linux-kernel - Re: [PATCH] staging: rtl8192u: Fix sleep in atomic context bug in dm_fsync_timer

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Date:   Mon, 6 Jun 2022 15:11:39 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Greg KH" <gregkh@...uxfoundation.org>
Cc:     linux-staging@...ts.linux.dev, davem@...emloft.net,
        kuba@...nel.org, alexander.deucher@....com, broonie@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: rtl8192u: Fix sleep in atomic context bug in
 dm_fsync_timer_callback

Hello,

On Mon, 6 Jun 2022 07:43:11 +0200 greg k-h wrote:

> On Fri, May 20, 2022 at 02:15:41PM +0800, Duoming Zhou wrote:
> > There are sleep in atomic context bugs when dm_fsync_timer_callback is
> > executing. The root cause is that the memory allocation functions with
> > GFP_KERNEL parameter are called in dm_fsync_timer_callback which is a
> > timer handler. The call paths that could trigger bugs are shown below:
> > 
> >     (interrupt context)
> > dm_fsync_timer_callback
> >   write_nic_byte
> >     kzalloc(sizeof(data), GFP_KERNEL); //may sleep
> >   write_nic_dword
> >     kzalloc(sizeof(data), GFP_KERNEL); //may sleep
> > 
> > This patch changes allocation mode from GFP_KERNEL to GFP_ATOMIC
> > in order to prevent atomic context sleeping. The GFP_ATOMIC flag
> > makes memory allocation operation could be used in atomic context.
> > 
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> 
> What commit id does this fix?

Thanks for your time and reply! 
The commit id this patch fix is 8fc8598e61f6 ("Staging: Added Realtek rtl8192u driver to staging").
 
> And how did you find this issue?  Did you run the code to verify it
> still works properly?

I find this issue by writing codeql query. I am trying to use usb raw-gadget to simulate
rtl8192u card in order to test this code.

What`s more, I found the usb_control_msg() with GFP_NOIO parameter in write_nic_byte() 
and write_nic_dword() may also sleep. So I think use the delayed queue to replace timer
is better. 

Best regards,
Duoming Zhou