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Subject: Re: [PATCH] Revert "staging:r8188eu: use lib80211 CCMP decrypt"
To:     Larry Finger <Larry.Finger@lwfinger.net>,
        Michael Straube <straube.linux@gmail.com>,
        gregkh@linuxfoundation.org
Cc:     devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org
References: <20181230183918.3888-1-straube.linux@gmail.com>
 <efbc3a4a-ce31-8785-73c0-3d89edc66977@lwfinger.net>
From:   Ivan Safonov <insafonov@gmail.com>
Message-ID: <4dd17d38-8c4d-b5db-1091-edba0d95cadf@gmail.com>
Date:   Tue, 1 Jan 2019 12:02:02 +0300
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I suggested a patch for loading modules from interruptible mode, but 
this patch remained unclaimed ( 
http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-August/124851.html 
).

For some reason I thought that this patch had been removed and did not 
track the fate of this code ( 
http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-August/124573.html 
).

On 1/1/19 5:17 AM, Larry Finger wrote:
> On 12/30/18 12:39 PM, Michael Straube wrote:
>> Commit 6bd082af7e36 ("staging:r8188eu: use lib80211 CCMP decrypt")
>> is causing hardfreeze whenever the driver tries to connect to my wifi
>> network. That makes the driver unusable on my system. Reverting the
>> commit fixes the issue and the driver works properly.
>>
>> Dec 29 19:21:17 gentoo kernel: BUG: scheduling while atomic: 
>> swapper/6/0/0x00000100
> 
> Michael,
> 
> I have verified the freezes that you see. Although I have not been able 
> to capture the console dump, I think we are likely seeing the same problem.
> 
> I do have a work-around in that I have not gotten any freezes when I 
> force module lib80211_crypt_ccmp to be loaded before I load module 
> r8188eu. This clue was used in finding what seems to be a good fix.
> 
> I do not know anything about demand loading of modules using 
> try_then_request_module(); however, I noticed that the macro actually 
> calls __request_module(), which has the following comment:
> 
>   * Load a module using the user mode module loader. The function returns
>   * zero on success or a negative errno code or positive exit code from
>   * "modprobe" on failure. Note that a successful module load does not mean
>   * the module did not then unload and exit on an error of its own. Callers
>   * must check that the service they requested is now available not blindly
>   * invoke it.
> 
> I note that it says "user mode module loader". Routine rtw_aes_decrypt() 
> is likely inside some sort of locking, which leads to the "scheduling 
> while atomic" bug that you see. As a result, I suspect that the module 
> is not loaded, and that leads to the NULL dereference when the module is 
> accessed. Please try the one-line patch attached, which forces lib80211 
> to load when r8188eu is loaded. With this patch, I have been connected 
> to an AES-encrypted AP for nearly 3 hours with no problems.
> 
> Larry
> 
>