linux-kernel - Re: [PATCH v3] video: fbdev: vesafb: add missed release

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Date:   Tue, 24 Mar 2020 14:50:15 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Chuhong Yuan <hslester96@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] video: fbdev: vesafb: add missed release_region


On 3/24/20 2:35 PM, Chuhong Yuan wrote:
> On Fri, Mar 20, 2020 at 8:01 PM Bartlomiej Zolnierkiewicz
> <b.zolnierkie@...sung.com> wrote:
>>
>>
>> On 3/10/20 3:35 AM, Chuhong Yuan wrote:
>>> The driver forgets to free the I/O region in remove and probe
>>> failure.
>>> Add the missed calls to fix it.
>>>
>>> Signed-off-by: Chuhong Yuan <hslester96@...il.com>
>>> ---
>>> Changes in v3:
>>>   - Revise the commit message.
>>>   - Add an error handler to suit the "goto error" before request_region().
>>>   - Revise the order of operations in remove.
>>>
>>>  drivers/video/fbdev/vesafb.c | 9 ++++++---
>>>  1 file changed, 6 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c
>>> index a1fe24ea869b..c7bc9ace47d4 100644
>>> --- a/drivers/video/fbdev/vesafb.c
>>> +++ b/drivers/video/fbdev/vesafb.c
>>> @@ -439,7 +439,7 @@ static int vesafb_probe(struct platform_device *dev)
>>>                      "vesafb: abort, cannot ioremap video memory 0x%x @ 0x%lx\n",
>>>                       vesafb_fix.smem_len, vesafb_fix.smem_start);
>>>               err = -EIO;
>>> -             goto err;
>>> +             goto err_release_region;
>>>       }
>>>
>>>       printk(KERN_INFO "vesafb: framebuffer at 0x%lx, mapped to 0x%p, "
>>> @@ -458,15 +458,17 @@ static int vesafb_probe(struct platform_device *dev)
>>>
>>>       if (fb_alloc_cmap(&info->cmap, 256, 0) < 0) {
>>>               err = -ENOMEM;
>>> -             goto err;
>>> +             goto err_release_region;
>>>       }
>>>       if (register_framebuffer(info)<0) {
>>>               err = -EINVAL;
>>>               fb_dealloc_cmap(&info->cmap);
>>> -             goto err;
>>> +             goto err_release_region;
>>>       }
>>>       fb_info(info, "%s frame buffer device\n", info->fix.id);
>>>       return 0;
>>> +err_release_region:
>>> +     release_region(0x3c0, 32);
>>
>> This is incorrect.
>>
>> The cleanup order should be the reverse of the probing order.
>>
>> Also request_region() return value is not checked by the driver
>> (there is a comment that it can fail and is optional):
>>
>>         /* request failure does not faze us, as vgacon probably has this
>>          * region already (FIXME) */
>>         request_region(0x3c0, 32, "vesafb");
>>
>> so what would happen in such case? It seems that unconditionally
>> doing the release will result in freeing the I/O region owned by
>> the other driver (vgacon)..
>>
> 
> Maybe we can add a field to represent whether the request succeeds?
> request_region() returns source *, we can store it and check whether
> it is null when
> we are going to call release_region().

Yes, this is a preferred approach. 

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

>>>  err:
>>>       arch_phys_wc_del(par->wc_cookie);
>>>       if (info->screen_base)
>>> @@ -481,6 +483,7 @@ static int vesafb_remove(struct platform_device *pdev)
>>>       struct fb_info *info = platform_get_drvdata(pdev);
>>>
>>>       unregister_framebuffer(info);
>>> +     release_region(0x3c0, 32);
>>>       framebuffer_release(info);
>>>
>>>       return 0;
>>>
>>
>> Best regards,
>> --
>> Bartlomiej Zolnierkiewicz
>> Samsung R&D Institute Poland
>> Samsung Electronics