linux-kernel - Re: [PATCH] Revert "staging:r8188eu: use lib80211 CCMP decrypt"

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Date:   Mon, 31 Dec 2018 20:17:33 -0600
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Michael Straube <straube.linux@...il.com>,
        gregkh@...uxfoundation.org
Cc:     insafonov@...il.com, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "staging:r8188eu: use lib80211 CCMP decrypt"

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

View attachment "patch_8188eu" of type "text/plain" (765 bytes)