linux-kernel - Re: [PATCH v3] staging: fbtft: core: set smem_len before fb_deferred_io

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Date:   Thu, 28 Jul 2022 16:39:03 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     "Liu, Chuansheng" <chuansheng.liu@...el.com>
Cc:     Peter Suti <peter.suti@...eamunlimited.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] staging: fbtft: core: set smem_len before
 fb_deferred_io_init call

On Thu, Jul 28, 2022 at 12:49:15PM +0000, Liu, Chuansheng wrote:
> Hi Peter,
> 
> > 
> > The fbtft_framebuffer_alloc() calls fb_deferred_io_init() before
> > initializing info->fix.smem_len.  It is set to zero by the
> > framebuffer_alloc() function.  It will trigger a WARN_ON() at the
> > start of fb_deferred_io_init() and the function will not do anything.
> 
> Please show us the WARN_ON() call stack, then everything is clear.
> It is the driver itself issue to be fixed. I saw Thomas made such
> WARN_ON().

I don't understand the confusion here.  The code is very simple and the
description seems very clear.  No need to redo the patch.  I think
Peter tested it before the WARN_ON() was added so he probably didn't
see the WARN_ON().  I told him to add that because it's pretty obvious
what will happen just from reading the code.

> 
> > 
> > Fixes: 856082f021a2 ("fbdev: defio: fix the pagelist corruption")
> 
> Don't agree with such description.

I don't see how you can disagree?  Before your patch the
fb_deferred_io_init() did not use info->fix.smem_len and now it does.

regards,
dan carpenter