mutex lock is used in il4965_send_rxon_assoc()
>>>> to protect the data.
>>> Really ? I'm surprised by that, see below.
>> My runtime testing shows that il4965_send_rxon_assoc() and
>> il4965_configure_filter() are concurrently executed.
>> But after seeing your reply, I need to carefully check whether my
>> runtime testing is right, because I think you are right.
>> In fact, I only monitored the iwl4965 driver, but did not monitor
>> the iwlegacy driver, so I will do the testing again with monitoring
>> the lwlegacy driver.
> <snip>
>>> So I wonder how this patch did not cause the deadlock ?
>> Oh, sorry, anyway, my patch will cause double locks...
> So how those runtime test were performend such you didn't
> notice this ?

I write a tool to perform runtime testing.
This tool records the lock status during driver execution.
Some calls to mutex_lock() are in common.c that I did not handle, so the 
corresponding lock status was not recorded by my tool, causing this 
false positive.

Now I have handled common.c, and this false positive is not reported any 
more.
Actually, I get several new reports.
I will send you these reports to you later, and hope you can have a 
look, thanks in advance :)

>
>>> Anyway what can be done is adding:
>>>
>>> lockdep_assert_held(&il->mutex);
>>>
>>> il4965_commit_rxon() to check if we hold the mutex.
>> I agree.
> Care to post a patch ?

Sure :)


Best wishes,
Jia-Ju Bai