linux-kernel - Re: [RESEND PATCH v1 1/8] firmware_loader: Clear data and size in fw_free_paged

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Message-ID: <16f93247-3af2-e9cb-b7f6-c8305fa1db33@redhat.com>
Date:   Mon, 28 Mar 2022 11:52:25 -0700
From:   Tom Rix <trix@...hat.com>
To:     Russ Weight <russell.h.weight@...el.com>, mcgrof@...nel.org,
        gregkh@...uxfoundation.org, rafael@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     lgoncalv@...hat.com, yilun.xu@...el.com, hao.wu@...el.com,
        matthew.gerlach@...el.com, basheer.ahmed.muddebihal@...el.com,
        tianfei.zhang@...el.com
Subject: Re: [RESEND PATCH v1 1/8] firmware_loader: Clear data and size in
 fw_free_paged_buf


On 3/28/22 11:09 AM, Russ Weight wrote:
> Hi Tom,
>
> On 3/28/22 06:27, Tom Rix wrote:
>> On 3/23/22 4:33 PM, Russ Weight wrote:
>>> The fw_free_paged_buf() function resets the paged buffer information in
>>> the fw_priv data structure. Additionally, clear the data and size members
>>> of fw_priv in order to facilitate the reuse of fw_priv. This is being
>>> done in preparation for enabling userspace to initiate multiple firmware
>>> uploads using this sysfs interface.
>>>
>>> Signed-off-by: Russ Weight <russell.h.weight@...el.com>
>>> ---
>>> v1:
>>>     - No change from RFC patch
>>> ---
>>>    drivers/base/firmware_loader/main.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
>>> index 94d1789a233e..2cc11d93753a 100644
>>> --- a/drivers/base/firmware_loader/main.c
>>> +++ b/drivers/base/firmware_loader/main.c
>>> @@ -253,6 +253,8 @@ void fw_free_paged_buf(struct fw_priv *fw_priv)
>> Why isn't a vfree needed or realloc done?

I am looking at the use of this function in __free_fw_priv

       if (fw_is_paged_buf(fw_priv))
           fw_free_paged_buf(fw_priv);
       else if (!fw_priv->allocated_size)
           vfree(fw_priv->data);

Where it seems like there is another way to set data, so it needs 
another way to unset.

The vfree here looks suspect because the pointer comes in from 
request_firmware_info_buf with a hope that it was allocated by vmalloc.

Tom

> The free and realloc support was present prior to my changes. The page
> buffer support was designed such that if a firmware write was cancelled, the
> existing fw_priv structure could be re-used for another write in the context
> of the same firmware upload. However, there was no prior case for completing
> a write and then reusing the fw_priv structure for subsequent firmware writes;
> fw_priv previously had a one-time use. The changes I have made are to enable
> the re-use of the fw_priv structure.
>
> Initially, fw_priv->data is NULL. The "realloc" functionality happens during
> the write of the data binary attribute here:
>
> https://github.com/torvalds/linux/blob/ae085d7f9365de7da27ab5c0d16b12d51ea7fca9/drivers/base/firmware_loader/fallback.c#L426
>
> The fw_priv->data pointer remains NULL until all data is written and the
> user writes '0' to the loading attribute. The fw_priv->data pointer is set in
> fw_map_paged_buf() which is called here:
>
> https://github.com/torvalds/linux/blob/ae085d7f9365de7da27ab5c0d16b12d51ea7fca9/drivers/base/firmware_loader/fallback.c#L274
>
> In the unmodified code, the fw_priv->data pointer is never cleared. My changes
> reset the pointer to NULL after the memory is released so that the fw_priv can
> be resused.
>
> The new firmware-upload happens in the context of a kernel worker thread and the work
> function is fw_upload_main(). At the end of fw_upload_main(), fw_free_paged_buf()
> is called to do the free. This is the function that is being modified by the lines
> below. This function calls "__free_page(fw_priv->pages[i])" in a loop to free the
> memory pages. It also calls "vunmap(fw_priv->data)" to free the virtual mapping.
> You can see the unmodified implementation of this function here:
>
> https://github.com/torvalds/linux/blob/ae085d7f9365de7da27ab5c0d16b12d51ea7fca9/drivers/base/firmware_loader/main.c#L241
>
> - Russ
>
>> Tom
>>
>>>        fw_priv->pages = NULL;
>>>        fw_priv->page_array_size = 0;
>>>        fw_priv->nr_pages = 0;
>>> +    fw_priv->data = NULL;
>>> +    fw_priv->size = 0;
>>>    }
>>>      int fw_grow_paged_buf(struct fw_priv *fw_priv, int pages_needed)