linux-kernel - Re: [PATCH] tty: serial: atmel: Check return code of dmaengine

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <039b8f2f-7a8d-56a1-d429-d78317012919@microchip.com>
Date:   Tue, 16 Nov 2021 11:33:44 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <gregkh@...uxfoundation.org>
CC:     <richard.genoud@...il.com>, <jirislaby@...nel.org>,
        <Nicolas.Ferre@...rochip.com>, <alexandre.belloni@...tlin.com>,
        <Ludovic.Desroches@...rochip.com>, <linux-serial@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty: serial: atmel: Check return code of
 dmaengine_submit()

On 11/16/21 10:26 AM, Greg KH wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Tue, Nov 16, 2021 at 06:14:23AM +0000, Tudor.Ambarus@...rochip.com wrote:
>> On 11/15/21 5:58 PM, Greg KH wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> On Mon, Nov 15, 2021 at 04:30:04PM +0200, Tudor Ambarus wrote:
>>>> dma_cookie_t < 0 indicates an error code, check for it.
>>>
>>> Very odd changelog text, please be more descriptive about what is
>>> happening here.
>>>
>>
>> The tx_submit() method of struct dma_async_tx_descriptor is entitled to do
>> sanity checks and return errors if encountered. It's not the case for the
>> DMA controller drivers that this client is using (at_h/xdmac), because they
>> currently don't do sanity checks and always return a positive cookie at
>> tx_submit() method. In case the controller drivers will implement sanity
>> checks and return errors, print a message so that the client will be informed
>> that something went wrong at tx_submit() level.
>>
>>>>
>>>> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
>>>> ---
>>>>  drivers/tty/serial/atmel_serial.c | 10 ++++++++++
>>>>  1 file changed, 10 insertions(+)
>>>>
>>>> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>>>> index 2c99a47a2535..376f7a9c2868 100644
>>>> --- a/drivers/tty/serial/atmel_serial.c
>>>> +++ b/drivers/tty/serial/atmel_serial.c
>>>> @@ -1004,6 +1004,11 @@ static void atmel_tx_dma(struct uart_port *port)
>>>>               desc->callback = atmel_complete_tx_dma;
>>>>               desc->callback_param = atmel_port;
>>>>               atmel_port->cookie_tx = dmaengine_submit(desc);
>>>> +             if (dma_submit_error(atmel_port->cookie_tx)) {
>>>> +                     dev_err(port->dev, "dma_submit_error %d\n",
>>>> +                             atmel_port->cookie_tx);
>>>> +                     return;
>>>
>>> What can a user do with this error message?
>>>
>> will be informed that something went wrong at tx_submit() level.
>>
>>> Have you seen this happen in real life?
>>
>> No. I debugged a locking problem and I observed that dma_submit_error() is not called,
>> so I thought to update this.
>>
>>>
>>> What commit does this "fix"?
>>
>> This is rather an improvement, but if you're looking for a fixes tag, I think
>> we can use:
>> Fixes: 08f738be88bb ("serial: at91: add tx dma support")
>>
>> I'll send a v2 as part of a bigger series. If you find this patch does not worth it,
>> I can as well drop it.
> 
> Please resend it because as-is, I can not take it.
> 

I've sent a v2 of this patch as a part of a larger series:
https://lore.kernel.org/all/20211116112036.96349-1-tudor.ambarus@microchip.com/

The slave DMA usage was wrong in both the DMA controller driver and the
serial driver and patch 1/13 and 3/13 are trying to address that.
v2 of this patch is 2/13. I guess all should be considered for an immutable
branch on the DMA tree.

Cheers,
ta